Should I replace my gas water heater with indirect?

[jmiller_2308]

Brief question:
What experience do folks have with indirect water heaters running off a boiler? Is it worth replacing my old gas water heater with one in hopes of getting significantly more supply?


Longer explanation:
My Rheem 50 gallon gas water heater is now 23 years old and I'm thinking I should be pro-active and be prepared to replace it. Although it has been good to me, it has also been deficient at supplying enough hot water to fill our 2 person tub even with the temp set to scalding. So I am looking to improve the gallons delivered in the first hour and the question is how best to do that.

I do not have specs on the current heater and only know that it has a 36,000 BTU input. Looking at other Rheem 50 gallon water heaters it seems they have slightly more BTU input and provide from 74 to 86 gallons first hour. Even if the new ones do perform better I doubt they would fill the tub and that would make the wife very unhappy, and hence, me very unhappy.

I have thought about going to a bigger tank but that seems like a huge waste of energy as I'll be keeping a lot of water around for whenever the wife wants to take a bath. It also puts the cost of the heater well above $1000.

I thought about on demand for awhile but I don't like the flow and after an unpleasant run-in with a plumbing sales person I'm really not interested in that deal. Besides, the amount of gas needed to heat the flow I'd need might create an issue with having to resize my gas plumbing.

I happen to have a boiler running my heating system and I recently redid the controls to add a Taco zone control that has a priority zone that could be used to drive an indirect water heater. This sounds attractive to me but I really don't know how well these work or how long they last.

I've seen a few posts on GJ about the amtrol BoilerMate and when I look at the specs for the CH41SZ it seems comparable to the 50 gallon Rheem when the boiler is only 40,000 btu output. However, my Weil McClain boiler is 105,000 BTU input and runs at 180. If I low ball the output of the boiler to 80,000 the CH41SZ claims that the first hour rating is 143 gallons with 139 GPH continuous flow That seems like it should be more than enough to fill the tub and even have slightly less water just hanging around being warm (41 gallons vs. 50).

So what am I missing? Is this really that simple or is there something hidden in the numbers that is causing me to believe this is better than it is?

Also, are there other indirect water heater that folks have had experience with and would recommend?

What say you folks of GJ?

 

[stokefire7]

I have an NTI 50 gal. off my Weil-Mclain 110,000. Family of four. Tank temp. set at 140 with a blender. No issues.
If I remember , the tank was somewhere around $1000.00. Pump I got off E-bay.
I don't think you'll be disappointed.

 

[flat350]

I've done a few when I was still working but they were in monster houses,usually they had a 200 gal. plus tank,one had 2-250 gal. tanks.They seemed to work well,houses usually had very large showers with multiple heads.

 

[yeldogt]

I always do an indirect whenever there is a boiler ... now that SS tanks are around ... that's what I use.

Typically have less standby loss vs a atmospheric tank type water heater and you don't have to pipe in two gas lines and the two flue. But, the tanks cost more -- you do typically have greater input BTU's ... but not always.

Frankly -- for you with the flue and line already there -- it may be easier to get a higher recovery water heater with the output you need.

Big tubs are always an issue. Sometimes people install dedicated gas or even electric on-demand just for the tub. Some big tubs will wipe out any tank .....

Have to do the math ... NG is so cheap.

 

[FANTM58]

I love mine. I am running a boiler and boiler buddy for my radiant heat/snow melt system
So it only makes sense. We’re heating 4000 sq’ of home 1000sq’ of attached garage and a 500 sq` drive way. We’ve never ran out of water. We had to install the water tank in one of the garages, because I ran out of room in the mech room with the boiler buddy and eqpt.

 

[jmiller_2308]

Thanks for the input so far.

I dug around with a flashlight and got a bit more info off my boiler. It is 105,000 BTU in with a D.O.E (Gross output) of 88,000.

I then looked at the NTI and other indirect water heaters and was surprised that many of them call for a much larger gross output from the boiler than I have.

I did find a smaller number of indirects that my boiler specs meet from manufacturers I hadn't heard of before but two notable brands that I'm considering include:

Amtrol (BoilerMate and Hydromax) only require a minimum of 40,000 but first hour rate and continuous go up as boiler output goes up. It seems that with my boiler I should be able to get at least double the first hour rating of my current gas fired boiler.

HTP SuperStor really wants more input than I have but they also have a chart that indicates performance with a smaller boiler. My boiler should drive the ssu-45 to a rate slightly better than the amtrol but at 40% more the cost.

Additional considerations are that I measured the water flow at the faucet of the tub this morning and it is putting out 5 gallons a minute or about 300 gph which is generally twice the continuous flow offered for indirect heaters that can run on my 88,000 output. So to me that says the first hour rate really needs to be able to fill most of the tub. Alternatively, I could fill or top off the tub at 2 gpm to stay at the output of the smaller indirect water heaters.

I have no issues with showers or other hot water consumption other than the tub but to meet the tub requirements it really seems like I'll need at least a 40 gallon capacity when fired at 88,000 btus if I want to make sure the tub is full.

Any suggestions or experience for indirect water heaters that can operate on 88,000 gross output from the boiler?

 

[stokefire7]

You'll have to adjust the numbers. The chart is for max output.
200 F boiler water
50 F incoming potable
In a vague sort of way. I'm speculating your boiler water isn't 200 F and your incoming isn't 50 F either.
My incoming is in the upper 30's. my boiler water 140 F.

 

[stokefire7]

Those are a couple factors that throw off the numbers.

 

[SwampCat]

Been using a Buderus one for 16 years now. new place has a Weil McLain one,14 years old. Stand by losses are nil, recovery is great. Was a no brainer for me. Y.M.M.V.

 

[jmiller_2308]

Thanks again for the input.

My boiler stops at 180 and since I have 300' deep well water I'm pretty sure it is coming in at around 50; at least it doesn't feel colder than that at the tap.

Interpolating from published numbers to my 88,000 gross boiler output is challenging when the numbers for the water heater are asking for more input. I've started contacting the manufacturers to see if they can provide some guidance.

I hadn't seen the Buderus before but I do like the Weil McLain options. Unfortunately, the Weil McLain seem to wany double my available BTUs to run. Hopefully the mfg can give me some guidance.

 

[SwampCat]

Both my boilers, a Buderus and a NTI are 100,000 btu. Both will run 200 degrees if necessary. Have each set at 180 to heat the domestic hot water side.

 

[scottydosnntkno]

If you already have gas ran to the old one, I would seriously consider a good (navien) condensing tankless. As long as your gas meter can support it, a navien npe240 runs 199k btus off a 1/2” gas line, up to 24’ off a 1” main line.

It will do 5.2gpm at a 70 degree rise, which is plenty if your on a well coming in around 50, raised to 120, which at that rate you’re be running maybe 10% cold too to bring it back down to 110 in the tub. They vent and combust through two 2” pvc lines. They’re also variable output, so if you open one sink faucet it runs 80k btu or whatever the demand requires for the output, not 200k.

And, as with all tankless, your not wasting energy keeping stored water warm the 23 hours a day your not using it. But, when you open a faucet, even your 5 gpm tub, it’ll give you hot water all day long with no issues

 

[Jackfre]

what is the volume of the tub? 7.48 gal/ft3. Try to match the load and outputs.

 

[yeldogt]

The tables may show the recovery w/ larger BTU input -- that's because years ago .. all boilers were big and oversized.

It's all about first hour and draw ... remember a typical 40g water heater has 26k btu burner.

What does the tub need -- that's what you have to have available.

Yes the standby is lower -- but NG is cheap. 40g at higher temps is what I do ....

 

[jmiller_2308]

I looked into on demand awhile ago and although I know things have changed they are still not an option I'm interested in.

Thanks for the prompting on the sizing of the tub. Unfortunately I have no literature for it and am reticent to try to measure it to full. However, I know the flow rate of of the faucet so I'll just have the wife stop watch the next time she fills it so that I can get a ball park size.

 

[Justind97]

Honestly, I think once you go to tankless you'll wonder why you didn't go that route before. I know you have a sour taste from one bad salesman, but it's likely the best thing that we have going in our house.

I can take a 40 minute shower and never have to worry about losing hot water or using it all up.
They also take up a heck of a lot less space than a hot water tank.

Tankless pretty much solves all the problems you are trying to address.

 

[rlitman]

Honestly, I think once you go to tankless you'll wonder why you didn't go that route before. I know you have a sour taste from one bad salesman, but it's likely the best thing that we have going in our house.

I can take a 40 minute shower and never have to worry about losing hot water or using it all up.
They also take up a heck of a lot less space than a hot water tank.

Tankless pretty much solves all the problems you are trying to address.

You can take a 40 minute shower, but if you have two showers in the house, you can't use them simultaneously, or else both will get cold water.

I have three showers in my house, and regularly have two on at the same time. Two have rain shower heads, and the third has had the flow restricter removed. My 50 gallon indirect will supply them all at once, but 50 gallons of water disappears pretty quickly with high flow heads, even if it recovers in under 20 minutes. It's particularly an issue towards the end of winter, when the main from the street is coming in below 40F while people take hotter showers.

So, I went the insane route and came up with something different. I tapped into the boiler loop that supplies the heating jacket for the indirect with monoflo tees, and run that water through a flatplate heat exchanger. The cold water that fills the DHW indirect tank goes through the other side of the heat exchanger before entering the tank. If the tank is already hot, it does nothing. But when the tank is calling for heat, it pre-heats the water that fills the tank to around 90F. At that point, the water jacket heating the tank takes over, and by the time that water circulates to the top, its plenty hot to supply a shower.

Also, I have the hot water from my tank going through a mixing valve before being sent via the manifold to the showers and lavatory sinks (the dishwashers and washing machines get it straight from the tank). So, the temperature of the water reaching the shower valve hardly changes with any amount of use.

 

[Justind97]

You can take a 40 minute shower, but if you have two showers in the house, you can't use them simultaneously, or else both will get cold water.

Sure you can. We do it all the time.

That's not how a tankless system works. When the system gets taxed too much, it slows the rate of hot water coming out in an attempt to keep up the temp set on the unit, ie 120 degrees..

The solution is just to turn up the temperature in the shower a bit past what it's normally at.

It's not as if by using two different sources pulling hot water that the system stops working..

 

[kj_mustang]

I have a 95,000 btu condensing boiler with a 40 gal. external DHW tank. The DHW loop has priority over the radiant loops. I have the external tank temperature set to about 134. The sensor is about 2/3 down in my tank so it is hotter up top. It does have a mixing valve at the HW supply. My boiler water temp will get up to 180's when the HW loop is running. I never run out of hot water but it is only a family of 3 so not taxing it. Here is the specs for the ext. tank for you.

Boiler Output Btu/Hr : 112,000
1st Hour Recovery (gal) : 180
Continuous Flow (gal) : 150
Peak/Flow (gal/10 min.) : 50

 

[rlitman]

...That's not how a tankless system works. When the system gets taxed too much, it slows the rate of hot water coming out in an attempt to keep up the temp set on the unit, ie 120 degrees...

None that I've ever seen do that. Every one I've ever seen would allow all the flow, and the supplied temperature drops with increasing flow.

 

[Jackfre]

My 80% tankless unit with a 180 kbtu input and 55* incoming temp would deliver 4.3 gpm of 120* water. In my shower with a 2.5 gpm shower head it took 2.1 gpm of hot with the .4 of cold to be at my desired shower temp. The 199 kbtu 95% units are delivering in the 6gpm range. In southern climates with warmer water inlets those numbers rise. In the northern areas where, as noted, the inlet temps get depressed as the frost drives to the mains I saw, with my 180 unit a reducing of output of .4gpm/10* reduction of supply temp.
For filling a tub, given that if you sit in a tub over 105* you are no longer bathing but are par-boiling the output gpm is increased. When at my daughters house I pull up the app and tell the water heater I want 35 gal of 102* water for the grandkids tub and that is what it delivers. When done it shuts down. I'm generally not one for fancy stuff, but I like this feature.
It all depends upon what your connected load is. I had a guy with a 25 gpm shower load. It spec'd out at a bank of 5 tankless units tied together. He had a modulating water system that would go from 15,000 btu up to 900,000 btu depending upon flow requirements.
To our OP, I am not looking for the capacity of the tub to .1 gal. Do a WxLx approx depth you fill the tub and report back. Also, get a 5 gal pail and do a timed flow out of your tub fill.

 

[jmiller_2308]

I have a 95,000 btu condensing boiler with a 40 gal. external DHW tank. The DHW loop has priority over the radiant loops. I have the external tank temperature set to about 134. The sensor is about 2/3 down in my tank so it is hotter up top. It does have a mixing valve at the HW supply. My boiler water temp will get up to 180's when the HW loop is running. I never run out of hot water but it is only a family of 3 so not taxing it. Here is the specs for the ext. tank for you.

Boiler Output Btu/Hr : 112,000
1st Hour Recovery (gal) : 180
Continuous Flow (gal) : 150
Peak/Flow (gal/10 min.) : 50

Thanks for that info as it sounds pretty close to what my setup would be if I ran with my current boiler and a tank rated for a higher input. However, I also seem to be narrowing in on the Amtrol Hydromax HM-41L which my boiler can easily supply and for which I think the Ener-G-Net controller might really help with smoothing out boiler runs in low demand times.

I have no issues with showers, dishwasher, laundry, etc. all running at the same time with my current 50 gallon gas water heater but I do have issue filling the tub. I still need to get a volume size for the tub but after all the discussions I'm pretty sure an indirect water heater will provide a much greater first hour rate than my current water heater and should also easily address the tub.

As for the discussions about tankless I remain unconvinced. To get the gpm I'd be happy with it would likely cost as much for the tankless as it would for an indirect but considering the additional gas supply upgrade and that I would likely hire somebody to install it the installation costs would be a great deal more. I feel comfortable with my skills to install the indirect and I wouldn't have to worry about new intake/exhaust venting to handle that much more air exchange. All in all, my seat of the pants estimate is that a tankless would likely cost me at least twice what an indirect would cost me.

I didn't search long but just looking at some of the reviews of the bigger tankless also seems to indicate quite a few unhappy customers with leaking and worn out parts in short periods of time. I suspect that an indirect will likely last longer and require a lot less maintenance than a tankless.

And one last concern about tankless is the lag from when the heater fires until hot water is at the tap. I have a rambler with long runs to the master bath and adding additional delay is just not something I'm interested in. I had a circulation line installed when the house was built and recently added a circulation pump to that line to make sure water is at the tap immediately when I turn it on. The circulation pump only runs just prior to my wake up and sleep times so it isn't on all the time but I still wonder how using a circulation line and pump would impact a tankless.

 

[kj_mustang]

I have a recirculation loop on my 2 story house with a digital timer hooked up to power the pump. I have about 4-5 10 minute long cycles programmed. Works really well with the external tank.

 

[u3b3rg33k]

And one last concern about tankless is the lag from when the heater fires until hot water is at the tap. I have a rambler with long runs to the master bath and adding additional delay is just not something I'm interested in. I had a circulation line installed when the house was built and recently added a circulation pump to that line to make sure water is at the tap immediately when I turn it on. The circulation pump only runs just prior to my wake up and sleep times so it isn't on all the time but I still wonder how using a circulation line and pump would impact a tankless.

A lot of the Rinnai's have the ability to play nice with a recirculation setup - they list it in the features. I assume the "ideal" way to do that is have an occupancy sensor (motion, button, etc) tell it to fire just before the demand starts but they probably work with continuous systems as well.

 

[scottydosnntkno]

You can take a 40 minute shower, but if you have two showers in the house, you can't use them simultaneously, or else both will get cold water.

I have three showers in my house, and regularly have two on at the same time. Two have rain shower heads, and the third has had the flow restricter removed. My 50 gallon indirect will supply them all at once, but 50 gallons of water disappears pretty quickly with high flow heads, even if it recovers in under 20 minutes. It's particularly an issue towards the end of winter, when the main from the street is coming in below 40F while people take hotter showers.

So, I went the insane route and came up with something different. I tapped into the boiler loop that supplies the heating jacket for the indirect with monoflo tees, and run that water through a flatplate heat exchanger. The cold water that fills the DHW indirect tank goes through the other side of the heat exchanger before entering the tank. If the tank is already hot, it does nothing. But when the tank is calling for heat, it pre-heats the water that fills the tank to around 90F. At that point, the water jacket heating the tank takes over, and by the time that water circulates to the top, its plenty hot to supply a shower.

Also, I have the hot water from my tank going through a mixing valve before being sent via the manifold to the showers and lavatory sinks (the dishwashers and washing machines get it straight from the tank). So, the temperature of the water reaching the shower valve hardly changes with any amount of use.

Tankless can still easily resolve this problem. But, it will take more than one.

So you have to decide what’s better, unlimited hot water or money.

My house has two navien npe240s, so based on our well water incoming temp of 53 degrees we get 11.2gpm of 123 degree water. Or the equivalent of FIVE normal showers running 2.5gpm, or the highest flow fixture typically seen in residential. They were about $1300 each. But we have literally unlimited hot water for our household, as it only has four showers. Sinks, washers, dishwashers etc are minimal hot water usage. Its showers and tubs that are your long term, high usage items

 

[scottydosnntkno]

Thanks for that info as it sounds pretty close to what my setup would be if I ran with my current boiler and a tank rated for a higher input. However, I also seem to be narrowing in on the Amtrol Hydromax HM-41L which my boiler can easily supply and for which I think the Ener-G-Net controller might really help with smoothing out boiler runs in low demand times.

I have no issues with showers, dishwasher, laundry, etc. all running at the same time with my current 50 gallon gas water heater but I do have issue filling the tub. I still need to get a volume size for the tub but after all the discussions I'm pretty sure an indirect water heater will provide a much greater first hour rate than my current water heater and should also easily address the tub.

As for the discussions about tankless I remain unconvinced. To get the gpm I'd be happy with it would likely cost as much for the tankless as it would for an indirect but considering the additional gas supply upgrade and that I would likely hire somebody to install it the installation costs would be a great deal more. I feel comfortable with my skills to install the indirect and I wouldn't have to worry about new intake/exhaust venting to handle that much more air exchange. All in all, my seat of the pants estimate is that a tankless would likely cost me at least twice what an indirect would cost me.

I didn't search long but just looking at some of the reviews of the bigger tankless also seems to indicate quite a few unhappy customers with leaking and worn out parts in short periods of time. I suspect that an indirect will likely last longer and require a lot less maintenance than a tankless.

And one last concern about tankless is the lag from when the heater fires until hot water is at the tap. I have a rambler with long runs to the master bath and adding additional delay is just not something I'm interested in. I had a circulation line installed when the house was built and recently added a circulation pump to that line to make sure water is at the tap immediately when I turn it on. The circulation pump only runs just prior to my wake up and sleep times so it isn't on all the time but I still wonder how using a circulation line and pump would impact a tankless.

Modern HE condensing tankless are nothing special from an installation standpoint.

Get yourself a navien npe240. It’ll cost you $1350. Plumb the hot and cold supply to it. Run your 1/2” gas line (as long as it’s less than 24’ from a main at least 1” dia). Plug it in and enjoy 4-7gpm hot water for as long as your tap is open.

Check the seat of your pants.

Other than the unit, which comes with the pvc terminations you’d need 20-80’ of 2” pvc and fittings (40-120$) and that’s it. There’s nothing fancy or special about it.

Naviens have a built in recirculation pump and holding tank. They have a couple options. You can run it to always be on, so anytime the water in the loop dips below 100 it will fire partially to reheat it. Or you can set it to only run on a set schedule from say 8-10a and 5-8p, which sounds like what you have now. Or you can set it to smart mode where it will continually update its algorithm to meet your typical needs. If your current one is set to 8-10a, but 95% of the time you shower from 845-930, it will run from 840-935 saving you money.

Tankless are ‘new’ technology that’s been around 20 years. With a modem, high efficiency condensing gas tankless there is virtually zero reasons not to use one over a tanked unit. It’s not like an electric unit that will require a main service upgrade anymore

 

[yeldogt]

Tankless have been around for a long time -- way more than 20 years.

People are mixing things up on this thread ... never running out of hot water taking showers in not the same as filling up a large tub. A standard tub is no problem for a 40g tank at 130.

It's not going to work if you need 50 gal to fill the tub. You need 50 gal ....

Tankless can be a pain if you have long runs -- even the new ones fluctuate. I was just in a new house with one and thermostatic valves. It still had some playing around factor.

Not all indirects are the same -- design matters for heat transfer. My old Buderus steel thermoglase had mass .. and big internal pipes for heat transfer. Same 40g capacity -- but the mass of the unit held heat. That heat tempered the incoming cold -- the new SS have little mass. Same with the plastic.

The OP needs to figure out the peak flow over the fill time. If he does not want to do that .. no one can help him.

Having a recirculation loop -- goes against the point of the on-demand ... but, it can solve some issues. They don't really save all that much $$ vs a typical tank ..... but if you get everybody to switch -- the gas usage adds up.

They are really ideal for single point use .... Like my outside shower at the beach. It has a set temp -- turn the knob

 

[scottydosnntkno]

Tankless have been around for a long time -- way more then 20 years.

People are mixing things up on this thread ... never running out of hot water taking showers in not the same as filling up a large tub. A standard tub is no problem for a 40g tank at 130.

It's not going to work if you need 50 gal to fill the tub. You need 50 gal ....

Tankless can be a pain if you have long runs -- even the new ones fluctuate. I was just in a new house with one and thermostatic valves. It still had some playing around factor.

Not all indirects are the same -- design matters for heat transfer. My old Buderus steel thermoglase had mass .. and big internal pipes for heat transfer. Same 40g capacity -- but the mass of the unit held heat. That heat tempered the incoming cold -- the new SS have little mass. Same with the plastic.

The OP needs to figure out the peak flow over the fill time. If he does not want to do that .. no one can help him.

Having a recirculation loop -- goes against the point of the on-demand ... but, it can solve some issues. They don't really save all that much $$ vs a typical tank ..... but if you get everybody to switch -- the gas usage adds up.

They are really ideal for single point use .... Like my outside shower at the beach. It has a set temp -- turn the knob

OP has already stated that he measured 5gpm flow at the tub. And it’s apparently a large tub so he needs more than one 40 gal tank worth.

So he would rather install a fancy indirect tank hoping to get enough first hour recovery, which isn’t even that useful for his situation as 5gpm will empty a 50g tank in ten mins, and the heater can’t recover that fast to reheat the entire tank to empty again ten mins later. He really needs to look at filling the tub in 20 mins probably, not 60 so it’s not really ‘first hour’ delivery.

Or, he can just install one tankless, that can give 5 gpm flow and fill the tub with no problems and never run out of hot water.

It’s kind of like the direct, easy route vs the over complicated and engineered method.

You can but these ten things and rig it together and spend hours and days getting it to work right and still probably not have enough water. Or you buy this item that will deliver exactly what your looking for, plug it in and know you’ll have plenty of hot water.

 

[Jackfre]

Having "on-demand recirc" with an on-demand tankless water heater is the ideal situation, IF things are right with the piping. At my daughters home I installed the new RUR unit by Rinnai. It has the circulator on board. I also added the wireless control, a wireless push button (kitchen) and a wireless motion sensor (M BA). Whoever plumbed this house should get his *** kicked. It is virtually impossible to have a longer run of hot water piping to supply the kitchen and M BA directly above. The water heater is in the most remote corner of the house from the main loads. I did the crawl in the 16" crawl space to run a direct 3/4" pex recirc line. Previously it took 2.5+ minutes to get hot water to the kitchen sink with either the tankless or the old tank. Now it is about 10 seconds. Here in CA the energy side of things pales in comparison to the water conservation needs.
The comments on 1/2" gas lines while true are not totally accurate. I'm not trying to pick a fight. Yes, you can run up to 20' of 1/2" to the Navien's and the Rinnai's and possibly others, but again it is a connected load issue. Both these units have negative pressure gas valves and will not "fault" when under supplied with gas. They will however produce less hot water than when they are supplied with the proper gas pressure. I have seen many piped with 1/2" and they don't live up to the billing. A call to tech service and the message is, "You gas line is undersized."
These things cost enough that you want to make sure you understand the entire system issues before moving forward with them. They are not hard to do, but it seems so often they are hard to do well. Look before you leap!

 

[kmacht]

A standard bath tub is around 80 gallons. Unless you have a huge jetted tub I don't see why a standard 50 gallon water heater can't fill it. Are you basing everything off the fact that your 23 year old water heater isn't keeping up? Are you sure it is really 50 gallons and you don't have years of sand and sludge in the bottom of that tank? Also, rarely would you fill a bath tub with just pure hot water as it will be too scalding hot to use. Most people mix it with both hot and cold as they are filling.

 

[yeldogt]

OP has already stated that he measured 5gpm flow at the tub. And it’s apparently a large tub so he needs more than one 40 gal tank worth.

So he would rather install a fancy indirect tank hoping to get enough first hour recovery, which isn’t even that useful for his situation as 5gpm will empty a 50g tank in ten mins, and the heater can’t recover that fast to reheat the entire tank to empty again ten mins later. He really needs to look at filling the tub in 20 mins probably, not 60 so it’s not really ‘first hour’ delivery.

Or, he can just install one tankless, that can give 5 gpm flow and fill the tub with no problems and never run out of hot water.

It’s kind of like the direct, easy route vs the over complicated and engineered method.

You can but these ten things and rig it together and spend hours and days getting it to work right and still probably not have enough water. Or you buy this item that will deliver exactly what your looking for, plug it in and know you’ll have plenty of hot water.

First hour delivery is typically the best you can get from the water heater manufacturers -- it's really used for multi shower use. Years ago the tub manufacturers would publish a tank rating/ size they recommended -- the faucet delivery amount has no relevance .. it's all about the amount needed.

I'm not a fan of the on demand. I'm building a new house and can do anything I want -- with something all new and a boiler ... the indirects make sense.

When my parents built years ago .. back when those big tubs were popular -- the solution was a dedicated water heater. Today -- If I was doing one .. a small dedicated on-demand would be the way to go. My sister did an electric .. cheap to install and small -- how much does it cost to heat the tub for the little most are used?

 

[yeldogt]

Having "on-demand recirc" with an on-demand tankless water heater is the ideal situation, IF things are right with the piping. At my daughters home I installed the new RUR unit by Rinnai. It has the circulator on board. I also added the wireless control, a wireless push button (kitchen) and a wireless motion sensor (M BA). Whoever plumbed this house should get his *** kicked. It is virtually impossible to have a longer run of hot water piping to supply the kitchen and M BA directly above. The water heater is in the most remote corner of the house from the main loads. I did the crawl in the 16" crawl space to run a direct 3/4" pex recirc line. Previously it took 2.5+ minutes to get hot water to the kitchen sink with either the tankless or the old tank. Now it is about 10 seconds. Here in CA the energy side of things pales in comparison to the water conservation needs.
The comments on 1/2" gas lines while true are not totally accurate. I'm not trying to pick a fight. Yes, you can run up to 20' of 1/2" to the Navien's and the Rinnai's and possibly others, but again it is a connected load issue. Both these units have negative pressure gas valves and will not "fault" when under supplied with gas. They will however produce less hot water than when they are supplied with the proper gas pressure. I have seen many piped with 1/2" and they don't live up to the billing. A call to tech service and the message is, "You gas line is undersized."
These things cost enough that you want to make sure you understand the entire system issues before moving forward with them. They are not hard to do, but it seems so often they are hard to do well. Look before you leap!

I'm using expensive equipment in my new build -- so the particular indirect tank is expensive. But ... in general you can get them in the $1100 range. My Buderus SS 40 was around $1400 a couple years ago. It's hard to say how much adding an indirect costs when doing a new install w/ boiler ... I have never had one priced out of a job to see the cost. Years ago they must have been more as you would often see both a boiler and tank unit next to one another ... common flue.

Anyway -- the SS Buderus replaced one that was almost 25 years old. So the equipment cost was less than even using a cheep NG gas tank unit for me.

The indirects are rebate driven -- for the average user on NG ... the saving can't be much as my whole gas bill in the shoulder seasons is so low ---- and I cook and have a gas dryer. As I said above .. add up all the houses in the country and I can see the effect.

My indirects don't need to refresh overnight -- the refresh in the Am if needed. So for our uses there may be one very short boiler burn to the tank a day. After that it's just reheating.

As I said above -- for my outdoor shower at the beach .. it's perfect. It may well be the solution for the OP.

 

[jmiller_2308]

Been busy so I'm a bit slow getting back.

5gpm is what my faucet flows at the tub. the tub is 120 gallons.

The guidance I've been reading says a conventional water heater should be about 2/3 the size of the tub in order to fill it. 2/3 of 120 would mean I'd need a 80 gallon tank and since I currently only have a 50 gallon it makes sense that I can't quite fill the tub.

Filling the tub is my only issue. I do not have any issues or need for infinite hot water supply. First hour rate is really my driving ambition and that first hour needs to be able to fill 120 tub to something around 100 degrees. If I can do that with a tank (conventional or indirect) at a reasonable cost than that is what I'd like to do.

I liked the discussion about the navien having its own recirculation built in and so I looked at them again a little more closely. Unfortunately I see some complaints that are often written off as improper installations; that sounds like a warning to me trying to install it myself. I also have concerns about installation issues (gas pipe, intake, and exhaust see below).

Cost is an issue. The navien and other tankless can cost roughly the same as an indirect but I can plumb the indirect. I see a comment above about how you could use 1/2 gas line to feed the navien but that it wouldn't necessarily operate at full efficiency. That makes sense to me because unless you up the pressure you aren't going to get 199000 btus through that line. The run from my manifold to where I'd install the heater is also dang close to 20'. Needless to say, it seems like my seat of the pants of having to run more gas would indeed up the cost of the tankless.

Additionally, measuring and ensuring the proper gas supply makes it to the tankless is something that requires tools and knowledge I do not possess. This brings me back to needing to hire somebody which again means more costs.

With an indirect, I already know how to plumb, wire, and configure the boiler and all the parts are already in place. In my case, there is probably less plumbing for an indirect than if I were to do a tankless and because I can do the indirect vs. hiring to have somebody install the tankless I believe my seat of the pants estimate is correct. That is, for me, the tankless would cost significantly more.

And then there are the aesthetics that I mentioned before. The navien and other heaters of that ilk require plastic tubes out the wall and because of the location of the utility room in the house that would mean sticking ugly plastic pipes out the front of the house next to the main entrance. No thank you.

I like what I'm hearing about first hour rate and longevity of indirect water heaters and ultimately I think that is the best route to fill my tub without going with a more expensive to purchase and operate bigger gas water heater, or a more expensive installation of a tankless option.

 

[redmondjp]

None that I've ever seen do that. Every one I've ever seen would allow all the flow, and the supplied temperature drops with increasing flow.

Same with my Bosch Aquastar. It will run one item, period. If you so much as turn on a sink to wash your hands, the person in the shower gets the cold water sandwich.

And I went from a natural gas tank, located inside heated space in the laundry room, to this tankless unit. It didn't save me any money at all, since any heat lost to the house is less heat that the furnace has to put in, for 9 months of the year. It is nice to be able to take infinitely-long showers however.

I'm actually going to go back to a tank - natural-gas-fired, high-efficiency, with a stainless-steel tank, so I will have 80 gallons of water on hand in case of a natural disaster (the big earthquake, where I am at).

 

[u3b3rg33k]

Been busy so I'm a bit slow getting back.

5gpm is what my faucet flows at the tub. the tub is 120 gallons.

The guidance I've been reading says a conventional water heater should be about 2/3 the size of the tub in order to fill it. 2/3 of 120 would mean I'd need a 80 gallon tank and since I currently only have a 50 gallon it makes sense that I can't quite fill the tub.

Filling the tub is my only issue. I do not have any issues or need for infinite hot water supply. First hour rate is really my driving ambition and that first hour needs to be able to fill 120 tub to something around 100 degrees. If I can do that with a tank (conventional or indirect) at a reasonable cost than that is what I'd like to do.

I liked the discussion about the navien having its own recirculation built in and so I looked at them again a little more closely. Unfortunately I see some complaints that are often written off as improper installations; that sounds like a warning to me trying to install it myself. I also have concerns about installation issues (gas pipe, intake, and exhaust see below).

Cost is an issue. The navien and other tankless can cost roughly the same as an indirect but I can plumb the indirect. I see a comment above about how you could use 1/2 gas line to feed the navien but that it wouldn't necessarily operate at full efficiency. That makes sense to me because unless you up the pressure you aren't going to get 199000 btus through that line. The run from my manifold to where I'd install the heater is also dang close to 20'. Needless to say, it seems like my seat of the pants of having to run more gas would indeed up the cost of the tankless.

Additionally, measuring and ensuring the proper gas supply makes it to the tankless is something that requires tools and knowledge I do not possess. This brings me back to needing to hire somebody which again means more costs.

With an indirect, I already know how to plumb, wire, and configure the boiler and all the parts are already in place. In my case, there is probably less plumbing for an indirect than if I were to do a tankless and because I can do the indirect vs. hiring to have somebody install the tankless I believe my seat of the pants estimate is correct. That is, for me, the tankless would cost significantly more.

And then there are the aesthetics that I mentioned before. The navien and other heaters of that ilk require plastic tubes out the wall and because of the location of the utility room in the house that would mean sticking ugly plastic pipes out the front of the house next to the main entrance. No thank you.

I like what I'm hearing about first hour rate and longevity of indirect water heaters and ultimately I think that is the best route to fill my tub without going with a more expensive to purchase and operate bigger gas water heater, or a more expensive installation of a tankless option.

it's not hard at all. did one at my friends house, we tapped off the 1" main with unions and ran 1" right up to the heater - even the drip leg is 1". 3/4" adapter right at the heater inlet. black pipe is cheap, as is the pipe die.

 

[jmiller_2308]

it's not hard at all. did one at my friends house, we tapped off the 1" main with unions and ran 1" right up to the heater - even the drip leg is 1". 3/4" adapter right at the heater inlet. black pipe is cheap, as is the pipe die.

I too have run gas pipe in both copper and black and have no actual concerns about doing this plumbing.

What I do have concern about is being able to measure the pressure at the heater and ensuring it gets what is needed. There is a HUGE difference between plumbing a 36,000 btu gas heater and a 199,000 btu tankless heater. Everything from pipe size, regulators, restrictions, etc. are a much bigger deal when flowing that much gas.

I'd rather not spend large $'s on something I can't make work to its full extent, or that would starve my other appliances, or that could potentially go boom. That is why I'd feel the need to hire somebody that can measure and balance the system as needed.

 

[sberry]

No replacement for displacement. Could simply plumb another common electric heater in series ahead of it, turn it on or up when you want it.

 

[scottydosnntkno]

it's not hard at all. did one at my friends house, we tapped off the 1" main with unions and ran 1" right up to the heater - even the drip leg is 1". 3/4" adapter right at the heater inlet. black pipe is cheap, as is the pipe die.

Even easier is just using csst. A 50’ roll of 3/4 is like $75. Two $13 fittings in each end and your good to go in about a half hour of time. If you can hook up a sink supply line, you can run csst it’s super easy

 

[kj_mustang]

Even easier is just using csst. A 50’ roll of 3/4 is like $75. Two $13 fittings in each end and your good to go in about a half hour of time. If you can hook up a sink supply line, you can run csst it’s super easy

You forgot the bonding clamps and ground wire.

 

[scottydosnntkno]

You forgot the bonding clamps and ground wire.

If it’s connecting to existing rigid gas pipe, then It doesn’t need it’s own bonding/grounding. The metal fittings bond onto the black pipe, which should be grounded.