Boiler vs. Tankless vs. Tank type water heater

jlckmj · Oct 22, 2012

hi everyone,

Instead of muddying up the waters one of the other threads I decided to start another to debate the merits of the three choices for radiant heating in a garage or shop. I would like to limit it to a garage or shop because a house or a house floor and domestic hot water combined system would bring many factors into the mix that most garages will not have nor need.

We have the proponents that seem to foster the idea that if you are not using a boiler with all the latest triple & quadruple resets, and all the other bells and whistles, (and price tag to go along with it) you have a system that will not work properly, or will not work very long.

After listening to people with that train of thought, I almost gave up on installing a radiant heating system in my new garage. I have to say that I am happy that I did not listen to (him) them. Instead, I started to do some research for myself.

I started by sending PM's to many members on the GJ board to learn the pluses and minuses of their systems and what their systems were using.

I also talked with my plumber, and he stated that he has personally installed 6-7 radiant systems in garages using conventional tank type water heaters, and a couple with tankless type heaters. Several of them are going on 10 years old, and they are all still functioning today, with only one of them having to replace a water heater.

I then talked with my heating contractor who I trust, I asked him what I should use, and he also advised me to use a tank type. One of the first things out of his mouth was that you can replace a lot of water heaters for the amount of money you will spend on a boiler.

By the way, both contractors do a lot of work for my son who is a general contractor, so I felt very confident that they were not going to B.S. me. Also, both knew that I was going to be installing the system myself so they did not have any monetary reasons to lead me in any particular direction.

At one point in my research, I ran across the following website

http://www.jlconline.com/Images/Using Water Heaters for Radiant Heat_tcm96-1156462.pdf

This person states that there are MANY reasons he prefers to use water heaters INSTEAD of boilers. He is advocating using a very expensive water heater, but I think that is at least partially because he does not want the call backs after installing a system, and I don't blame him. To me it sounds like his reasoning is sound, like it or not.

I personally installed a cheap tank type water heater, mainly for budget reasons, and I have every indication that it will work just fine, and I don't feel as though I will be sorry I did what I did. I did consider using a tankless heater, in fact if my water heater takes a puke, I probably will, if for no other reason other than space savings. (the only thing I don't like about my system is the fact it take up a lot of wall space)

However I will NEVER be installing a multi thousand dollar boiler at any time, I will hang a Modine instead.

I hope this helps some of the people that are on the fence about installing radiant heat. Do not let the NAYSAYERS talk you out of it, do your own research, you will be glad you did. Just remember, there are a lot of low cost, no frills systems out there that are operating just fine.

Please feel free to insert your particular favorite type of system, but after you tell us what you feel we should all be buying and why, please include the estimated price tag so we can judge accordingly.

For those that have operating systems "ON THE CHEAP" (like me) feel free to explain it, also please please include a general idea of the cost of your system.

Jim

philjafo · Oct 22, 2012

Well said, gas fired tank water heaters do work and many out there have been working for a long time. The reason to upgrade to tankless are like noted in your post size and there's also efficiency because they typically burn air from outside. The reason to go with a boiler would be if it also handles home heating, multiple zones, different temp zones. It all comes down to using the right tool for the job, and usually the more a tool is needed to do the more it cost.

Fastback · Oct 22, 2012

I like cheap systems myself, but they have to work. What's the point of buying a car that gets 70mpg if it costs $70000.00, you can buy a lot of fuel for a cheap civic with the difference, you may not look as cool but you will get there.

My systems cost are spelled out for everyone to see, it heats 720 square feet to 65 degrees for an annual cost of under $400.

Would I try to heat a 4000sf shop with it, no that would be silly.....I would use four of them in independant zones lol.

You really don't need additional mixing pumps with this radiant design since you have adjustability in both flow rate and temperature. And once the floor is at a decent temp it really loafs along. This type of heater, when used as a traditional water heater, can take ground water in the wintertime and scald you with it, so turning 55 or 60 degree water up to 120 is no big load and if you get a close delta in your system it's capable of modulating itself down to a cost effective solution.

wedge40 · Oct 23, 2012

Just my two cents worth. If the shop is sealed and fairly well insulated then the heater and pump shouldn't have to work to hard. When I finally get around to putting heat to my system, I'll probably be using a tankless heater. I do have a little larger area to heat then most, 2240 sqf, but should be sealed and insulated so once up to temp shouldn't take much to heat. Like the OP said, I can get a bunch of heaters for the cost of one boiler.

Wedge

kert · Oct 23, 2012

Fastback said:
I like cheap systems myself, but they have to work. What's the point of buying a car that gets 70mpg if it costs $70000.00, you can buy a lot of fuel for a cheap civic with the difference, you may not look as cool but you will get there.

My systems cost are spelled out for everyone to see, it heats 720 square feet to 65 degrees for an annual cost of under $400.

Would I try to heat a 4000sf shop with it, no that would be silly.....I would use four of them in independant zones lol.

You really don't need additional mixing pumps with this radiant design since you have adjustability in both flow rate and temperature. And once the floor is at a decent temp it really loafs along. This type of heater, when used as a traditional water heater, can take ground water in the wintertime and scald you with it, so turning 55 or 60 degree water up to 120 is no big load and if you get a close delta in your system it's capable of modulating itself down to a cost effective solution.

I'm interested in your Titan water heater. How much adjustability is there in the set-point?

Fastback · Oct 23, 2012

It is the older version with a simple knob adjust so it does not show a range, but on high it sends 170-180 out. I run it between low and medium and get about 125 out.

The new units have a digital set point and are supposed to modulate better. Fwiw the unit in my system was making hot water in a rental for a year before I got it, and then it spent a year in the crate. I never counted on it lasting, it was an experiment that worked out well for me.

Highbeam · Oct 23, 2012

I've always liked your system fastback. How many watts is the titan? Also, to be clear, water circulates in a counterclockwise direction right?

kert · Oct 23, 2012

Fastback said:
It is the older version with a simple knob adjust so it does not show a range, but on high it sends 170-180 out. I run it between low and medium and get about 125 out.

The new units have a digital set point and are supposed to modulate better. Fwiw the unit in my system was making hot water in a rental for a year before I got it, and then it spent a year in the crate. I never counted on it lasting, it was an experiment that worked out well for me.

Thanks. I'm looking at using a titan for my setup. The price can't be beat.

philjafo · Oct 23, 2012

Fastback said:
I like cheap systems myself, but they have to work. What's the point of buying a car that gets 70mpg if it costs $70000.00, you can buy a lot of fuel for a cheap civic with the difference, you may not look as cool but you will get there.

My systems cost are spelled out for everyone to see, it heats 720 square feet to 65 degrees for an annual cost of under $400.

Would I try to heat a 4000sf shop with it, no that would be silly.....I would use four of them in independant zones lol.

You really don't need additional mixing pumps with this radiant design since you have adjustability in both flow rate and temperature. And once the floor is at a decent temp it really loafs along. This type of heater, when used as a traditional water heater, can take ground water in the wintertime and scald you with it, so turning 55 or 60 degree water up to 120 is no big load and if you get a close delta in your system it's capable of modulating itself down to a cost effective solution.

Just being a smarta$$, you left out the pressure guage between the heater and the spirovent.

koditten · Oct 23, 2012

I'm one that likes boilers, but I will say that you did put together a very good write up supporting water heaters. I will go as far to admit that a gas water heater is a good way to go. I just can't be convinced to use the tankless units. I've seen too many failures involving their use for domestic hot water. I just can't convince myself that technology has beefed up their durability.

I will say I'm biased, tho. I have boilers at work that are 50 or so years old and they show no sign of failing. I like those nuimbers.

Again, thanks for the write ups.

KO.

danski0224 · Oct 23, 2012

A standard vent tank type water heater at 40,000 btu's input is only 59% efficient, so you have 23,600 btu of heat available. The cheap ones are 34k btu.

Standard PVC vent tank water heaters are 62% efficient.

So, as long as the btu range works, and you don't mind thowing ~40 cents of every heating dollar up the chimney, there's nothing wrong with a water heater approach.

But, I'd for sure change the water heater T&P valve out for one appropriate for boiler use.

Highbeam · Oct 23, 2012

Check this out:

http://www.tanklessking.com/rheem-r...-heater.html?gclid=CNu99eCMmLMCFcV7QgodnQMArQ

So you can use the same 30 amp circuit that would power your electric water heater to deliver 100% efficient, 7kw, which is 23000 btu or so. 203$ no tax, no shipping, name brand and get your 20 degree rise at 2.5 gpm.

Why wouldn't this work? A tank around your heater doesn't get you anything except a cheap and big way to hold the electric elements.]

I'm not sure why it is that you can run a 29 amp device on a 30 amp max sized breaker. I always thought you had to oversize the breaker 25%.

Highbeam · Oct 23, 2012

danski0224 said:
So, as long as the btu range works, and you don't mind thowing ~40 cents of every heating dollar up the chimney, there's nothing wrong with a water heater approach.

Burning stuff is NEVER 100% efficient. This is reflected in cheap fuel prices. Electric costs more per btu but you get 100% or more of those btus delivered to the heating medium.

danski0224 · Oct 23, 2012

Highbeam said:
Burning stuff is NEVER 100% efficient. This is reflected in cheap fuel prices. Electric costs more per btu but you get 100% or more of those btus delivered to the heating medium.

Correct.

But, a standard atmospheric vent boiler is typically rated at 80% AFUE.

Low temperature radiant systems connected to a condensing boiler can approach 98% AFUE.

Either option is more efficient than a water heater if the funding is there to support the choice.

long handles · Oct 23, 2012

jlckmj said:
For those that have operating systems "ON THE CHEAP" (like me) feel free to explain it, also please please include a general idea of the cost of your system.

Jim

I've got $1200 in my system. Water heater,40gallon, direct vent, draws combustion air from outside. Flue in a flue setup. Outer flue combustion air, inner flue exhaust. Line voltage thermostat, taco pump. 1 zone.

A friend completed his shop a year before me. Just under 200sq ft larger than mine. $8K bill from contractor. Boiler for heat, + water heater for DHW. :headscrat

$6800 dollar difference between our systems.

Both do the same thing and the difference in gas usage between the two systems is not worth the extra $6800 he spent.

jlckmj · Oct 23, 2012

Danski0224,

First off let me start by saying that your opinion does matter to me. I have read some of your posts on this board and I feel that you genuinely try to assist people, and do so without getting on a high horse and talking down to them.

I am wondering if you read through the link I posted in my original post?

What is your opinion on the article re: the efficiency of the two systems?

I understand that a standard flue vent water heater is no where near the efficiency of a condensing boiler. But it does seem to me that the author posted some good arguments that the tank type water heater efficiency is under estimated, and the standard boiler efficiency is over rated. What do you think?

For the foreseeable future I am going to stick with my present game plan, but that does not mean I am unwilling to learn. Your statement below is the main reason, it is either work in the cold, or get something going on the cheap.

Either option is more efficient than a water heater if the funding is there to support the choice.

Thanks,
Jim

trythis · Oct 23, 2012

If your ceiling is tall, consider a radiant tube style heater. Cheaper and easier than radiant except it is radiant!, without the irritating blowing hot air.

danski0224 · Oct 24, 2012

jlckmj said:
I am wondering if you read through the link I posted in my original post?

What is your opinion on the article re: the efficiency of the two systems?

I glanced through it, and that guy appears to be doing some fuzzy math in the "efficiency" part.

The whole AFUE thing is a crock... but it gives a paper starting point.

If the water heater delivers enough btu's for the application, and if using a "water heater" as a "boiler" is allowed where you live, then go for it.

But there is a whole lot more to the whole "efficiency" thing, which includes sizing the loops properly and getting the GPM right to setting the combustion on the burner.

ddawg16 · Oct 24, 2012

While an electric heater might be '100%' effecient.....it is not that effecient....

When you compare the cost of putting x amount of BTU's into water.....the cost per BTU is much higher than gas.....

So far, gas water heaters are still your 'cheapest' way to heat water. If your constrained to eletric...then heat pump style water heaters are a much better way to go....on average, those heaters will heat up about 3-4x the amount of water as a typical resistive water heater.

So, while using the term 'effeciency' to describe eletric water heaters might be techincally correct, it is not accurate.

Highbeam · Oct 24, 2012

ddawg16 said:
While an electric heater might be '100%' effecient.....it is not that effecient....

When you compare the cost of putting x amount of BTU's into water.....the cost per BTU is much higher than gas.....

So far, gas water heaters are still your 'cheapest' way to heat water. If your constrained to eletric...then heat pump style water heaters are a much better way to go....on average, those heaters will heat up about 3-4x the amount of water as a typical resistive water heater.

So, while using the term 'effeciency' to describe eletric water heaters might be techincally correct, it is not accurate.

I think you were trying to say that electric heat is 100% efficient but not cost effective. Try bucking the old fashioned idea that electric is expensive.

Electric resistance heaters are indeed 100% efficient. They convert every single btu that is added to the system into heat in the water where a gas system loses some of the input energy into waste heat up the flue. This is a fact.

Despite this waste heat, gas can be cheaper IF your cost per btu of gas is very low as is usually the case with natural gas. Now if you are heating with propane, you are often money ahead to use electricity to heat the water. So, in simple terms, the efficiency of your heater matters and the cost of your input fuel matters. Use these factors in a calculator like this:

http://www.hearth.com/econtent/index.php/articles/fuel_cost_comparison_calculator/

to determine which fuel will be cheaper to use. You might just find that your old fashioned assumptions are wrong. You might just find that the better heating system is electric.

Then you can consider things like installation cost, maintenance cost, and convenience. In my region, electric resistance is cheaper to heat with than propane gas.

VHF · Oct 24, 2012

Highbeam said:
Electric resistance heaters are indeed 100% efficient. They convert every single btu that is added to the system into heat in the water where a gas system loses some of the input energy into waste heat up the flue. This is a fact.

This is true... at the point of use. But if you include generation (power plant) and transmission (line losses) as part of the picture then using electricity certainly isn't 100% efficent.

However, it could still be the most economical solution if the only alternative is propane. In my area propane vs. electric is about a wash, although propane prices certainly fluctuate more.

If natural gas is available, it is almost always a less expensive option as a heating fuel... even if the boiler/water heater is only 60% efficent.

Highbeam · Oct 24, 2012

VHF said:
This is true... at the point of use. But if you include generation (power plant) and transmission (line losses) as part of the picture then using electricity certainly isn't 100% efficent.

That's ridiculous. We are always concerned with the point of use being our garages. To include inefficiencies in production of the fuel at the original fuel production facility is inappropriate and completely meaningless, if you want to go down that road them you need to consider the exploration and mining costs of natural gas, how much energy did the drill rig expend to pump the fuel to the refinery?

Any inefficiency associated with the production of your fuel of choice is accounted for in the price you pay for the fuel at your point of use.

Electricity is the only fuel that can be more than 100% efficient. The heat pump systems are able to get better than 300% efficiency by using the metered electricity to draw environmental heat into your garage.

I like electricity because it is already being supplied to my home and I will be paying a bill for that nomatter what.

HoosierBuddy · Oct 24, 2012

Highbeam said:
I think you were trying to say that electric heat is 100% efficient but not cost effective. Try bucking the old fashioned idea that electric is expensive.

Electric resistance heaters are indeed 100% efficient. They convert every single btu that is added to the system into heat in the water where a gas system loses some of the input energy into waste heat up the flue. This is a fact.

Despite this waste heat, gas can be cheaper IF your cost per btu of gas is very low as is usually the case with natural gas. Now if you are heating with propane, you are often money ahead to use electricity to heat the water. So, in simple terms, the efficiency of your heater matters and the cost of your input fuel matters. Use these factors in a calculator like this:

http://www.hearth.com/econtent/index.php/articles/fuel_cost_comparison_calculator/

to determine which fuel will be cheaper to use. You might just find that your old fashioned assumptions are wrong. You might just find that the better heating system is electric.

Then you can consider things like installation cost, maintenance cost, and convenience. In my region, electric resistance is cheaper to heat with than propane gas.

The only reason electricity is ever more "efficient" than gas is because the efficiency for electricity is only considered from the meter in. You're ignoring the fact that electricity is generated somewhere (let's guess that's at an efficiency on the order of 60% depending on type of power plant, fuel, age, etc.) and moved down a transmission grid that is on the order of 90% efficient....meaning you've lost half the theoretical energy of the original fuel by the time it even gets to your meter.

So...by using power you're not only going from say $7/MMBTU gas to $30/MMBTU power, you're also wasting half the energy of the original fuel (and a great deal of that fuel is the same natural gas you've avoided using in your water heater) you are also doubling the greenhouse gas emissions of the system.

Think about it.

Phil

HoosierBuddy · Oct 24, 2012

Highbeam said:
That's ridiculous. We are always concerned with the point of use being our garages. To include inefficiencies in production of the fuel at the original fuel production facility is inappropriate and completely meaningless, if you want to go down that road them you need to consider the exploration and mining costs of natural gas, how much energy did the drill rig expend to pump the fuel to the refinery?

Any inefficiency associated with the production of your fuel of choice is accounted for in the price you pay for the fuel at your point of use.

Electricity is the only fuel that can be more than 100% efficient. The heat pump systems are able to get better than 300% efficiency by using the metered electricity to draw environmental heat into your garage.

I like electricity because it is already being supplied to my home and I will be paying a bill for that nomatter what.

You don't mine natural gas and it doesn't go to a refinery.

You drill a well, process it to remove impurities, put it in a pipeline, and move it to the end user via compressors and the whole system is more than 90% efficient.

And as I pointed out in my previous post...all of that happens anyway if your power is produced from natural gas. And since almost every power plant built in the last 15 years in the US has been natural gas fired...there's a reasonable chance that's where at least some of your power comes from.

BTW...this is a huge issue in the energy industry right now. Here's the gas side of it, if you are interested. I'm sure the power company might disagree:

http://www.aga.org/our-issues/energyefficiency/Pages/NaturalGasinaSmartEnergySystem.aspx

Phil

jvitez · Oct 24, 2012

HoosierBuddy said:
Think about it.

Phil

Well, the solution is simple then. Burn the coal directly to heat your garage. :eyecrazy:

Actually, that's only partly tongue-in-cheek. Our local coin-op car wash is heated with coal, purchased from our power company directly. He has a large hopper he fills twice a year, heats water for washing and for in-floor-radiant heating with a high efficiency boiler. He told me he saves at least $4000 a month vs NG. Only very rarely do I ever smell anything, and there is no soot.

There is no anthropogenic global warming. When do you ask judges to "rule" on the truth of science? The judicial ruling that carbon dioxide is pollution, and therefore able to be regulated by the EPA is politics and radical environmentalism at it's worst. It's junk science.

Anyway, I agree it does make sense to burn NG directly for heat instead of generating electricity with it, creating the efficiency losses, then using the electricity for heat. But it all depends on local costs and POCO issues.

We have hydroelectric generation here. Propane is currently 18% more expensive than electricity for heating, not including tank rental. Including that, it's 30% more expensive. Temporary heat for construction sites and BBQ tanks are the main uses here due to cost. Very few businesses or residences will use propane. Electric "boilers" are also very compact, silent, with no risk of CO poisoning. Not a bad combination actually.

NG is cheap now. Maybe not forever, but now for me it's about half the cost of electricity. Therefore, I will be using NG to heat my garage.

YMMV.

HoosierBuddy · Oct 25, 2012

jvitez said:
There is no anthropogenic global warming. When do you ask judges to "rule" on the truth of science? The judicial ruling that carbon dioxide is pollution, and therefore able to be regulated by the EPA is politics and radical environmentalism at it's worst. It's junk science.

YMMV.

I would go as far as saying "the jury is still out"...but that's pushing it. I understand that your mind is made up on the issue, but other reasonable people will argue the point.

Regardless, the EPA is regulating (as of this year) natural gas pipeline throughput and requiring gas companies and large gas consumers to convert their natural gas sales figures to "theoretical CO2 produced via combustion" in tons and report it as emissions. My theory is this is the first step in preparing for a carbon tax in the U.S....although every report I've seen regarding the political climate in Washington says a carbon tax is DOA in congress. The administration in power has great latitude in directing federal agencies (like the EPA) to regulate industry without new legislation though.

Personally, I've been so offended with even my limited interaction with the EPA regarding this new and ridiculous regulation that it has caused me to "back the other guy" this year.

As you stated very correctly "YMMV".

Phil

jlckmj · Oct 25, 2012

WOW, did we stray off topic a little?

Highbeam · Oct 25, 2012

None of that efficiency of production or delivery of any fuel matters at all. The only thing that matters when choosing a fuel source is cost per btu delivered and the efficiency of converting the input btus into output btus in my garage. I could care less if 1000 kittens were killed getting propane to my house.

Those are the two numbers you need. $ per btu, and % efficiency of the boiler.

So electric resistance boilers are 100% efficient at converting input btus into output btus. The cost of delivered electricity varies but in my area is cheaper than burning propane in a standard efficiency boiler. This makes resistance electric 100% efficient AND the most cost effective of standard technology.

So think about it, do I care how the electricity was produced? No. It is not a factor in choosing which fuel will heat my shop for the least amount of money.

Fastback · Oct 25, 2012

........

Fastback · Oct 25, 2012

philjafo said:
Just being a smarta$$, you left out the pressure guage between the heater and the spirovent.

I cant see the pressure changing any, its a closed system that runs at 120º max, heck I dont really need that pop off valve. I check system pressure with a tire gauge on the bottom of the expansion tank, and adjust it by adding air.

Highbeam said:
I've always liked your system fastback. How many watts is the titan? Also, to be clear, water circulates in a counterclockwise direction right?

I cant remember the specs off hand, its the same as the SCR2 heater, so google may give you a bunch of info.

Counterclockwise is correct, the red tape on the pex shows the hot side going into the floor.

BadgerBoilerMN · Oct 25, 2012

philjafo said:
It all comes down to using the right tool for the job, and usually the more a tool is needed to do the more it cost.

There you go. The bigger the job the more you can invest.

First, the heat load.
Second, the heat source (fuel).
Third, the boiler or water heater.
Then the system design.

philjafo · Oct 25, 2012

Fastback said:
I cant see the pressure changing any, its a closed system that runs at 120º max, heck I dont really need that pop off valve. I check system pressure with a tire gauge on the bottom of the expansion tank, and adjust it by adding air.

I cant remember the specs off hand, its the same as the SCR2 heater, so google may give you a bunch of info.

Counterclockwise is correct, the red tape on the pex shows the hot side going into the floor.

I meant you left out the price for the guage, I guess the one in the pic is a second temp guage. And yes you definitely do need that pressure relief valve as a safety feature if the electric water heater malfunctions and doesn't shut off at the set temp.

jlckmj · Oct 25, 2012

Fastback brings up a question I have been bouncing around in my empty head.

At what pressure do most of you guys run your systems?

I know the pressure tank came pre-charged at 12 lbs, so I have been leaving mine in that area. Right? or Wrong? or are they all different?

Jim

Dick in Wisconsin · Oct 25, 2012

jlckmj said:
WOW, did we stray off topic a little?

I was waiting for someone to bring up wind turbines! Hopefully we can stay on topic.

Fastback · Oct 25, 2012

philjafo said:
I meant you left out the price for the guage, I guess the one in the pic is a second temp guage. And yes you definitely do need that pressure relief valve as a safety feature if the electric water heater malfunctions and doesn't shut off at the set temp.

Ahh, yes, it's a temp gauge to show output.

I just put that pressure valve in to play it safe, for the low cost they should be used everywhere.

But, this heater needs to run really slow to even get to 175 at its max setting, much slower and it just turns off. It's a heater not a boiler, a traditional tank heater can overheat the contents and pressurize the vessel, but in this system the math is jut not there.

I run it fast enough that even if the tstat circuits fail the heater can't hit a dangorous temp. So I don't think my choice in a pop off is a practical one, it's more of a "just in case" valve that's really handy for belching out air during initial set up or service.

BadgerBoilerMN · Oct 26, 2012

Fastback said:
I like cheap systems myself, but they have to work. What's the point of buying a car that gets 70mpg if it costs $70000.00, you can buy a lot of fuel for a cheap civic with the difference, you may not look as cool but you will get there.

My systems cost are spelled out for everyone to see, it heats 720 square feet to 65 degrees for an annual cost of under $400.

Would I try to heat a 4000sf shop with it, no that would be silly.....I would use four of them in independant zones lol.

You really don't need additional mixing pumps with this radiant design since you have adjustability in both flow rate and temperature. And once the floor is at a decent temp it really loafs along. This type of heater, when used as a traditional water heater, can take ground water in the wintertime and scald you with it, so turning 55 or 60 degree water up to 120 is no big load and if you get a close delta in your system it's capable of modulating itself down to a cost effective solution.

Say now, Fasty, that is a nice looking system.

When "bad-mouthing tank-less water heater use for space heating I was referring to gas-fired tank-water heaters. For small spaces where reasonable electricity can be had, your system is what I would use. You don't need a mixing valve, combustion air, gas, or "fancy" designs.

The line voltage stat is classic simplicity.

Well done.

BadgerBoilerMN · Oct 26, 2012

Fastback said:
I dont really need that pop off valve. I check system pressure with a tire gauge on the bottom of the expansion tank, and adjust it by adding air.=QUOTE]

You know how I hate to disagree but. The relief may not be "needed" in your particular system as there is very little water to expand to 1700 times its original volume, but should someone have a conventional tank-type water heater (equivalent to about a half stick of dynamite) they might get the wrong impression.

The other thing to keep in mind about pressure relief valve (PRV) is that they will blow off when the expansion tank has failed or the heat source is stuck on until steam is made. In this case the PEX may melt down giving any nearby occupant a steam bath.

Finally, you can guess at the system pressure but you can't find it reliably from the air-side of the expansion tank, since the air pressure will change as the system temperature rises. If the water pressure in the system changes the air pressure goes up and down to compensate for the expansion.

If you fill the system to a static (no pumps on) pressure of 12psi and find it later at 10psi you have lost air in solution and must replace it with water. If you recharge the expansion tank (the pressure of which must match the system static water pressure) you will be limiting the capacity of the expansion tank and at some point may blow of the PRV.

The only thing I would add to the system is a fill valve between expansion tank and system connection and yes a Tridicator that would show temperature and pressure, dare I say, like a regular boiler.

PeterT · Oct 26, 2012

Fastback said:
I like cheap systems myself, but they have to work. What's the point of buying a car that gets 70mpg if it costs $70000.00, you can buy a lot of fuel for a cheap civic with the difference, you may not look as cool but you will get there.

My systems cost are spelled out for everyone to see, it heats 720 square feet to 65 degrees for an annual cost of under $400.

Would I try to heat a 4000sf shop with it, no that would be silly.....I would use four of them in independant zones lol.

You really don't need additional mixing pumps with this radiant design since you have adjustability in both flow rate and temperature. And once the floor is at a decent temp it really loafs along. This type of heater, when used as a traditional water heater, can take ground water in the wintertime and scald you with it, so turning 55 or 60 degree water up to 120 is no big load and if you get a close delta in your system it's capable of modulating itself down to a cost effective solution.

That is excellent pictorial.

Thanks a bunch, I learned something new today already. :pimpflash

BadgerBoilerMN · Oct 26, 2012

I would like to say Highbeam has made his point.

It is not that electricity is good or bad, it is just electricity. I have installed high efficiency condensing boilers for a few decades now, in fact the very first one was installed to replace an electric baseboard system. But when the local power company offered me power at 4 cents kW I installed an electric boiler.

It is a shame to use such a refined product in such a crude fashion as with a resistance element, much like Edison's first light bulb, but if we trust in the free market and use hydronics as the heat transfer terminal the market will sort itself out and we can change our minds if we must.

Highbeam · Oct 26, 2012

Thanks Badger, and you bring up another issue.

It seems that all of these tankless designs, whether they use gas or electric, boiler or water heater, they all seem very modular. The heating device is really very replacable should it fail or should you decide to change it for other reasons. It is very easy to slap in a 164$ rheem 13KW water heater and feed it with an 8gauge 40 amp oven circuit. The 13 kw is nearly triple the output of domestic tank water heaters that people seem to think are adequate and takes up way less space and cost. Don't be afraid to try electric tankless water heaters. You won't break the bank with equipment costs. If your electric is expensive you may break the bank with energy costs though.

Even the circ pumps are easily changable. The only decision that you are pretty well stuck with is the pex in the slab.

Boiler vs. Tankless vs. Tank type water heater

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