Advice for in floor heat design

[alanf]

I am building a 54' x 32' workshop in central Vancouver Island B.C. It will be 2x6 construction, concrete foundation/stem wall/slab. I plan on insulating the walls (R19), the ceiling I would think R28 or so and R10-12 under the slab. I would like to do radiant heating, will also be building a bathroom in the shop also, so would like domestic hot water also. Can I use a natural gas fired hot water heater to do both workshop domestic hot water and the radiant heat? I have done a bunch of reading in this forum, but haven't found the info needed to do my own design / install. Can anyone offer me advice on where to look for design (parts etc) info either on this forum or elsewhere?
Thanks,
Alan

 

[deckmonkey]

Possibly. Winter temps are pretty mild there, correct? How many people in the house? It would have to be a pretty large tank, 60 gal at least. You would need a heat exchanger,pumps, controls, etc. Basic info should be online or ask at the wholesaler about it.

 

[alanf]

I have been looking at the radiantec website, interested in the open direct system. This system does not use a heat exchanger, the hot water heater delivers warm water to the radiant tube in slab, and if you want hot tap water, it is pulled directly out of the system. Seems to be a relatively simple system. It does not use a heat exchanger or flow glycol through the radiant tube. It does not get particularly cold here on the island, but I suppose the drawback is you would have to keep the system running during a cold snap or risk freezing the water in the pipes. I would only need hot water for handwashing etc, not really to be used as potable water (hot) as it is a shop not a home.

 

[deckmonkey]

They run a similar system in some of the townhouses around here but with baseboard. One of the issues is stagnant water in the summer in the piping. Also an open system lets oxygen in which can erode the metal piping and fittings. I think you would have to have a bypass or a mixing valve to draw water from the tank or it would be a long time to get really hot water if the floor is calling for heat.

In my buddy's new house he set it up so the well water goes through the floor to preheat it before the Rinnai and mixes in hot water to heat the floor as well. Not sure what his piping layout is. The upside should be cooling in the summer.

 

[finn]

Check your local codes.

Open systems were somewhat common at one time but seem to have fallen out of favor because of the possibility of providing a breeding ground for Legionnaires disease, among other issues.

They now don't meet code in some locals.

 

[efncrx]

Couple of questions,

1) How much hot water do you need for your bathroom? Just hand washing? Or will there be a shower?

2)How often will you use hot water?

I put a bathroom in my 24x48 garage, just a toilet and utility sink, ran pex tubing through 2" pvc 6' deep in the ground into my basement and tied it into my water supply with an on off ball valve. I'm in Minnesota and we can get some really cold winters! If my in floor radiant ever goes out, I add antifreeze in the toilet and shut off the water supply in the basement to avoid freezing and cracking plumbing.

As for my hot water picked up a 10gallon 110v electric water heater (less than $100, and really small footprint of space taken up) plumbed with leftover pex. I spent $300 total on the bathroom scrounging craigslist for scrap materials/toilet/laundry sink ect only bought some fittings, pex crimper, and water heater. Going on 3.5 years now and not one problem.

 

[alanf]

Thanks for the replies. I will definitely check the local codes not point considering a system if it will not be allowed anyway. Efncrx, I don't imagine I will be using much hot water, no shower planned, just washing hands etc. I wonder if it makes a difference code wise if the hot water would not actually be potable? If I make tea or coffee, I would be boiling cold water anyway....

 

[Jess]

Did you have a heat load calculation done? You could ask at the local Andrew Sheret outlet if they will do one for you. A few years ago, there was one of the staff at Campbell River that did them. Ask at the others. They also have all the necessary Wirsbo Heat pex, manifolds etc. and can put together a package for you. Don't be afraid to ask for a preferred price since you would be buying it all from them. For warranty reasons, they will not sell gas stuff outside of the trade but you can get info from them and have a friendly local licensed guy supply and commission it for warranty purposes. When I built my shop, I put 2" foam under the floor, lots of rebar, mesh on top and then zap strapped the pex to the mesh. 5" pour and kept wet for a couple of weeks to aid in cure. Keep the run lengths the same, spaced closer near the outside walls and door where loss will be greater. be sure to place a thermal break foam strip all around the slab at the walls as that is where you will have loss. Beside good insulation practises, be sure to air seal everything to eliminate loss. I can't offer any suggestions for your hot water other than to look at a plate heat exchanger to separate the two parts. Good luck with you build...

 

[alanf]

I stopped in at Andrew Sheret this morning to ask about radiant heat options. I was told that a domestic hot water heater would not be able to provide enough btu's to do the job, and that an on demand water heater is just not designed for this application. The fellow suggested an Eco King combi boiler for this application. Pretty pricey at $3100 Can, but it will certainly provide for radiant heat and plenty of hot water for a sink. They offered to do a heat load calc for $150, but I said not to do that yet, as I am still trying to get a feel for prices compared to ordering online from someone like Blueridge supply. While the initial cost is a bit steep with the combi boiler, initial online research suggests that the lifespan of a boiler will far exceed the life of an on demand or tank style heater. The unit that was recommended to me was the Eco-King C100 combi boiler..... anyone have any experience with this unit? The combi boiler incorporates an expansion tank, is fully modulating and has a 95% AFUE. It seems like this unit would replace a few of the components needed to do a heating system, so a few dollars saved there. It seems like this type of unit with its high efficiency would make future heating bills as reasonable as possible. I haven't asked for a discount yet, so hope we can sharpen the pencil somewhat over my initial quote.

 

[James-W]

I don't understand why so many people want to use a water heater for their hot water heat system instead of a boiler which is designed for such an application. That's like wanting an epoxy floor but not wanting to pay for a really good grade of epoxy so you get some inferior product and put it down on the floor instead. In-floor heat is a wonderful way to heat the space, but don't scrimp on the water heating unit. Get a boiler designed for that purpose and it will work flawlessly for many years to come.

 

[Randy in Maine]

I have one of these that supplies 3 zones (2 in the house and one in the garage) + my domestic hot water. Works great and does it very efficiently.

http://www.wallhungboilers.com/prod_baxi_condensing_380.html

 

[Radiantec Guy]

Hi Alan, if you will only use the system sporadically then I would recommend going with a closed loop system where you put in glycol for freeze protection.

 

[HoosierBuddy]

I don't understand why so many people want to use a water heater for their hot water heat system instead of a boiler which is designed for such an application. That's like wanting an epoxy floor but not wanting to pay for a really good grade of epoxy so you get some inferior product and put it down on the floor instead. In-floor heat is a wonderful way to heat the space, but don't scrimp on the water heating unit. Get a boiler designed for that purpose and it will work flawlessly for many years to come.

Agree. The combi-boiler is the correct type of appliance for your application.

Phil

 

[Radiantec Guy]

Alan, since you want domestic water for a sink only, you should go with either a closed system or indirect which uses a heat exchanger to separate the heating from the domestic.

Probably the most economical choice would be the closed system where you would purchase a separate but small domestic water heater for the sink. The small 10 gallon water heaters are relatively cheap. The extra cost associated with installing the heat exchanger and associated components can be as much as $800.

One last option is to go with a combi-boiler. These have separate chambers, one for heating and one for domestic but they can be somewhat pricey.

 

[Chris705]

http://content.zurn.com/web_documents/pdfs/RadiantInstructions.pdf
http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_12_0.pdf
The above links have been very helpful to me in making a decision about which heating plant I need to use. I have performed multiple heat loss calculations using various on-line programs and all come fairly close to each other so I think I can properly size my condensing wall hung combination boiler.....I urge you to carefully go thru various heat loss calculations as you read thru the above it will help you fully understand radiant heating so you can be informed to make decisions and pursue the equipment you want. I am sure the local supplies like their certain line of equipment and you can jot these down and do your own research to make sure they are going to work. These links will also help you learn how to calculate what size pumps you will need....Good luck with your build!

http://www.caleffi.com/usa/en-us/technical-magazine

 

[bzinsky]

I don't understand why so many people want to use a water heater .

Because they are cheap, efficient, simple, easy to replace, are designed to operate at the water temps commonly used with in-floor radiant heat

 

[bzinsky]

would never use a combo boiler for this application, that is a ludicrous waste of money to supply a single bath sink.

Small electric water heater definitely, just separate it from the system.

 

[Radix2]

Because they are cheap, efficient, simple, easy to replace, are designed to operate at the water temps commonly used with in-floor radiant heat

Not really, and this is a criticism of the otherwise excellent documentation the radiantec guys put out.

The cheap simple gas water heaters are NOT designed to operate at temps commonly used for in-floor heat. Sure, if given enough time and power you could say that the 120-140 temp that they are designed for is compatible with in floor - but in reality when using these systems to heat shops and such, you have ambient temps say around 65 and many times cold slabs to bring up.

So there is a lot of time with return water which will bring the tank temp down m well below the set point, and there will condensation in the flue, which these cheap tanks cannot tolerate.

My beef with radiantec is that they talk about low return water as not a problem, but they correctly recommend very nice condensing tank type heaters - which are not the cheapies people are thinking of - $3000-4000 for those Polaris tanks in the pictures!

The other beef is that they name return water temps as a problem for boilers, when that is only the case for old style non condensing boilers, whereas modern high efficiency boilers absolutely love operating at low temps, where they are most efficient.

 

[Radix2]

would never use a combo boiler for this application, that is a ludicrous waste of money to supply a single bath sink.

Small electric water heater definitely, just separate it from the system.

Yep!

 

[bzinsky]

Not really, and this is a criticism of the otherwise excellent documentation the radiantec guys put out.

The cheap simple gas water heaters are NOT designed to operate at temps commonly used for in-floor heat. Sure, if given enough time and power you could say that the 120-140 temp that they are designed for is compatible with in floor - but in reality when using these systems to heat shops and such, you have ambient temps say around 65 and many times cold slabs to bring up.

So there is a lot of time with return water which will bring the tank temp down m well below the set point, and there will condensation in the flue, which these cheap tanks cannot tolerate.

My beef with radiantec is that they talk about low return water as not a problem, but they correctly recommend very nice condensing tank type heaters - which are not the cheapies people are thinking of - $3000-4000 for those Polaris tanks in the pictures!

The other beef is that they name return water temps as a problem for boilers, when that is only the case for old style non condensing boilers, whereas modern high efficiency boilers absolutely love operating at low temps, where they are most efficient.

I wasn't trying to make an argument on water heater vs boiler, I was simply stating that water heaters are viable, simple, cost effective solutions.

One thing to keep in mind about this, is we're talking about garages and shops here. All the precision and reliability we demand from whatever heats our home is usually not as critical in the shop.

 

[Radiantec Guy]

Water heaters are actually designed to put out water at 120-130 and have supply water as low as 40 degrees. Where we're located in VT, the water from our wells is typically that cold in the winter. The risk of condensation is actually greater when used for domestic water than with a radiant system. In a radiant system, even if the slab is 40 degrees, the returning water temperature will be significantly warmer than this. Our experience in this condition will be for the returning water to be 40-50 degrees cooler than the outgoing upon initial start-up in a cold slab which is much warmer than when this heater is used for domestic purposes.

We do worry about cold return temps to non-condensing boilers because condensation actually happens in the tank and will cause the cast iron tank to prematurely fail. As Radix2 mentions, this isn't as big of an issue with the newer condensing style. Water heaters, with their stainless, ceramic, or glass lined tanks can withstand the lower return temps and any condensation that may occur.

I'm not saying an inexpensive water heater is the way to go in all situations but since we've been in business so long, we've had thousands of customers use them with great success under the right scenario. Also, we set up many systems using boilers. I don't want to push anyone in any direction and only speak from our experience as to what works for us and what doesn't.

 

[Radix2]

Water heaters are actually designed to put out water at 120-130 and have supply water as low as 40 degrees. Where we're located in VT, the water from our wells is typically that cold in the winter. The risk of condensation is actually greater when used for domestic water than with a radiant system. In a radiant system, even if the slab is 40 degrees, the returning water temperature will be significantly warmer than this. Our experience in this condition will be for the returning water to be 40-50 degrees cooler than the outgoing upon initial start-up in a cold slab which is much warmer than when this heater is used for domestic purposes.

We do worry about cold return temps to non-condensing boilers because condensation actually happens in the tank and will cause the cast iron tank to prematurely fail. As Radix2 mentions, this isn't as big of an issue with the newer condensing style. Water heaters, with their stainless, ceramic, or glass lined tanks can withstand the lower return temps and any condensation that may occur.

I'm not saying an inexpensive water heater is the way to go in all situations but since we've been in business so long, we've had thousands of customers use them with great success under the right scenario. Also, we set up many systems using boilers. I don't want to push anyone in any direction and only speak from our experience as to what works for us and what doesn't.

Talking about return temps from radiant vs groundwater temps for DHW misses the point I think.

Most of the time we use DHW, we do not use enough to drop the tank temp much below the set point - so the cold water coming in is not a issue. Sure, for the times the kids run the water out or the like, the flue will condense until the water is over the dewpoint and then it will stop until the next time - the duration is limited by the 50 gallons to be heated and the time between shower marathons...


It is a different story for radiant floors where the mass to be heated is many tons of concrete. In that case, you can have return temps well below the dewpoint for hours and hours - the heater is not just bringing 40-50 gallons of water up, but must bring tons of concrete as well before your tank and return water is back up to the 100-110deg required to stop condensing.

And again we are talking about the cheap $400 tank heater here - it doesn't matter if it is glass lined, the flue and burner assembly is plain steel and rusts very easily under the drip sizzle you get when they condense.

I absolutely agree with you that your Polaris tanks or all stainless models could be very good heat sources, but lets make it clear that your basic 6year water heater from the box store is not going to take it well.


the other issue I see with open systems is that while the tank itself is lined to withstand the oxygen in the input water - what about the cast iron pumps ? Do you recommend bronze or SS units or is it not really an issue?

The purpose of the pex barrier pipe and closed systems is not just to protect the heat source, but all the iron and steel components.

 

[Radiantec Guy]

Talking about return temps from radiant vs groundwater temps for DHW misses the point I think.

Most of the time we use DHW, we do not use enough to drop the tank temp much below the set point - so the cold water coming in is not a issue. Sure, for the times the kids run the water out or the like, the flue will condense until the water is over the dewpoint and then it will stop until the next time - the duration is limited by the 50 gallons to be heated and the time between shower marathons...


It is a different story for radiant floors where the mass to be heated is many tons of concrete. In that case, you can have return temps well below the dewpoint for hours and hours - the heater is not just bringing 40-50 gallons of water up, but must bring tons of concrete as well before your tank and return water is back up to the 100-110deg required to stop condensing.

And again we are talking about the cheap $400 tank heater here - it doesn't matter if it is glass lined, the flue and burner assembly is plain steel and rusts very easily under the drip sizzle you get when they condense.

I absolutely agree with you that your Polaris tanks or all stainless models could be very good heat sources, but lets make it clear that your basic 6year water heater from the box store is not going to take it well.


the other issue I see with open systems is that while the tank itself is lined to withstand the oxygen in the input water - what about the cast iron pumps ? Do you recommend bronze or SS units or is it not really an issue?

The purpose of the pex barrier pipe and closed systems is not just to protect the heat source, but all the iron and steel components.

Good points Radix. In this type of system everything needs to be potable rated so stainless or bronze pumps are mandatory.

I don't disagree with much of what you say other than high-efficiency boilers and water heaters are out of many peoples price range. Standard water heaters do work. As an example, I have 3 family members with this system using standard power-vent water heaters. One has been in operation 11 years, another 8, and the last 5 years. These heaters cost about 1/4 of the Polaris or a high efficiency boiler so even if they failed tomorrow they are still way ahead in terms of cost. Now this isn't counting the difference in efficiency and operational cost but not everyone can afford these or cares about operational costs; upfront installation cost is what many of our customers are worried about.

Back to the Polaris for a minute. What makes this a good choice for many applications is its high heating output which the standard water heaters do not have.

Good discussion!

 

[bzinsky]

speaking of power vents, man do they work well, I just installed one in my own home about a year ago.

50 gallon, 40k btu. Wife left the shower on by accident once for 8 hours (long story)
Somehow, someway, the science does not say this is possible, but it was still pumping out comfortably warm water after 8 hours. I didn't think 40k btu's was capable of heating water on demand like that.

The previous HWH I took out, when it ran out of hot water, it really ran out of hot water, ice cold. I really don't believe the efficiency ratings after that. There is no way the power vent is only 10-15% more efficient at transferring flame energy to the water, or whatever they rate them at. With the same btu input rating, the output difference between the two was massive.