Radiant heating

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fozzy12

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I am building a 30 x 36 garage. It's 2 x 6 construction with attic trusses. I end up with an 18 x 30 room upstairs. I am putting radiant tubing in the slab and also under the second floor sheeting. I bought the system from a supplier in VT. They are well known. I need a hot water heater that has an output BTU rating of 40K. That is figured by input BTU times efficiency. When I looked around the big box stores, they don't have anything. I checked Rheem and Ruud and they have one although it's a 75 gallon unit. When I called my local plumbing supply, they told me what I was doing wasn't legal. Said in Michigan you aren't allowed to do that with a water heater. This is a closed system, there is no water in the garage. It is not going to be used for anything else. They tell me I need a real boiler to do this. The company disagrees. I have a phone call into the inspector now to figure out what to do. Any thoughts out there?

Thanks
Eric
 

jadnashua

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Using the proper backflow preventers and safety features, it would probably work. Personal opinion, a WH is not designed for continuous use like what would happen during a heating season and you'll probably wear the thing out. A commercial unit might be rated for a higher duty cycle, but again, a boiler is designed to run continuously, a WH is not, so your life expectancy may be low.
 

NHmaster

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Why would you want to go to all the expense and effort of installing radiant heat just to use an inefficient tank heater to drive it? Heating 40 gallons of water or more makes no sense from an efficiency standpoint at all. Do yourself a favor and find a high efficiency Mod Con boiler.
 

Paso One

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I did exactly what you are proposing.

I had a 18 x 30 building attached to my 30 x 30 gas heated shop.

In the 18 x 30 building I have 2 zones with approx 200 ft per zone.

It is heated with 2 40 gallon electric water heaters.

The first year I used only one water heater but I found when the tempetures got to -40 for a week at a time the one 40 gallon was working all the time.

Now with the second unit dumping into the first they are off most of the time.

Shop is warm all the time.

It is illegel around here I believe as well but it has been working flawless.

I went this way only because I wanted a "ignition free " area to paint in.

Don't be turned off your idea it does work. ( 5 yrs now )
 

comp1911

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I was told by my electrical inspector that the equipment needs to be UL listed for heating service. This was in MN.
 

Enosez

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I did exactly what you are proposing.

What water temp are you running through your zones?
And are you using a manifold?

Here in NY it would cost a fortune to running anything electric let alone during a cold spell.

I considered it also for a 900 square foot garage but in the end operating costs made it cheaper to go with a boiler.
 

NHmaster

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Here's a pile of other issues also. The slab will want water temps around 85 degrees, the staple up around 160 or perhaps more depending on the substrate and floor coverings. Running an electric water heater at those temperatures will cost a fortune and require a mixing valve for the slab heat. I've seen this done several times before and it has never worked out. The water tank is usually swapped for a boiler of some sort within two years.
 

Paso One

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I did exactly what you are proposing.

What water temp are you running through your zones?
And are you using a manifold?

Here in NY it would cost a fortune to running anything electric let alone during a cold spell.

I considered it also for a 900 square foot garage but in the end operating costs made it cheaper to go with a boiler.

I have 2 zones (see pic) temp tonight is about 130 degrees outside tempature is 20 degree f
 

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NHmaster

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If you are running 130 through the slab your cement will crack, powder and fail within a couple of years. Never more than 95 degrees maximum.
 

Enosez

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If thats daylight coming through the outside perimeter wall , I'd think about putting insulation there. (Heat loss to outside)
Also all of your loops are uniform, without an exterior zone loop which is usually closer together since more heat loss is at exterior walls.
 

Paso One

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The outside "daylite" you see is actually the aluminum air foil going up the wall.

The concrete hasn't cracked yet But concrete in this area always cracks so It is going to happen anyway. No sign of powerdering at all. ( 5th winter )

My water tank is set at 130 degrees but I'm sure it is less going thru the slab.

I'll try it set lower. I park a bobcat in the area so it heats the steel and is nice and toasty when needed.

This is the first I heard of the max 95 in concrete.

Around here people heat the driveway to melt the snow so perimeter heating is a moot point. ( my loop melts outside threshold )
 

Bill Arden

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Why would you want to go to all the expense and effort of installing radiant heat just to use an inefficient tank heater to drive it? Heating 40 gallons of water or more makes no sense from an efficiency standpoint at all. Do yourself a favor and find a high efficiency Mod Con boiler.

Because it's cheep and a lot easier to upgrade in the future.

Electric boilers have gotten cheaper so using a hot water heater is not saving very much.
 

Frenchie

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If the "well-kinown supplier in vermont" is who I think it is, you need to STOP what you're doing. Those guys are notorious for half-assed advice, badly designed systems, they're just very good at "image control" on the internet.

Go to the forums at heatinghelp.com, do a search on that forum for the supplier's name. Stick around for a bit, over there, lotsa good info on designing a proper radiant system. Other good sources: radiant panel association, radnet, warmly yours.
 

NHmaster

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Having designed and installed more radiant systems than I can even begin to recall in the past 25 years or so, it makes me scratch my head when I read threads like this. There is always someone that can and will justify almost any half assed combination for either price or expediancy reasons. Just because you have been running 130 degrees for 5 years now without a catastrophic failure you think that it must be ok and those of us that design and install for a living (and back it up) must be wrong and or overly cautious. So keep on keeping on, and when the you know what hits the fan be sure and not bother to tell those of us who will say " I told you so"
 

smokinjoe

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Having designed and installed more radiant systems than I can even begin to recall in the past 25 years or so, it makes me scratch my head when I read threads like this. There is always someone that can and will justify almost any half assed combination for either price or expediancy reasons. Just because you have been running 130 degrees for 5 years now without a catastrophic failure you think that it must be ok and those of us that design and install for a living (and back it up) must be wrong and or overly cautious. So keep on keeping on, and when the you know what hits the fan be sure and not bother to tell those of us who will say " I told you so"

You are always to the point..I for one appreciate your inpu on here...Thank u..:)
 

NHmaster

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Well I guess that makes you the current expert on the matter. So if you don't mind dancing around on a 150 degree floor then by all means go for it. The rest of us however will be content to design radiant systems that use water temperatures that are comfortable for human occupation.
 

Bill Arden

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Well the way my solar hydronic systems works, the floor warms up, the heat transfers to the air space and the thermostat reaches it's set temp, and turns that zone off. The floor in my bathrooms (tile) may reach 90-95 degrees before the thermostat, set at 75, turns off that zone. Floor Temp needs to be higher than about 90 degrees before it feels warm to the touch, so no problem with 150 degree floors in my house.
Witch

I am going to translate that as saying "I don't have a problem with hot floors since the floor itself does not get that hot"

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I'm playing around with a non UL approved "research" set up as well.

Here's what I've got so far
1. A bronze recirculation pump
2. In floor PEX
3. A plastic non-pressurized tank. (open air system)
4. Plans for a solar trough that will still work at -40F.
5. Two 50 gallon hot water heaters with internal 30sq heat exchangers.

I have to use copper, PEX, or brass for corrosion reasons. (open air)

It is legal to use a hot water heater to heat potable water and then use that to heat the floor via a heat exchanger.

It is also legal to use the hot water to directly heat the floor, but that means there is no way to use antifreeze.

Note: to stay legal, you would have to have some sort of sink to justify having the hot water heater there and to use some water. I would also recommend adding a check valve before such a long and possibly "stale" section of water pipes.

To stay safe you have to have a "safety" expansion tank on the potable water side AND use non-toxic antifreeze on the heat side.

One reason they don't like hot water heaters being used for in floor heating is that you can not use antifreeze with a hot water heater since even the fold back elements tend to scorch and burn the antifreeze.

Electric boilers designed for heating are carefully designed to maintain fast water flow past the elements and this keeps the element surface temp below the point where the antifreeze starts to degrade.

I could build my own boiler that would be safe, but is it really worth my time.
 

NHmaster

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What?

Are the damned floors 150 degrees or not? Not a complicated question I think.

If you want to use an electric water heater than by all means go right ahead. You are the one paying the bill. However all you cowboys need to understand that there are mechanical codes that regulate the installation of all heating systems and to insure that your insurance will pay off when the house floods or burns down, you need to get the system inspected and signed off.
 
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