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Old 10-09-2009, 02:30 PM   #1
Steve1
 
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infloor hot water


In a new addition of about 600 sqft I installed 2 loops of pex in the concrete for hot water circulation. It is not the primary source of heat(forced air heat pump) but to warm the floors. I need to know if a tankless hot water heater will be enough to supply the system and if so how big? ie. how many amps? I have a 30 amp circuit available and can purchase a wall mount 3 loop control system with pump, exp tank, etc. I've been told that the smallest wall boiler is too much for a small system like this. Any thoughts?

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Old 10-09-2009, 04:20 PM   #2
An old Tradesmen
 
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infloor hot water


Depends how warm you want the floor. And how well you insulated teh floor.

30 amps isn't gonna give you much heat.
And, can be expensive to operate.

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Old 10-09-2009, 04:58 PM   #3
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infloor hot water


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Originally Posted by beenthere View Post
Depends how warm you want the floor. And how well you insulated teh floor.

30 amps isn't gonna give you much heat.
And, can be expensive to operate.

I can probably go to a 50 amp breaker The concrete has 2" foam insulation under it. I have a 200 amp panel but I am running a 2.5 ton heat pump with backup electric furnace plus the rest of the house. I mainly want to warm the concrete floor not heat the room.
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Old 10-09-2009, 05:55 PM   #4
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infloor hot water


It takes a lot of heat, to even just warm concrete.

What flow rate did you design the loop for? And at what water temp?

You may need to go to 50 amps. You'll get between 32,00 and 35,000 BTUs of heat. A good part of that heat will still be drawn toward the ground.
And if you have no perimeter insulation, a fair amount will be lost there also.

So you'll probably want a heater that has 10KW of heaters in it. Which would require a 50 amp feed.
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Old 10-09-2009, 06:20 PM   #5
Steve1
 
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infloor hot water


From what I understand the water temp should be about 85, wall insulation is Insulated concrete forms(about 6" of styrofoam + the concrete) should be easy to heat, flow rate I'm not sure, about 500' of 1/2 " pex in 2 loops which I'm told is very small.
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Old 10-09-2009, 06:34 PM   #6
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infloor hot water


Gonna take a high water flow. 85 water temp. Might take 4 days to warm the concrete. When first turned on.
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Old 10-09-2009, 06:53 PM   #7
Steve1
 
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infloor hot water


Yes from what I'm told the power demand drops alot after the initial heat, that's why I'm hoping to do it with a water heater. I've had people tell me to use a tank type water heater but they're not as efficient as a wall mount so I was hoping to be able to use one of them. I looked into a wall mount boiler but most can't be turned down enough for a system that small.
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Old 10-09-2009, 07:02 PM   #8
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infloor hot water


Only efficiency difference between a tanked electric water heater, and a tankless. Is the tankless has no standby loss.

Which doesn't add up to much.
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Old 10-09-2009, 07:03 PM   #9
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infloor hot water


I know that I heated a about 2000 ft2 of building with floor heating is a concrete slab, with minimal insulation using a natural gas tank type hot water heater, with temps down to -35 with good results. This room was used as a classroom with no complaints. I ran the water @ 110F with a standard home boiler circulator pump. When I installed a conventional boiler my fuel bills increased big time. As stated, maintaining heat is much easier than the intial start-up, but is your floor all that cold now?

I think the instant tank should work great, have seen some in newer houses in Southern Alberta.
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Old 10-09-2009, 07:16 PM   #10
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infloor hot water


No it's not that cold but a little warmth in the floor in a basement makes a big difference in the comfort level, it will be mainly a TV room so I want to be comfy in my lazyboy. There is quite a difference in cost between a tank type and tankless and as I said I can buy a wall mount control panel with pump and expansion tank, controls etc.

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