Radiant Floor Heating Question

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Old 02-12-14, 06:21 PM
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Radiant Floor Heating Question

I have a room that is about 1050 sq/ft. When we poured the concrete floor we put water pipes in it for radiant heating. We currently have a wood burning furnace/boiler but after several chimney fires and several trips to the basement to reload we decided we want to go with something more safe and practical.

1. My house is back in the woods so I guess electric, propane, and oil are my only power source options? Electric would be preferred if there was one that didn't cost a fortune to run.

2. Can a water heater or tankless water heater do the job or does it have to be a boiler?

3. Are there certain terms I should use when sourcing these because to just type "boiler" in google brings up a lot of regular ole water heaters?

4. Anything else a DIY-er should know on these?
 
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Old 02-13-14, 01:00 AM
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When we poured the concrete floor we put water pipes in it for radiant heating.
What kind of "water pipes"? Unless you used PEX with an oxygen barrier you will have problems. Steel piping will have to be chemically treated to prevent corrosion. Copper piping will likely corrode from the outside although that could takes decades. If you used regular PEX then oxygen will diffuse through the walls of the tubing and make the water corrosive. In this case you have to use all non-ferrous piping along with pumps in the system or else use chemical treatment and maybe even a heat exchanger between the radiant slab and the heat producer.

Most stand-alone domestic water heaters are not "listed" for use in space heating applications although there ARE a few that are so listed.

Radiant is easy to do but difficult to do correctly. Did you properly allow for ground water removal under the slab? Did you properly insulate under the slab and most importantly insulate between the slab and any footings/foundations and walls? What size tubing (diameter) and the lengths of the individual tubing loops did you use? Did yo do a heat loss calculation on the building and then size the radiant loops to that calculation?
 
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Old 02-13-14, 06:13 AM
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We had a professional who dealt in these things install everything when the house was built in 1987. I don't know what he used but I have no doubt that he did everything he was supposed to with the materials that were available at that time. The pipes that connect to my current boiler are copper and look to be about 2" diameter.

1. My house is back in the woods so I guess electric, propane, and oil are my only power source options? Electric would be preferred if there was one that didn't cost a fortune to run.

3. Are there certain terms I should use when sourcing these because to just type "boiler" in google brings up a lot of regular ole water heaters?

5. How do I go about calculating the model of boiler that I would need?
 
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Old 02-27-14, 06:33 AM
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Power options will vary depending on what you can gain access to . You may want to consult with a professional as to what power options you have and what would be the most economical.
 
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Old 02-27-14, 04:07 PM
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are you in florida ?
If so your heating requirement s are not too great.
A combi core (bradford white) would work.
There are a number of electric boilers on the market.
Also an air to water heat pump would also work.

The question becomes how much money do you want to send up front vs running costs. A combi core installation is going to be a low up front cost, but since propane is not so cheap these days it will cost more in the long run. I think electrical costs are pretty low in Florida (or where) so electric might be a good choice for operating costs. The heat pump will be the most capital cost but will be the cheapest to operate over time.
 
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Old 02-27-14, 04:54 PM
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Ultimately, a Electric Heat pump would be the best option. They use these in refrigerators to cool, are extremely efficient and can heat water too. Would use an electric water heater 80 gallon or more as a buffer tank (Not hooked up). With any Radiant floor system, flow is everything. Slower the better for heat transfer to slab. If set up properly, should have a manifold to regulate water flow or use an adjustable speed circulator pump. Cost is a bit cheaper to buy the circ pump. The ground water temperature in FL should be around 70-75 degrees in winter so heating water is a snap to about 100 degrees.
If it was me, I'd go Geothermal Heat Pump/Radiant floor system. It cost's 3 times as much, yet 1/3 comes back as FED tax credit and uses 1/3 the power to run and lasts 3-4 times as long as conventional heating system.
 
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Old 02-27-14, 05:29 PM
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"Would use an electric water heater 80 gallon or more as a buffer tank (Not hooked up). With any Radiant floor system, flow is everything. Slower the better for heat transfer to slab."
This is not actually true.
We try to run a 10 degree delta t across radiant slabs to even out surface temps.
Low flow = low BTU output.
Low flow = warm at the supply and cool at the return.
This is quite the opposite to what we actually want in a radiant system.
I agree, Flow is everything but it has to be designed correctly.

If I where in FL, I would not spend the capital cost to install a small geo (ground loop) system, not for a 1000 sq.ft slab that maybe needs 10,000 btu to heat the space. I would however use a air to water. Even at the coldest FL will ever see these units should be 300% efficient.
 

Last edited by NJT; 02-27-14 at 06:16 PM.
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Old 02-27-14, 06:16 PM
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Slower the better for heat transfer to slab.
Yeah, not true... by the time the water gets to the end of the loop it has cooled enough to not transfer much heat.

Faster flow means higher AVERAGE temperature across the length of the loop, means MORE heat into the slab, and vice versa for low flow.
 
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