Details Hot Water Under Floor Heating??

[GT2]

Just curious, Is there a way to use a gas instant water heater with these systems? Would it be more efficient than a boiler or hot water tank?

 

[ktm250rider]

Just curious, Is there a way to use a gas instant water heater with these systems? Would it be more efficient than a boiler or hot water tank?

Yes, check out AIMradiantheating.com. My buddy used their system in his house. He said it worked great for the short time he was able to use it. He got divorced and they sold the house before officially moving in.

 

[kmdigital]

There are several points to keep in mind.

First, the key to heating a bare floor is to make the temperature as even as possible, otherwise you will have noticable cool spots in the floor. You will probably have that somewhat anyway where the joists are, but you want to aleviate that as much as possible. Because of this, I wouldn't recommend the aluminum plates. They don't do that good of a job of distributing the heat, and the floor will be very noticably warmer directly above the pipes, and cooler the farther you away you get.

Because of this, you would be better off either looping pex pipe on the sides of the joists (NOT against the subfloor) and insulating below as much as possible. A good product to use is R-Board insulation with foil on the one side. Put the foil up to provide a radiant barrier and to reflect the infrared rays upwards to warm the subfloor. You can also use fin tube as suggested, and it will work just fine.

Second, you will probably need about 150-180 degree water to make the floor nice and warm on bare feet, so a mixing valve may not be required. Obviously, if you use pex, and your water gets to 220 you are exceeding the operational limits of the pipe, so the fin tube and copper pipe might be a better option.

The other thing is, does your boiler need to get that hot to heat your house? Most baseboard heating systems are sized to provide the required heat output using 180 water temps. Usually, outdoor reset controls are porgrammed to provide water temps between 140 and 190 degrees depending on how cold it is outside. If you can limit it to something under 200 degrees pex pipe would be the easiest and quickest to install, and could be used without a mixing valve of any sort.

 

[NY_Yankees_Fan]

KM,

I like your idea on using standard hot water baseboard fins. I will install a ball valve to limit the flow to somewhat control the heat. I think this would be the cheap way to go. The mixing valve and manifold for such a small system would be a lot more.

Thanks for all that make comments.

Now all we have to do is pick out the kitchen cabinets.

 

[quicksandfarmer]

I will install a ball valve to limit the flow to somewhat control the heat. I think this would be the cheap way to go. The mixing valve and manifold for such a small system would be a lot more.

From the been-there-done-that files: it is very hard to control the output of a radiator with a simple ball valve. The problem is that the heat output is extremely non-linear to flow. For example, if you have a radiator rated at 10,000 BTU/hr, at its rated output the water flow is 1.04 gallons per minute. If you want to throttle that down to 7500 BTU/hr, you have to drop the flow to 0.22 gallons per minute, and at 5000 BTU/hr the flow drops to 0.09 gallons per minute. It's really hard to crank the flow down like that with any accuracy, and a ball valve is a pretty blunt instrument. (It works the other way too -- once you reach rated output, doubling the flow only increases the output by about 5%).

That's why the conventional way of adjusting heat output is to control the water temperature. You get much better control.

Since it's your house, you have the luxury of being able to fiddle with it until it works. I would install it, run it off straight boiler water, and see how it works. If it's too hot I would watch Ebay for a cheap mixing valve. Generally fittings for smaller pipe are substantially cheaper, so I would plumb it with 1/2" pipe if possible.

I also can't believe I'm helping a Yankees fan. Oh well, it's only spring training. And my advice may be wrong... Go Sox!

 

[NY_Yankees_Fan]

Quick,

Thanks for all the info, and practical advice to a fellow baseball and tractor lover.

 

[Asymtave]

Yep - I found that out the hard way. It took a lot of "taps" of the valve handle to get it just right. But then again it's my house. Hard to believe how sensitive it is, and now I know why. Thanks.