Sunday, December 28, 2008

10: Radiant Heat

Radiant heat systems are really easy to install during construction, and if there's crawl space under an existing house, the system can still be installed without too much trouble. Getting it under the second floor of an existing house would be a different issue, but the installation downstairs and upstairs went quickly in my house—maybe a couple of days for the whole system. I'm utilizing a closed loop hydronic system which means that water is heated and pushed through a network of plastic tubes stapled to the sub-floors of the house. Basically, there are two runs of the tube between each floor beam, and they're covered with a sheet of something that looks like metallic bubble wrap to push the heat up into the floor and house. My system is very basic with one zone for the first floor and a second for the upstairs.

There were a few things that I did learn about radiant heat:

- It works under most surfaces, but it never really makes stone surfaces feel warm. They just feel neutral, which is not bad at all. Upstairs I used engineered wood planks, which do feel a little warm to the touch, especially if something has been covering the surface for a period of time. But, no surface is ever hot.
- The rooms heated by the system feel pleasantly neutral in temperature. I keep my thermostats set at 69 degrees. As I understand the principle, warmth under foot makes you feel warmer than heat blowing around or radiating from above. I find that if the system is set at anything higher it can feel uncomfortably warm–but I guess that's very subjective.
- When I'm away for more than a day or two, I'll lower the thermostats to 55 degrees to conserve energy. It does, though, take six or more hours to bring the house back up to 69 degrees when I return. Radiant heat systems are not meant to change interior temperatures quickly. Think of them as slow, steady, efficient heat.
- It's a blessedly quiet system to operate and the interior air doesn't dry out from forced hot air, which is the worst in my opinion.
- My closed loop system is filled with plain water. Sometimes people will add a little anti-freeze fluid that can be purchased for a system, but with the insulation in my house, I'm not worried about any potential freeze situations.

1 comment:

James said...

That's exactly like my system that I installed 8 years ago, when I built my house. The shinny bubble wrap stuff is Refletex.

I also super insulated my house, R35 walls, triple pane argon filled Low-E windows, & R65 ceilings.

I set my high efficiency boiler to 140* in winter & 120* in summer. It also provides DHW to house.

In winter, water exits my boilers heat exchanger at about 130* & returns at about 115-120* from the 3 zones.

My 3 cheep mercury air thermostats control 68* room temps. with no noticeable over or undershoot.

My tile floors run about 70* when it's 32* outside & about 72* when it's 0* outside. They never feel warm to a naked foot. I think this is due to how well the house is insulated. If I had less insulation then the floors would have to run hotter.

I live at 8,500' elevation so my 90KBTU (input) at sea level boiler puts out about 50KBTU (why do the call this MBH ?)

At -20*F outside, it runs at about 25% duty cycle, off 75% of time.

James W Patrick