My radiant floor

777 · December 2010

I've had it in for three years now and I'm very happy. I didn't do load calcs. etc but it's performance seems excellent. It is staple up with mostly the thin aluminum transfer plates, and some extruded aluminum plates along with R-13 insulation below. I was a little worried because the floors vary in thickness, some areas have 3/4" pine subfloor with 5/8" or 3/4" maple hardwoods other areas have 3/4" pine sub floor with 3/4" plywood with ceramic tile on top of that. I could only do the first floor of the house, but I did add some in the upstairs bathroom using Roth towel warmers. The towel warmers work like low temp emitters rather than actual towel warmers, but the bathroom is comfy warm. The towel warmers only get between 90 and 99 degree F temp water depending on reset temperature which dries the towels nicely, adds heat to the bathroom.

I don't do floor sensors, but rather use one vision pro ambient temperature sensing thermostat. I keep the temperature at 68 continually. I use a perless pinnacle 60K but modulating condensing boiler, it doesn't short cycle and always runs at its lowest BTU output. Like I said earlier my water temperature runs between 90 and 99 degrees F. in a cold wisconsin climate that seems pretty good. My delta is only 10 degrees but I figure it probably keeps the heating pretty even. My boiler has quite long run cycles which I think is desirable, but sometimes I wonder if it wouldn't be better to raise the temperature a bit and reduce the run cycles. I mean the boiler is supposedly 94% efficient, but if it runs for a long period of time that is 6% loss out the PVC "flue". If I shorten the fun time with slightly higher water temp. my run efficiency drops slightly, but my run time decreases...so what's better?

So the heated area of the house is about 1300 sq. ft (A portion of the upstairs is heated with a 9000 BTU Samsung minisplit heat pump) and my natural gas bills never exceed, $110 and that includes NG domestic water heater. I know it's relative to gas bill rates, but you get some idea. I will say my house is insulated quite well--the upstairs all foam and the downstairs blown in cellulose.

The bottom line here is that I wouldn't necessarily recommend using my method of installation with no heat load calcs., but staple up floor heat worked good for me, and most information read I would need much higher water temperatures to heat my house aren't accurate; at least in my case. With 68 degree F thermostat setting my floors only get to about 70 degrees F as revealed by my infrared thermometer...not exactly toasty, but still quite nice. Additionally some sites say never exceed 80 degrees F. for floor temp. well If I got anywhere near that temperature my house would be a literal oven. I will say the maple floors gaps to enlarge in the heating season, but that is a small tradeoff.

furthur · December 2010

my cold climate staple up...

My experience with my little pilot retrofit project is similar. I've recently, in this cold spell, been turning DOWN the water temp...getting return temps below 100 deg. with thin plate staple up, ambient temps approaching 0 deg F (Anchorage, Alaska). I'm starting to wonder if I still need to mix down the pex-in-slab zones...we'll see when I start up the first two rooms in a few weeks.

Only problem with lower water temps is that noisy pump running more. It must be something with the plumbing, even though the suction is more than 12D, and the check is far enough downstream (maybe I should try closing down the Wirsbo manifold balance valves?).

Gonna try the Grundfos Alpha, with a Webstone check/flange for the low temp, running Wirsbo motorized zone valves, and micro-zoning each bedroom. This is for thin-slab (2" concrete) over 2" foam over existing uninsulated below ground slab.

Not that it's been easy, learning the hard way. So much dis-information out there.

John

NRT_Rob · December 2010

a few things to both of you.

1. If your floor surface is 70 in a 68 degree room, that's about 4 BTUs/sq ft. that's a truly tiny heat load. any method would work fine with a load like that. But I suspect your reading is not accurate, or it was taken when it wasn't very cold or you had other heat gains going on.

2. You want mod boilers to run constantly if possible. Cycling is the worst thing for it.

3. Real load calcs by a pro would have answered all these questions and frankly, if your loads are this low, you didn't need plates at all. Radiant ceiling might have been a better option as well, though plateless floor radiant is pretty cheap, radiant ceiling is a close second. It's definitely an easier install in most cases.

4. microzoning will induce cycling issues and should only be done with electronic intelligence to combat it, or a buffer tank, on a mod/con boiler.

5. floor issues are likely related to installation moisture content of the wood. At these temps you're barely operating them higher than a regular room temp even on the radiant pipe side.

My radiant floor

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