Hot spots with hydronic radiant floor heat.

5 years ago

Several years ago, I built an addition onto my house, which includes a 14 x 24 family room. The room is heated by a separate (third) zone that I installed off of a gas fired, hot water boiler. I ran two loops through each bay beneath the floor with Hepex Plus, snapped into their extruded aluminum transfer plates. The transfer plates are screwed into a 3/4" plywood subfloor, with 3/4" oak strip flooring on top. Additionally, a layer of Reflectix is stapled up under the tubing and transfer plates, for increased efficiency. The water is regulated with a Watts inline temperature control, set at 120F. The water runs out through the system, and typically returns at 100F, depending upon the day.

So with the nuts and bolts of the system explained, I began watching one of our two cats, Lucy. She sits in the same place when that zone is calling for heat, and my wife said that it burns her feet. The rest of the floor is fine, and at 65F with radiant heat, it's quite warm. Most people complain of cold spots, but this thing is super efficient, even though I think that I should roll back the temp a bit. I don't have a floor temp sensor, just a smart wall mounted thermostat.

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Comments (5)

outpaientzero
5 years ago
Too hot. Radiant floor temperature under 3/4" wood floors shouldn't exceed 80 degrees. 120 degrees going into any radiant floor in to hot.
Bruce in Northern Virginia
5 years ago
That is correct, 120 degrees is too hot for in-floor radiant heat.

If the same heat source is used for both radiators (or domestic hot water) and in-floor heat you must have a mixing valve that brings the temps down to about 80-85 degrees for the floor. You could probably tolerate temps up to about 95-100 degrees but I think temps that high would invalidate the warranty on most flooring products.

Bruce
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David Laite
Original Author
5 years ago
last modified: 5 years ago
I have a Watts temperature mixing valve, with a temp gauge on it, I'll roll it back and see how that works. It's just one small spot that's hot, the rest of the floor is fine barefoot. I was just curious why it might be a recent issue..

From one of the radiant sites:

Typical Radiant Heat Floor System Operating Temperatures

Typical radiant floor systems operate at 85 - 125 °F water temperature entering the tubing, and put the floor surface temperature about 5 degrees above the room thermostat set temperature.

Similarly other sources such as the Oregon state energy conservation department gives the typical operating temperature range for radiant heating systems at 85-140 °F (30-60C) though we agree that 140 deg.F. is a bit higher than suggested by other sources.

A radiant heat system manufacturer, Radiant Floor Company, opines that 120 to 135 deg F is "ideal" and most sources we have found discuss typical radiant heat operating temperatures in the 115-135 degree range.

Where PEX tubing is used for radiant-heat under-floor tubing, 125 to 130 °F is typical operating temperature used for water entering the tubing.

Most radiant floor heating systems we've examined run at around 115F water temperature entering the tubing of the radiant section, and you'll see by the temperature gauge at the top of this article that 115 °F was the factory default set temperature on the control of an electric radiant heat boiler we installed.
Jake The Wonderdog
5 years ago
@Ryan Stephen

Not sure how this is related to the original post.
outpaientzero
5 years ago
Red green said if the women don't find you handsome at least let them find you handy.

I'm the handiest in town, good job Ryan and don't forget the duct tape.