Floor temperature range for radiant heat

rockwaterMarch 19, 2010

What is the maximum floor temp for real wood flooring?

What is the average water temperature through the tubing?

Thanks

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kudzu9

For my system, which is in a concrete slab with no other flooring material, other than carpeting in a few rooms, the boiler setting for the water temperature is at about 115F. I don't know if this setting varies significantly depending on the climate/boiler/tubing/flooring material, etc.

    Bookmark   March 21, 2010 at 2:00PM
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brickeyee

A 115 F floor would be so hot you would not want to walk on it barefoot.

This is one of the limits on radiant floor heating.

If the floor is required to be much over 80n F the design will not work well.

The boiler temperature is rarely the actual circulating temperature, and if you boiler is only running at 115F it is not going to have a long life unless it is a high end unit with a stainless steel heat exchanger.

A cast iron boiler needs to be much hotter than 115 F to not rust and corrode from the outside in.
At 115 F the flue gases will be condensing on the boiler heat exchanger and corroding it very badly.

A tempering valve is often used to allow the boiler to run at a high enough temperature for long life, while mixing returning water from the floor into the hotter water from the boiler to keep the floor temperature down.

    Bookmark   March 21, 2010 at 7:42PM
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kudzu9

The thermostat is set to 67F during the heating season, and the floor is comfortable, but not overly warm. With radiant heating installed in concrete floor slabs you're obviously dealing with a large thermal mass, so you need a decent temperature differential to have decent heating response, hence, the 115F boiler setting. The boiler system is 9 years old, I'm following the manufacturer's recommendations for the temperature setting, and I've never had a problem with it. Also, it's the most comfortable and stable heat I've ever had in a house. Finally, having the floor slightly warm allows us to set a lower ambient temperature in the house and still be comfortable. Works for me...that's all I can say.

    Bookmark   March 22, 2010 at 3:03AM
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deirdrelouisville

I have boiler fed radiant heat under wood floors and in a new cementer kitchen floor. Under the wood floor, we often run the water at 125-130 degrees-- Of course, the surface of the wood is nowhere near that hot- the tubes are suspended below the flooring.

    Bookmark   April 10, 2010 at 6:43PM
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brickeyee

"... boiler fed radiant heat under wood floors and in a new cementer kitchen floor. Under the wood floor, we often run the water at 125-130 degrees..."

You should have a tempering valve installed on the output of the boiler that mixes some of the returning water with the boiler output to lower the water temperature.

Boilers have very short lives if they do not heat up enough to cook off the water vapor created from the burning fuel.

Hot water heaters are even sometimes used to feed radiant underfloor heat. They are more tolerant of the lower temperature operation since hot water is rarely above 140 F in a home heater.

    Bookmark   April 13, 2010 at 4:16PM
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doubler

I have radiant heat in my kitchen. I didn't install it, was here when we bought the house, so I don't know everything about it. Was told by previous owner that the tubing is in concrete. It was done in 2000. Under the kitchen is a full height basement that is not internally connected to the main basement of the house, hence it is very cold. There is a full height door to the basement under the kitchen that does not seal well. The ceiling of the basement is insulated. In extreme cold our kitchen will only heat to about 64. Should/can I turn up the temperature of the water going through the floor when it is extremely cold? I am in eastern PA and the last few days we've had lows in the negatives and highes in the upper single digits to low teens. Thanks!

    Bookmark   January 24, 2013 at 7:47PM
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liriodendron

I have lived with hydronic radiant heating under oak T&G over a concrete slab. It is a wonderful heating method.

However it is not a quick response system so I question whether raising the temp of the boiler will result in an increase in room heat over the next few days, or in enough time to cover the next few days of frigid weather. (I am much north of you in the upper Hudson Valley so I'm having the cold snap as you, only colder.)

If you have a tile floor over the radiant heat it may not hurt to try turning it up (though your fuel costs may be significant). But if you have wood over the radiant heat, I'd be leery of raising too much, too quickly or at all. Wood does work over radiant, but it isn't the easiest and best top surface. You could see some separation between the boards promoted by the higher temps and lower humidity.

I'd try warm slippers and a sweater for the next few days and just consider it one of the small, occcasional, prices of having an otherwise extremely efficient highly livable heating system.

HTH

L.

    Bookmark   January 24, 2013 at 8:50PM
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kudzu9

doubler-
Have your system inspected by a firm that specializes in your type of heating system. I have a radiant heat system installed in my concrete slab floor. About a year ago I had one part of the house that was not getting up to temperature. The house is zoned with 4 separate heating manifolds and the thermostatic switch in one of the zones had failed. Once the failed switch was replaced, things went back to normal. Good luck.

    Bookmark   January 27, 2013 at 4:11PM
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jpm1953

I know these are old posts, but I live in Maine and have worked on heating systems since 1980. Up here we install a mixing valve because we also run other zones. It allows you to run your boiler at a high temperature.

    Bookmark   April 24, 2014 at 4:08AM
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Mayaa

yes i think 115 F is too hot and may not be appropriate ....

    Bookmark   April 25, 2014 at 10:33AM
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jackfre

Boiler output temp supplying the floor will depend upon which type of system you install. If it is to be a"staple-up" you will run as high as 130-140. The tubing is not directly in contact with the floor in this set-up. It is installed a couple inches below the sub-floor and there are aluminum or sheet emtal transfer plates below the tubing. That is all insulated to keep the heat against the floor. If you had a Warmboard type install above the sub-floor you would run much lower boiler temps and have better response. As noted previously these "thru the wood" systems work well but you will not heat the place up quickly.

    Bookmark   May 6, 2014 at 8:55PM
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