Proper operating temperatures for radiant heating systems.

This article discusses the maximum, minimum, & recommended operating temperatures for radiant heated floor systems, including typical temperatures used in different types of radiant-heated floors: tile, wood, laminate, carpeting, etc.

We describe the normal or correct radiant heat setting temperatures and we explain what happens if the radiant heat temperatures are set too low or too high.

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What are the Normal Operating Temperatures for Radiant Heat Systems?

Our page top photo shows the output temperature of an electric boiler used to heat tubing in a radiant-heated tile floor set over concrete in a Minnesota home. Unfortunately that system never worked satisfactorily, as we explain
at RADIANT HEAT FLOOR MISTAKES.

Question: what is "normal" and what is "too hot" for radiant heat water circulating in the piping?

I just inspected a complex combine forced air (hydronic) heating system combined with a several circulating radiant floor heating components. My question is what is normal and what is “too hot” for the water circulating through the piping distribution under ceramic tile floors installed over wood framed floor systems.

When I took the Watts® Regulator course they emphasized that temperatures should not exceed 130 degrees. During my inspection the water leaving the boiler was 167.8 degrees (going into the heating distribution system for hydronic radiant, hydronic forced and also potable (yeah, I know that part is a problem!). - Ron Wells (ASHI#515) Wells Inspection Services, Inc.

Reply: It depends ..

The high temperature effects of too-hot radiant heat under wood flooring, and the effect on finished wood flooring are cited
at WOOD FLOOR DAMAGE, and
some radiant heat design specs are
at RADIANT HEAT FLOOR MISTAKES.

Here we add details about different operating temperatures for radiant heating systems.

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. The control on that boiler's circuit board is shown just above.

But as we explain below, the optimum operating temperature for radiant heat floor systems will vary depending on the insulating or heat-conducting properties of the flooring material itself.

Typical Temperatures at the Upper Surface of Radiant-Heated Floors

Unless you have a black crayon and an infrared thermometer it may be a bit more difficult to measure the finished-floor surface temperature (what your bare feet would feel when walking on the floor) than it is to just look at a temperature gauge on the hot water heating pipes or heating boiler themselves, but looking at the finished floor surface is one important temperature to note.

The finished floor surface temperature is what the building occupants feel when walking on the floor, affects the rate of heat radiating into the air above the floor, and if too high, can also become a safety concern.

According to CMHC (Canadian Mortgage and Housing Corporation) the finished floor temperature should never exceed 85 F (29 C).

Our photo (above) shows our friend Steve and his dog explaining the radiant heat tubing layout in the new garage floor slab of a Minneapolis MN home.

Watch out: Note that for special installations such as a driveway de-icing installation the radiant heat system operating temperatures will be higher than used in an in-building heating system. Be sure that the tubing you select is rated for use at that operating temperature.

Our photo (left) shows an abandoned driveway de-icing radiant heat system that has been abandoned. Only the mainfold remains in place near the home's heating boler.

Watch out: if you saw 167.8 F at the boiler, that sounds too hot for normal circumstances on a radiant heating system. Running a radiant heat system hotter than necessary can have a range of harmful effects including:

• Shorter heating boiler life
• Shorter radiant heat tubing life
• Oxygen diffusion problems [discussed below]
• Uncomfortably hot or even dangerously hot floor surfaces
• Unnecessarily high heating system operation costs

See PEX PIPING INFORMATION for more details about temperature ratings of plastic tubing. It may be useful to ask why someone has set the temperature of this radiant heating system so high. It could be

• Simply a mistake
• A control not functioning properly
• An improperly installed or designed radiant heat system that is not delivering adequate heat into the occupied space
• A misunderstanding of the controls or a misread of the temperature at the wrong location. See "Where to Check the Temperature ..." at the end of this article.

Typical Radiant Heat Temperatures Under Ceramic Tile

Under ceramic tile a higher temperature might be allowed without risking floor damage (we don't have wood shrinkage for example) and/or might have been set by a homeowner who likes a really warm bathroom floor. But since ceramic tile is a *better* heat conductor than wood flooring, if anything, one would expect the temperature setting for that floor to be lower, not higher than otherwise.

Radiant under ceramic tile or vinyl tile, lower end of the temp;

Typical Radiant Heat Temperatures Under Finished Wood Flooring

Under wood floors nailed right to the subfloor and tubing below, radiant heat temperatures are typically at the middle of our 85-135 °F. temperature range, or about 105-115 °F.

The radiant heated wood floor shown in our photo (left) was installed in a New York home.

Attempting to "drive out" tubing odors the installer pushed the floor temperature up a bit too high, taking the blame for gaps that appeared in the flooring as a result discussed at at WOOD FLOOR DAMAGE.

Radiant Heat Temperatures Under Laminate Flooring

Under laminate type finish flooring, keep the temperature under 82 °F or risk floor damage (per http://www.shawfloors.com/)

Radiant Heat Floor Temperatures Under Carpeting

Under carpet over subfloor, radiant heat will need to operate at the higher end of its temperature range to overcome the insulating effect of the carpeting and carpet padding.

Oxygen Diffusion in Too-Hot Radiant Heated Floors

Radiant Floor Company, a radiant heating system manufacturer, raises another interesting point, indirectly: at temperatures over 140 °F can cause an oxygen diffusion problem and require special "oxygen barrier" tubing in some cases (depending on the boiler design) - otherwise system life may be reduced or the boiler damaged.

Where to Check the Temperature of A Radiant Heated Floor System - Mixed Radiant & Hydronic Baseboard or Radiator Heating Systems

Watch out: often there are mixing and flow controls on the radiant system that limit the actual temperature in the radiant tubing, typically by only introducing new hot water into the loop when temperature requires it - otherwise recirculating most of the loop water without returning it to the boiler.

You will particularly see this if the boiler is serving a mixed-design system, including some heating baseboards and other radiant floor heated sections.

That's because we want the hotter temperatures in the baseboards (hotter is more efficient heat transfer), and cooler temps in the radiant flooring.

So: was this a mixed design system with some baseboards and some radiant? and were there mixing controls on the radiant loop section ?

...

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