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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.
We discuss: Radiant heat temperature settings at the boiler. Radiant heat temperature settings in the tubing. Maximum temperature for radiant-heated floor surfaces. Energy efficiencies of radiant floor heating. Heat loss rates into earth below radiant heated floor slabs. Operating temperature comparisons for types of radiant heating.
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,
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
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. Radiant heat tubing was installed under the concrete floor to provide a heated garage. The open corner garage door design permitted cars to turn into the garage from a narrow alley.
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).
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 ?
Question: how can I boost the temperature of our radiant-heated floors?
I have radiant heat floor throughout my house and I have some questions about boosting its output. I’d love to enlist the serves of someone from your team who can answer questions about heat exchangers, optimal temperates, max temperatures, etc.
The sooner the better as we are feeling chilly at the moment. - Anonymous by private email 2017/12/11
Reply: (Mod) said: take care not to over-boost radiant heat floor temperatures
I may be able to answer specific questions or I may have a few suggestions but you will be best served by an on-site expert who can look at your equipment, controls, house and its design and points of heat loss.
Watch out: In general, if you boost temperature too high with a radiant heat floor you can find the floors too hot to walk on comfortably; and of course adding rugs to make walking comfortable block the heat output.
I would take care to keep your radiant heat temperatures in the heating loop under 135°F (57°C).
The finished floor temperature should never exceed 85°F (29°C).
That is typically managed by adjusting the temperature controls at the mixing valve that maintains the floor temperature by mixing in return loop water with outgoing water from the circulator/boiler.
Too much heat can also damage floors if they're wood, and too much heat may exceed the rating of the radiant tubing that was used, leading to a tubing failure - costly leaks.
My photo shows gaps that developed in a wood floor installed over radiant heat tubing after the radiant heat was driven to temperatures above those recommended by the radiant floor heat system manufacturer.
Start by finding the operating temperature of your system as it is.
Consider also looking over the home to reduce its heat loss, particularly if there are drafts.
I cannot assist on a for-pay consulting basis. We do not sell anything. In order to absolutely assure our readers that we write and report without bias we do not sell any products nor do we have any business or financial relationships that could create such conflicts of interest.
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Azel Technologies controls, temperature gauges & thermostats for radiant heating systems
UNIVERSAL DIGITAL TEMPERATURE GAUGE: DS-60P - Quoting: The i-Link series Zone Valve Controls simplify the field wiring and yet control up to six zone valves in a multi-zone hydronic radiant heating system. The contractor friendly Printed Circuit Board eliminates the problem caused by incorrect wiring and saves hours of installation time. There would be no more “messy” look of conventional zone valve installations.
DIGITAL NON-PROGRAMMABLE THERMOSTAT FOR HYDRONIC RADIANT FLOOR HEATING - Quyoting: D-508F digital non-programmable heat only thermostat is designed to control either ambient(air) temperature (A Mode) or floor temperature (F Mode) or a combination of ambient temperature with floor temperature limits(AF Mode). An auxiliary remote sensor is provided to measure slab temperature in order to control the floor temperature(within maximum and minimum limits in AF Mode) in hydronic radiant floor heating system. It can also be used for sensing the outdoor temperature in A Mode.
DIGITAL PROGRAMMABLE THERMOSTAT FOR HEATING/COOLING & HYDRONIC RADIANT FLOOR HEATING - Quoting: Azel Technologies introduces 500 series electronic programmable thermostat that utilizes the lastest digital technologies for residential and light commercial systems. D-500 is designed for 24 Vac single-stage heating and cooling systems. D-502F is designed to control the floor temperature in Hydronic Radiant Floor Heating Systems.
The 500 series can accurately control the temperature within one degree. Reliable permanent memory retains the programmed settings in the event of a power failure. In addition, the large, easy to read LCD display with backlit makes the thermostat easy to operate and simple to program.
SOLAR DIFFERENTIAL CONTROL: DST-932 - Quoting: The DST-932 differential temperature controller is designed for the Solar Heating Systems. The DST-932 switches on a pump in order to transfer heat from solar collector to a storage tank. The controller reads the temperatures of the storage tank (T1) and of the collector (T2), when this differential temperature (T2-T1) is higher than a set value (dt), it will switch on the pump. It is possible to limit the maximum temperature of the storage tank and also activate a freeze protection function. By switching to manual mode it allows the test of the heating system by turning the pump ON or OFF. A universal sensor P-01 or P-02(higher temperature range) is supplied with the control. This solid state temperature sensor probe can be extended up to 500 feet.
Calorique Radiant Heating Floor & Ceiling Systems, Calorique LLC, 2380 Cranberry Highway,
West Wareham, MA 02576
USA, Tel: 800 922-9276, produces thin film radiant heating panel systems used for interior building heating (ceilings or floors), snow melting, de-icing, drum and tank heaitng, agricultural uses, pet heating systems, and consumer end products. The company provides radiant floor heating systems in several designs including specifically for use below laminate flooring, carpeting, and tile floors. - Thanks to reader Jim O'Dowd for suggesting this resource.
Heatshield Panels, 27354 Valley Center Road,
Valley Center, California 92082
Nuheat Industries 3105 - 6900 Graybar Road,
Canada V6W 0A5, electric radiant heat systems for use under tile, stone, and laminate flooring, 800-778-WARM (9276) Email: email@example.com
ASHRAE 25 Heating, Refrigeration, and Air Conditioning engineering standards
ASHRAE 90.1-2004 User's Manual,
instructions for the design of commercial and high-end residential buildings "to ensure their compliance with ANSI/ASHRAE/HESNA Standard 90.1-2004 including the application of principles of effective energy conserving design..."
Passive Solar Design Handbook Volume I, the Passive Solar Handbook Introduction to Passive Solar Concepts, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v1.pdf
Passive Solar Design Handbook Volume II, the Passive Solar Handbook Comprehensive Planning Guide, in a version used by the U.S. Air Force - online version available at this link and from the USAF also at wbdg.org/ccb/AF/AFH/pshbk_v2.pdf [This is a large PDF file that can take a while to load]
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Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
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The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
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