Radiant Floor Heating Above or sub-floor radiant heating, geothermal radiant floor solutions,

Radiant Floor Heating Above or sub-floor radiant heating, geothermal radiant floor solutions,

Radiant Floor Heating /Above or sub-floor radiant heating?


We’re beginning to build a two level mountain home, 4600 sq ft on main level

with a full walkout basement. We plan to install hydronic radiant heat in the

basement, in the stained concrete flooring. My question is which installation

would be better for the main/upper level? We plan to have hardwood

flooring in most rooms on the upper floor, tile in the bathrooms and one TV

room will have carpet. I have one installer that says to install the PEX under

the sub floor, the other installer says to lay the PEX on top with a layer of thin

set concrete. Which is the better application with the hardwood floors?


I use staple-up or “sub-floor” hydronic heating systems most often in retrofit applications and they work great at creating comfort. Sub-floor systems are usually less expensive to install — requiring less material AND labor but will cost more to operate because of the higher water temperatures required to overcome the R value of the typical sub-floor which must be added to the R value of the finished floor. The designer must take extra care in his heat load analysis as the output of sub-floor systems can be quite low and may fail to satisfy the heat load in a given structure.

I own a 100-year-old home with a sub-floor system driven by a conventional cast iron boiler operating at 180°F. However, it is not what I usually recommend for new homes.

I prefer to design systems using the lowest design water temperature (the temperature heat transfer water will reach on the coldest day of the year) possible. This is especially true if you are considering a very GREEN Mod/Con boiler or geothermal heat source.

With this in mind and considering the added resistance floor coverings like wood and carpet can present, I would lean toward above floor or «sandwich» radiant floors such as Twin-Track by Uponor, SubRay by Watts Radiant, Rehau’s Raupanel or Viega’s Climate panel system.

Tubing sandwiched between sub-floor and finished floor are quite responsive with material costs still quite high and labor moderate depending on the manufacturer. These systems have a reputation for making noise – ticking or snapping — so be careful to ask your contractor about this potential problem. Some of the manufacturers do a better job addressing this issue than others so it is up to the installer to research the product and apply the technology properly.

The other option is a «wet» system also applied above the sub-floor whereby tubing is typically stapled or snapped into tracks and covered with concrete or lightweight gypsum based underlayments. I like both systems for their response time and the fact that they are almost always absolutely silent in operation.

Wet systems use gypsum or concrete and are my personal favorites — and one of the first systems I ever designed and installed — giving the talented designer great flexibility. Again, material cost are high but labor costs for the hydronic installer are dramatically reduced, water temperatures are as low as possible and the homeowner gains the added benefit of fire rating, sound control between floors and thermal mass, meaning the floors will typically feel warmer longer than other applications. This is a factor of design strategy that can be applied to all floors but is built in to higher mass wet floors.

The final consideration is floor coverings. Wood and carpet resist heat, so design temperatures are critical and can effect response time. Improper application can lead to annoying and unnecessary lead and lag in the heating systems; meaning a room may be hot or cold depending on the weather swings: something that does not happen in a properly designed radiant floor heating system.

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