retro fit under floor heating

Under floor heating "staple-up"

Yes, even with existing hard-wood, you can have radiant floor heating!  There are a great deal of misconceptions around radiant floor heating and, in particular “staple-up”.   The comfort of under-floor heating can be retro-fitted to existing floors, the process is often referred to as Staple-up as the tubing or, more often, the insulation is attached with staples.   It is a very effective way to get the comfort and efficiency of a radiant heating system into an older home.

I once had a customer complain that he had a problem with his staple-up system, “When my in-laws visit, they take off there shoes and socks to enjoy the warm floor, I hate looking at their feet!!”.



Loops of PEX tubing are attached to the underside of the  sub-floor, one loop in each bay.  Approximately 1″ below that an aluminum foil faced insulation of R19 or greater is attached with the foil closest to the tubing.  The one inch gap allows for an air circulation convection current around the tubing which spreads the heat evenly across the joist bay.  The aluminum foil of the insulation reflects the infra-red heat upwards, through the floor to warm the space.  This does warm the floor, however, the requirement is to warm the space.  The comfort and efficiency of radiant floors are well known, please read “comfort from the ground up

foil stapled to underside of floor

Foil attached with staples

It is very important that this system is installed correctly.  Incorrect water temperature can lead to buckling of floors, improper materials or installation practice can lead to noise.

Hard-wood floors are pretty tough.  The sun shining in through a window can heat up a floor to considerably higher temperatures than any heating system should create.  Operating temperatures of staple-up systems should not exceed 150 degrees F with floor temperatures of around 75 to 80F max.  Again, the system is designed to heat the space, the warm floor is a satisfying by-product.

Heat transfer plates are one method of installing retro-fit heating.  I used to use this method, we found that if we used the wrong type of PEX tubing, the plates would pinch the tubing and there was a creaking sound when the system was heating up and cooling down.   We switched to using non-barrier PEX with climbers chalk in the aluminum heat transfer plate to allow the pipe to move.  Heat transfer plates are effective,  they are very efficient for heating the space, however the installation is costly and they are less effective at transferring the heat evenly across the floor.  There can be hot spots.

Radiant Foil insulation, such as TVM, has incredible insulation qualities and works extremely well with this system.  It may be more expensive but it is very effective and easy to install.

Tubing attached to the sub floor with foil faced R19 insulation is probably the most cost effective way to have clean, silent, energy efficient and luxurious radiant floor heating in an older home.  It can be installed in new construction and additions too.  We often incorporate staple-up into  other parts of a heating system,  for example:  with a basement conversion we might put tubing in a new concrete slab and then use staple-up in the joist bays of the floor above.

Talk to an experienced installation contractor about staple-up and be sure to check references.

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