We just finished installing a radiant floor heating system as part of a complete kitchen remodeling in a beautiful old home walking distance from downtown Canandaigua.
Because the kitchen was stripped to the subfloor in preparation for a new hardwood or tile surface, the obvious choice was to lay the hydronic tubing on top of the subfloor for more efficient heat transmission to the living space, not to mention stapling up the tubing beneath the subfloor and between the joists would have been very labor intensive, as the room rested on a rather shallow crawlspace. We chose to encase the tubing in a thin pour of gypsum cement to accommodate the significant unevenness of the subfloor and help to spread the heat evenly across the floor.
We were initially concerned that, with all the floor cabinetry that would be installed, there might not be enough open floor space on which to install tubing to provide sufficient heat to keep the room comfortable on the coldest winter nights; adding to this concern was the fact that more than 80% of the walls in the kitchen were exterior with a moderate amount of windows and a couple of doors which would tend to increase the thermal losses. After some careful thermal modeling of the room, we concluded that, if we supplied the tubing circuits with 133F water to achieve floor surface temperatures of approximately 88F (which coincidentally is nearly ideal from a comfort standpoint), the system could handle the design load outdoor temperature of 2F. A gas fireplace was already planned for one of the exterior wall corners, so there would be backup heat for the occasional times outdoor temperatures dipped below design load. At those floor surface temperatures, hardwood was ruled out as a finished floor covering as it is generally prone to warping and separating at temperatures above 80F.
Laying tubing on the subfloor also provided us the design flexibility to concentrate the initial portion of each of the two tubing circuits along the exterior walls and especially in front of the doors and windows so that the warmest floor temperatures would be adjacent to the areas of greatest heat loss from the room.
For a small job like this – only 400 square feet – it was not cost effective to bring in a large mixer/dispenser which could accomplish a continuous pour of cement. Instead, we opted to bucket-mix nearly one hundred 50-lb bags of cement with a handheld mechanical mixer which made it imperative to have a streamlined process of mix-transport-pour so that the first bucket of cement was not set before the last bucket was poured, else we would defeat the self leveling feature of gypsum cement. Admittedly, it was a little tricky and some post-pour grinding was necessary to prepare the surface for the tile installers.
Once the floor tubing was laid and covered, the rest of the kitchen remodel could continue while we connected the circuits to the existing boiler. As the remainder of the house was heated by baseboard and old-fashioned radiators, the boiler water temperature was much too high for the radiant flooring system. To address this, we installed a mechanical mixing valve with a downstream thermometer which would blend fresh hot water from the boiler at approximately 160oF with cooler water returning from the floor circuits at approximately 120F (and adjust it) to achieve our 133F target. Just downstream of the mixing valve, we installed a quiet Taco circulating pump which is controlled by a Leviton thermostat that accommodates a remote temperature sensor. The thermostat was installed out of sight in the kitchen closet and the sensor was invisibly mounted flush into the drywall in the center of the room adjacent to the cooking island but facing away from it so as not to be influenced by the heat radiating from the stove top.
We’re looking forward to checking in with the clients next winter to see how they’re enjoying their new radiantly-floor-heated kitchen!
