Radiant floor heating made good sense after we found 60 degree well water in our yard.
We thought Radiant floor heating was one of our heating options when we starting planning our home. When the well driller discovered 60 degree well water we decided to definitely adopt radiant floor heating.
We also determined early in the planning process that we wanted a single story home without stairs. Stairs cause most home accidents, especially for the aging population. Thus people can assume retiring baby boomers will be buyers of one-level homes like ours. A one level concrete slab over grade also provides the best medium for a radiant floor heating system. A concrete radiant floor also stores huge amounts of passive solar energy to assist any active solar heating system.
Radiant floor cooling never crossed our minds until after our house had been finished and occupied.
We experienced some very warm summer weather after moving into our home. Never did we expect the solar gain to be so much in the summer because of the low E windows. However, indirect lighting can apparently heat the house in the summer with so many south facing and a few west facing windows. I thought our super insulation would protect us from the summer heat much like adobe buildings in the SW stay cool. They apparently don’t have any windows though and that makes a big difference.
I knew that standard air conditioning was out of the question because we had no room for the duct work or an air handler. The radiant floor “experts” warned us of condensation and mold problems if we tried to cool our floors. But I knew that our relative humidity was very low all year. A few studies on hot and “humid” (for us) days proved me to be correct.
We found our cooling solution for NO extra capital cost!
With nothing to lose I simply reversed the heat pump from heating to cooling mode by changing a wire jumper. I also had to reprogram the aquatstat that controls the buffer tank water temperature range. In the summer we cause the heat pump to take heat out of the buffer tank and deposit it into the well water. The discharged well water might be 72F instead of the original 60 degree temperature.
The water coming out of the buffer tank is seldom below 60 degrees because we maintain the floors no colder than about 68. Neither temperature is ever at risk of falling below the dew point all summer so I don’t even bother checking any longer. But I offer a word of caution. This floor cooling technique has many advantages for owners of radiant floor heating systems. HOWEVER, most areas of the country have too high relative humidity levels in the summer for this technique to work. If you are tempted, be sure to consult with an appropriate thermodynamics or HVAC engineer to advise you.
We have had great experience with the radiant floor cooling. However, we found another way to stay cool in the summer while using even less energy. I explain all about this new cooling application we have adopted here.
The first construction phase for radiant floor conditioning is the frost wall cement foundation.
The radiant floor professionals convinced us that we should install a four foot frost wall around the perimeter of the slab. The wall would block winter frost from penetrating under the floor. The builders covered the entire outside surface of the frost wall foundation with a tar vapor barrier before they added two inches of R-10 GeoFoam insulating board.
Insulated Frost Wall Over Compacted Engineered Fill Makes the Radiant Floor Heating an Easier Job
A radiant floor heating system presented more complexity than we expected.
For starts, someone had to apply a number of different materials in layers, over the leveled and compacted gravel base discussed above. The workers applied the materials in the following order from bottom to top:
- Vapor barrier
- GeoFoam insulating board
- Six inch square grid steel concrete reinforcement mesh
- Rehau Pex tubing attached to the steel mesh
- Concrete poured slab
- Finished flooring (stain, special vinyl, tile, radiant floor carpeting, wood, faux wood, etc.)
Place items 1 and 2 first; the vapor barrier and GeoFoam boards.
Each of these materials will cover a total area of 5200 square feet, all under one roof. Workers first covered the entire 5200 square feet of slab area with gravel they leveled and compacted. The owners laid a plastic moisture barrier over the gravel along with six inches of GeoFoam board over the vapor barrier in the house portion of the slab. That board yields R30 insulation value under the house concrete slab which really reduces heat loss into the 45 degree ground.
The garage typically is only heated to 55 or 60 F in the winter, thus the owners installed just two inches of foam board (R 10) over that floor. The lowered shop air temperature reduces heat losses thanks to the small temperature gradient between the floor and the ground. Hence, less insulation value is not necessary to maintain low heat losses into the ground.
Less shop floor insulation might provide another nice advantage in extremely cold winters with temperatures falling below 25F. The 45 degree earth acts as a heat sink or a heat source depending upon the direction of heat transfer. Instead of cooling the building, the earth can at times also help maintain enough heat to keep the floor from freezing. Otherwise, the shop might cool below freezing if insulation was too great and outside temperatures were minus 30 degrees. By the way, the house requires higher average temperatures than the shop and therefore the R10 insulation simply would not be enough in living quarters.
One big wind storm really delayed the radiant floor heating schedule!
It was a Montana”Micro Burst” that slammed us with wind gusts greater than 80 mph on that fateful September day. Those short-duration winds carried away most of the foam board we already had covering the sub floor gravel at the time. The southerly gusts did all its damage within minutes, even though we weighted the foam down with loads of 20 foot 2 X 4’s and five foot steel “T” fence posts. The micro burst only spared one section of foam because it was nestled against and below the top of the south frost wall.
The picture below (left) shows the only portion of the building to escape the big wind storm. Wind gusts lifted most of the vapor barrier and foam boards off the gravel like a big dangerous kite. Finally, the material fell back onto the ground, thereby littering the northern landscape for up to a half mile or so. Several truckloads hauled the material off to a landfill.
Next you will install items 3 and 4; the six inch reinforcement steel mesh and hydronic radiant floor heating tubing.
After the workers laid out the six inch steel reinforcement mesh over all the GeoFoam insulation, the tubing installers wired the hydronic tubing to the wire mesh (first picture). The lower picture shows the radiant floor tubing all installed and ready for the concrete pour.
Item 5; Concrete applicators poured and finished the final floor just before the first seasonal freeze.
The concrete capped off a series of operations labeled 1 through 4 above.
Unexpected Freezing weather can spell disaster for a concrete pour. The concrete people left the job with long-held elk hunting plans thereby leaving the owners to deal with the unexpected freeze. The owners rented concrete insulating blankets and spread them over the concrete. Automotive headlights lit up the area enough to finish the job in total darkness. All this happened while another wind front passed through. What at job!
Temperatures dropped into the low 20’s that night. All our hard work saved us from having any concrete damage so it was worth our torturous efforts.
Item 6; Much later, the owners stained and sealed the concrete in the house.
Initially the owners stained and sealed the house floors as a temporary measure. A larger solar system (installed in 2016) now makes it feasible to use wall to wall carpeting in major parts of the home. Other parts of the home might be accepting floor tile in the future.
Thank you for staying awake (or did you?) for this presentation!
The next section discusses outside insulated walls. Part of the new concrete slab discussed above supports the first of the Structural Insulated Panels being installed. I took some nice pictures of the entire concrete pour that showed no other distractions. Sadly, I have been unable to find them. I sincerely hope you will find the next section to be informative and that the content will be inspiring for your own projects projects or an entire building project.