If you live somewhere where it gets cold you may be familiar with the feel of cold concrete under your feet. It’s strange but the cold just seems to radiate up through your shoes to make you feel cold – too cold. Since I’ve already resigned to the fact that my garage budget was blown I knew I wanted to install radiant floor heat into the garage.
How Radiant Floor Heat Works
In layman’s terms this system is essentially really simple. Heated liquid which is a water and antifreeze mix flows through the concrete floor warming it up to a pleasant temperature. Once heated the concrete radiates the warmth into the air of the garage warming the whole place up. Concrete is very good at retaining heat which makes it very efficient keeping the cost of heating down. This does also require good insulation so heat loss is minimal.
Insulation
The garage is well insulated. R-19 is installed in all of the walls as well as R-38 in the ceiling. The large garage doors as well as the side door are insulated. The concrete floor has 2″ thick foam insulation surrounding the sides as well as a 2′ perimeter below the concrete. This keeps the concrete from direct exposure to the cold.
Floor Tubing
Before concrete is poured loops of tubing are attached to a grid that will be embedded in the concrete. The tubing used in my installation (and many others) is called PEX-AL-PEX. PEX-AL-PEX is aluminum reinforced PEX tubing. PEX is a polyethylene composite material that is commonly used in plumbing. The aluminum reinforcement helps the tube retain its shape when it’s embedded into the concrete. In addition the aluminum helps with heat transfer.
The tubing is laid out in a pre planned manner to create zones keeping the total length even and to a maximum. This allows for even heat distribution and efficiency. Depending on the size of the floor the number of zones will vary. In my case there are three zones.
Distribution Manifold
The floor loops are attached to a distribution manifold. The manifold takes the flow in and flow out from the heat source and allows for regulated distribution through the loops. In some cases you may want to increase or decrease flow of the liquid using the regulators to change the heat level of the zone.
Heat Source
This part has many options of how to do this and a types of heat “fuel” to use. At the end of the day the goal is to head the liquid and pump it through the tubing. Natural gas, propane, heating oil and electric are the most common methods and each has its advantages and disadvantages. This is something that will have to fit your particular situation.
In my case electric made the most sense. Electric heat isn’t the evil it once was since now everything is expensive. I don’t have a natural gas option and I didn’t want to deal with a propane tank or heating oil tank and the things that come with those two options. Electric prices are pretty stable and regulated as well as electric will already be in the garage for everything else. Maintenance of an electric heat system is rather simple and reliable.
Heat System
In my research I’ve seen many versions of home grown heating systems but I didn’t want to mess around with a system so I left the design to a well known company. Stiebel Eltron makes a ready to install system that was matched to the size of my garage. I purchased this directly from them. The HydroShark Pro Panel on-demand heat system contains all of the needed components such as the boiler, circulator and expansion tank. In addition all of the plumbing including valves, filters and fittings are all set up and ready.
The entire unit is mounted to a steel panel that is ready to be attached to a wall and plumbed into the distribution manifold. The boiler requires a 220v circuit and the circulator pump system requires 110v. My system uses a 7kW on-demand boiler that heats the liquid as it’s flowing through. A separate thermostat controls the operation of the whole unit.
I mounted the unit to the wall studs directly above the distribution manifold. The unit has input and output fittings that are 1″ Shark Bite fittings. The manifold uses 1″ fittings as well so it just required some PEX tubing, a few 90 degree fittings and two PEX to NPT adapter fittings.
Antifreeze
Once the system was attached to the manifold I was ready to add the liquid. I used a premixed antifreeze that is designed for these type of systems. This antifreeze isn’t the same that is used in automobiles, it’s closer to RV style antifreeze, I used Cryo-Tek propylene glycol. This antifreeze is available from retail DIY home stores and from supply houses. I calculated that my system would need about 7+ gallons of liquid. I purchased a 5 gallon bucket along with three one gallon bottles.
Filling Up the Heat System
The Stiebel Eltron system included some thorough directions and it was suggested to use a transfer pump to pump the liquid through the system. I purchased a pump that could attach to garden hose style fittings. There are fittings that are included in the system that are used for filling and pressurizing the system. A hose from the 5 gallon bucket is attached to the pump. Then the output of the pump is attached to the input fitting on the radiant floor heat system. Another hose is attached to the return to allow the fluid to return to the bucket.
The process of adding the fluid requires circulation time. This takes a bit of time and allows the constant flow of fluid to make sure all of the loops are filled and air is purged. Add more fluid to the supply as needed to prevent it from running out and pumping in air.
Pressurizing
Once the system is filled and air is purged the last step is pressurizing. The transfer pump is capable of providing the needed pressure for proper system operation. This is done by closing the return valve while the pump is still running. Once the desired pressure is achieved close the input valve and shut off the pump. Repeat the pressurization if needed. In my case I did need to pressurize it a second time most likely due to air bubbles. UPDATE: It’s been 6 months since the system was pressurized and it is still at the same pressure. If you see constant pressure drops it can mean there is a leak.
Thermostat
The Stiebel Eltron system can use a standard thermostat for operation. Since I have a bit of a tech bug I used a smart thermostat from Amazon. This thermostat integrates with Alexa and can give nice data to monitor the heat of the garage. See the full article – Amazon Smart Thermostat article on 7sGarage.com.
Radiant Floor Heat Usage and Performance
Radiant floor heat systems do not heat quickly and are best left set to a specific temperature. In addition it’s most efficient if it is left on all of the time. Basically never let the floor get cold and the system will work exceptionally well.
My garage is set to 58 degrees which is a nice temperature to work at with a sweatshirt on. If I ever feel I need it warmer quickly (this happened once all winter) I use a kerosene torpedo heater to heat the air quick. I could see myself installing a split system air conditioning/heat pump system some day. The heat pump would work great to warm the air a bit if needed.
It’s real interesting how well this works, it’s better than I expected. The floor is really never “warm” but it’s definitely not cold. That’s what’s important here. The concrete just feels room temperature and that is what works with this setup. The boiler only heats the fluid to 120 degrees, just enough to keep the concrete warm. I’ve found on average the heat may only run about a few hours a day when it’s really cold.
Final Thoughts
I’m glad I took on the extra expense to do this since it performs so well and seems to not impact my electric bill. I’d like to believe the efficiency of the system will pay for itself over time. Since most of the work I do in the garage is in the winter when it’s off season I wanted it comfortable when I need it.