DIY Heated Garage Floor

DIY Heated Garage Floor (Hydronic Floor Heat)

Heated Garage Floor for Fixing Things

The secret to living in Podunk USA is being able to fix just about anything. In order to fix things, you’ll need tools. In order to find your tools when you need them, you’ll need a garage or shop. When things break in the winter, fixing them in a heated shop is better than in outside in cold, frigid temperatures.

Heating the Garage, Radiant Style

When we started to fix up our old pole barn to turn it into a machine shop, it didn’t take long for us to decide that we would install a hydronic radiant heat system. Hydronic in-floor heat systems are one of the best ways to heat a large garage or shop area, because the heated floors warm the items in the area and not just the air (like forced air furnaces). When the concrete floors act as the radiator, the room temperature will quickly return to normal when the garage doors are opened and closed in cold months. When using radiant heat flooring as a primary heating system, make sure to install hydronic systems instead of electric radiant heating systems. Hydronic radiant floor systems don’t necessarily create warm floors, like electric radiant floor heating. Electric radiant heat is more useful to warm the floor of a bathroom, already heated by the home’s primary HVAC system.

converting pole barn to heated garage

Shop Floor Heat Preparation

The first thing we needed to do to install the in-floor heating, was cut out an overhead door. We then framed in the garage door opening, and prepped it for a future overhead garage door.

preparing post frame building for hydronic radiant heat

Ground Preparation for the Heated Concrete Floor

The next step to installing a heated concrete floor, was to level the ground inside of the building and build a ramp into the new door. Over 50 years of animals living in this 3-sided barn, required scooping out a lot of dirt and manure. In fact, the ground was so hard from the animals packing down the dirt, the skid loader couldn’t dig it deep enough to level half of the building. We ended up having to jackhammer and dig out 6″ of dirt by hand.

leveling floor of old pole barn

Garage Floor Drain for Snow Melt

We also decided to put a drain in the shop, for snow melt-off from vehicles in the heated garage. So we dug the trench under the wall and ran the drain down the hill to daylight.

heated garage floor,heated shop floor,diy radiant floor,hydronic radiant heat

Under-Slab Insulation For Garage Floor Heating

Once the grading was done, the ground was level, and the drain pipe was installed, we laid the subfloor insulation and taped the seams. We used Owens Corning® FOAMULAR® 250 R-10 Extruded Polystyrene Foam Board Insulation, which is designed for use under garage floor heat. At nearly $60 per 4′ x 8′ board, it was very expensive (and took multiple trips to transport it all). I did HOURS of research to see if we could use a cheaper insulation board. However, the problem is that a minimum strength of 25 PSI is needed for under a garage concrete slab, to withstand the pressure of a vehicle on the concrete. Insulation under the cement is important to push the heat up into the garage, instead of heating the ground below. The Owens Corning board was the cheapest I could find that was acceptable for use under our heated garage floor. The last thing we would want was to try to save a few hundred dollars on insulation, to have it cave in and crack our concrete and ruin our hydronic heating systems.

setup for in floor heated garage

Radiant Floor Heating Zones

Once the insulation was laid, we ran the oxygen barrier PEX pipe (Amazon affiliate link), which is what will heat the floor. We used 1/2” pipe, spaced 8” on center, with a max of 300’ loop per zone. The easiest way to determine how many heat zones we needed was to take the room length (in feet), and multiply it by 12” (to get the room length in inches). We then divided the room length (in inches) by the 8” spacing (on center). This told us how many runs of pipe we needed. We took the number of runs of PEX, and multiplied it by the width of the room in feet, which told us how much tubing we needed for the project (in feet). We divided the total number of PEX pipe needed by 300 feet (300 feet of PEX pipe per zone as a maximum, so that the temperature doesn’t drop too low from the beginning of the zone loop at the heat source to the end of the loop return). We rounded the results up to the nearest whole number, which is the number of heat zones we needed for the project.

Pex and insulation for heated garage concrete floor

Radiant Floor Heating System before Pouring Cement

We laid out our heat zones so that 2 zones were next to each other, in case one heat zone were to break, the other heat zone could still heat the area (heating 16″ on center instead of 8″, and minimizing cold spots). We held the PEX pipe in place with PEX staples. You can place the staples by pushing them into the under slab insulation foam boards by hand, however, with a large square feet area, I would invest in a staple gun (Amazon affiliate link). Once the PEX tubing was laid and stapled into place, we laid the rebar on top. We laid the rebar on top of the PEX to hold it up off of the foam board, allowing the concrete to completely surround the rebar (and to prevent having to buy rebar spacers). There are 2 small squares where we did not run the hydronic radiant floor heating systems, these were marked and measured to hold a 2 post car lift later. We decided that we would need 8″ of concrete with rebar for that area, to hold the weight of most vehicles and/or future equipment we may purchase later on.

Concrete truck with telebelt to spread cement over in-floor radiant heat

Pouring the Concrete Floors

We were now ready to pour the concrete pad. Before cement day, we pressurized the PEX lines with air and installed cheap gauges so that we could see if the PEX could maintain pressure. If the pressure dropped, we would know when we should stop pouring concrete and find the break in the line before the concrete set. We then poured 4″ of concrete over top of the insulation, surrounding the hydronic radiant floor system and the rebar (to prevent cracking). We had a concrete telebelt truck transfer the wet concrete from the concrete truck, and disperse it throughout the shop. The rebar and PEX pipe prevented us from being able to move the concrete with wheelbarrows or a concrete buggy, so the telebelt truck was a necessary expense. We also placed some leveling posts in the middle of the shop, to help us ensure that the new concrete floor would be level (this was an essential time saver when pouring this much concrete in one long pour). We also covered the drain pipe securely with tape, and made sure to uncover it before the concrete floor started setting up.

Pouring concrete over hydronic radiant heat

Heated Garage Floor System

Once the concrete started to cure, we checked our gauges. Luckily we had no drop in pressure, and we were good to continue installing the floor heating system! The next step was to assemble the manifold, pressure release valve, mixing valves, pumps, and install the boiler. We decided to use a good propane boiler, and not go cheap on an electric boiler or water heater. Trust me, it was extremely difficult for my frugal self to spend more money on a heater. When the temperatures in the shop are able to remain consistent (even during a Polar Vortex), and we are able to continue to work on projects all winter, believe me, IT IS WORTH THE PRICE! I have seen a number of electric boilers and hot water heater listings on Facebook Marketplace by the end of winter that has been used in a hydronic floor heat system, because they don’t quite work in the bitter cold winters of the midwest. That was enough evidence for me to know to spend the money on a good propane (or natural gas) boiler for radiant garage floor heating.

Power troweling in-slab radiant heat
MaterialCost EachTotal Cost
250 Extruded Insulation Boards$56/each$3150
1/2″ Rebar Spaced 18″$8.49/each$1018.80
Oxygen Barrier Pex 300′ Loops$114.99/each$1034.91
PEX Staples$49.99/box$99.98
Cement (cash discount)$109/yard$2188.20
Total Cost$8241.89
The national average cost to have a company install radiant floor heat is $8-$20/sq ft, or $14,400 – $36,000.

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