Radiant Floor Heat for Garages: Zoning, Insulation & Boilers

Designing Hydronic Radiant Floor Heat for a Garage or Shop

We recently got a call from a homeowner — let’s call him Mike — who was building a new 50' x 60' shop. He told us, “I’m tired of burning wood in a stove just to keep the chill off. I want hydronic radiant floor heat in the slab so the whole building stays comfortable.”

Mike had about a foot of depth to work with in his slab build-up, a planned bathroom with a shower, and he was wondering about zoning, insulation, and what kind of boiler would make the most sense. That conversation is a good blueprint for anyone planning radiant floor heating in a garage or workshop.

How Many Zones Does a Garage or Shop Really Need?

One of Mike’s first questions was, “Do I really need more than one zone?” His shop will mainly be used for storing vehicles and equipment, with a bathroom in one corner and some light work here and there.

In that kind of setup, one zone is usually plenty. Here’s why:

• Even temperature: A wide-open garage or shop naturally equalizes temperature. Splitting it into multiple zones often doesn’t give you much practical benefit.
• Simpler system: One zone means fewer manifolds, valves, controls, and potential failure points — and lower upfront cost.
• Easy setback: You can still turn the entire space down when you’re away and keep it just above freezing with a simple thermostat.

Where multiple zones do make sense is when:

• You have very different uses in the same building (for example, a warm office or hobby room and a cooler storage bay).
• There are areas you want to shut off entirely most of the time.
• You have large south-facing glass or other spaces that overheat while others stay cool.

For Mike’s wide-open shop with one bathroom, we recommended one simple zone tied to a single thermostat — with the option to add a backup or secondary heat source later if he ever wanted to keep the shop cooler but the bathroom a bit warmer.

Insulation & Tube Layout: The Foundation of a Good System

After zoning, we walked Mike through how we like to build the slab. He had about a foot of depth to work with, which is more than enough for a solid radiant design. The most important piece here is insulation.

Why We Insist on 2" Foam Under the Slab

We told Mike exactly what we recommend on almost every garage and shop project:

• 2" rigid foam insulation (commonly EPS or XPS) across the entire slab area.
• Foam under the slab and at the slab edges to cut heat loss into the ground and to the outside.

That 2" foam does a few critical things:

• Keeps more heat going up into the space instead of down into the soil.
• Makes the system much more efficient, especially if you use a condensing boiler.
• Helps stabilize slab temperature and reduces cold spots.

Skipping or thinning the insulation is one of those “savings” that costs you in fuel and comfort for the lifetime of the building.

Mesh, Tubing, and Rebar: Don’t Bury Problems in Concrete

We also shared with Mike how we like to secure the tubing:

• Lay down the 2" foam.
• Install 6" x 6" welded wire mesh on top.
• Zip-tie the PEX tubing directly to that mesh so every loop has a positive attachment point.

Concrete crews love their rebar, and that’s fine — as long as it doesn’t interfere with the tubing. A common shortcut is to tie the tubing directly to the rebar. We avoid that, and here’s why:

• When you tie tubing to rebar, it often ends up too close to the slab surface.
• That increases the risk of hitting tubing during saw cuts or anchor drilling.
• We want the tubing deeper in the slab, not right where tools are going to cut or drill later.

Our approach lets the concrete crew place the rebar above the tubing where they like it, while keeping the PEX safely lower in the slab. It’s a little extra coordination, but it protects the system long-term.

Boiler Choices: Space Heating Only vs. Combi Boiler

Once we covered the slab details, Mike asked us to “factor in the boiler and the whole nine yards” and mentioned the planned bathroom with a shower, sink, and toilet. That opened the door to a great option: a combi boiler.

When a Combi Boiler Makes Sense

A combi boiler is a single appliance that does two jobs:

• Heats the water for your radiant floor system.
• Provides domestic hot water for showers, sinks, and other fixtures.

For a garage or shop with a bathroom (like Mike’s), a combi setup can be ideal:

• One appliance instead of a separate boiler and water heater.
• Highly efficient, especially in a well-insulated slab system.
• Endless hot water (within the boiler’s capacity) for showers and handwashing.

We often prefer a high-quality combi boiler over standard on-demand water heaters because they’re designed to handle both space heating and domestic loads reliably, with better controls and often longer life when properly installed.

Where to Put the Boiler and Controls

In Mike’s plan, we’re tucking the boiler and related piping under a stair area at the back of the shop. That kind of location works well if:

• There’s enough clearance for servicing the unit.
• Venting can run to an exterior wall or roof without a maze of elbows.
• You have a nearby water supply and drain for the domestic hot water side and condensate.

Wherever the boiler lands, we also plan space for the manifold(s), circulator pump(s), and a simple, easy-to-use thermostat for the zone.

Who Should Handle What: DIY vs. Pro Work

Mike was comfortable coordinating his own concrete contractor and even offered to handle laying the foam and mesh if it made sense financially. That’s a perfectly reasonable approach on many projects.

Here’s how we often split responsibilities on a garage or shop:

• Homeowner/GC: Site prep, foam installation (with our layout guidance), mesh placement, and coordinating concrete pour.
• Our team: System design, tube layout, tubing install and pressure test, boiler and controls installation, start-up, and balancing.

You’re free to do as much or as little as you’re comfortable with, but be aware: anything that gets buried in concrete (especially the tubing) is worth doing carefully and correctly the first time.

Planning Your Own Radiant Shop or Garage

If you’re like Mike and you’re building or rehabbing a garage or shop, a well-designed hydronic radiant floor can turn it into a truly usable, comfortable space — without the hassle of a wood stove or the draft of overhead heaters.

The key decisions you’ll want to think through ahead of time are:

• How many zones you realistically need.
• How much insulation you’ll commit to under and around the slab.
• Whether a combi boiler makes sense for your hot water needs.

If you’re planning a project like this and want a design that’s efficient, comfortable, and built to last, we’re always happy to walk through the details and put together a system tailored to your space.