You Don't Have to Heat the Whole Driveway

Most people who call me about a heated driveway describe the whole slab. Every square foot of it, plus the walk, plus the apron down to the street.

That is one version of the system. It is not the only one, and it is often not the one that gets built.

The other version heats the parts you actually use — two tire tracks into each garage bay, and the path from the driveway to the front door. The rest of the concrete stays cold and gets shoveled the way it always has.

I now draw both on every residential driveway I look at. Here is the reasoning, including the part that surprises people.

Snowmelt is a big load, and that sets everything else

A heated driveway is not a warm floor moved outdoors.

Run the numbers for the Front Range and a snowmelt slab lands around 130 BTU per hour per square foot at design conditions. A whole house on the same street runs 25 to 40 BTU per hour per square foot — that is the entire house, envelope and all.

So a moderate driveway can ask more of a boiler than the home it sits in front of.

That number also does not come from the temperature your furnace was sized on. Snowmelt is sized on the weather during a snow event — air temperature, wind, and snowfall rate happening at the same time. It is a different calculation with a different answer, and reading it off the winter design temperature is the most common way these systems end up undersized.

Where the cost actually sits

Here is the part that surprises people, which is why I put it in writing before anyone has to ask.

Cutting the heated area in half does not cut the price in half.

The boiler, the gas line, the mixing assembly, the control, the slab sensor, the mechanical room work, and the permit are all fixed. They come with the system whether you heat 700 square feet or 2,000. What shrinks is tube, manifold ports, insulation, and field labor.

Priced honestly, a priority zone at roughly a third of the area comes out closer to half of the full system — not a third of it.

Narrow strips close that gap further. Tire tracks run about two and a half feet wide, two per bay, and a narrow strip carries more edge and more supply-and-return run per square foot than an open field of tubing does. That is why I take tube counts off the drawing rather than multiplying area by a rule of thumb.

None of that makes the smaller system a bad decision. It makes it a decision you should get to make with the real number in front of you.

Why I would rather re-scope than discount

A discount does not change what gets built. It moves money around and leaves the same system on the drawing.

Re-scoping changes the thing itself. A priority zone is a smaller system, engineered for the job you care about most — get the cars in and out, keep the walk to the door clear — with a boiler sized to that smaller load instead of an oversized one hunting at part load all winter.

It is also the version that can grow. If the manifold and the sleeves are set up for it, the balance of the driveway can be added later, whenever that concrete comes out for some other reason.

What I put on paper

On any residential driveway, you get two prices before anything is issued:

• Full coverage — the whole drive, walks, and apron as one heated surface.

• Priority zone — tire tracks into each bay plus the main walk, or whatever the daily path actually is on your site.

Both are drawn on the same zone map, the priority zone solid and the balance dashed with its add rate. You see the trade-off early, not while a concrete crew is waiting on a schedule.

Two things that do not change either way

Loop length. I cap loops at 200 feet of half-inch tube and 250 feet of five-eighths. A loop longer than that gives up too much temperature down its length, and the far end stops melting. That holds whether you heat the whole drive or two strips.

Insulation under the slab. Heat travels down as readily as it travels up. Under a snowmelt slab, insulation is not an upgrade line — it is the difference between melting snow and heating dirt.

The timing part

Tubing goes in before the pour. There is no version of this that gets added afterward without taking concrete out.

If a driveway, patio, or walk is being poured on your property this fall, that is the window, and the design has to be done before the forms go up.

Send me the dimensions of the area you are thinking about and I will tell you what it takes to heat all of it, and what it takes to heat the part you use. Both numbers, before you decide.