Boilers, Radiant Floors and Hot Water in Ontario (2026): The Best Heat Source for Radiant, Combi Boilers, Air-to-Water Heat Pumps, Radiant Problems, Tankless and Rental Water Heaters

Heating, Cooling & VentilationHydronic and hot water

Boilers, Radiant Floors and Hot Water: The Floor Is the Heater, the Boiler Is the Engine, and the Two Have to Be Sized for Each Other

Radiant floor cost and design, heat sources, combi boilers, air-to-water, radiant problems, tankless and rental water heaters. Central Ontario, October 2026.

I have put hydronic radiant floors in houses since the early 1990s and I still think it is the best heat there is. It is also the system where a quote can look complete and leave out half the job: the floor without the boiler, the boiler without the controls, a combi sized for the showers that short-cycles on the floor all winter. This section is how to tell the difference, and how to pick the heat source the floor actually wants.

Compare five systems Heat sources for radiant Size the hot water

The numbers

Central Ontario, installed, before HST, checked October 2026. Published prices for the same job vary widely; these are the defaults the calculators use.

$9per sq ft, radiant tubing in a new slab ($6 to $12)
$7,500combi boiler, replacement ($5,000 to $10,000)
$15,000+air-to-water plant, quoted individually
4.8 gpmwhat a 199,000 BTU unit heats from 5 C to 49 C

The guides

Radiant floor heating cost

Already on the site: tubing per square foot, the whole-house system, retrofit, toppings and running costs.

The best heat source for radiant floors

Condensing boiler, combi, air-to-water, geothermal or electric boiler, by install cost, running cost and what we put in.

Combi boiler cost

The replacement price, the complete combi mechanical room, what belongs in each quote, and the houses a combi suits.

Combi boiler vs tankless water heater

One appliance or two in a radiant house: hot-water priority, winter flow, venting, cost and service.

Air-to-water heat pumps

Output at minus 25, supply-water temperature, buffer tanks, defrost, backup, hot water, cooling, cost and who installs them.

Radiant heating design

Already on the site: the heat loss, loop layout, manifolds and the permit package.

Radiant floor heating problems

Cold zones, air in the loops, short-cycling boilers, slow response: what you can check and what needs a technician.

Tankless water heaters

Already on the site: when tankless makes sense, when a heat pump water heater beats it, and sizing basics.

Rent or buy a water heater

The monthly cost, the 15-year arithmetic, buyouts and removal fees, the door-to-door rules and how to get out of a rental.

Radiant floor cooling

Already on the site: what a floor can and cannot do in July, and the dew point.

Rules I give every customer

  1. Size the boiler to the heat loss, not the hot water. A combi big enough for three showers is usually far too big for an ICF slab; its turndown decides whether it short-cycles. Combi or tankless.
  2. Run the floor as cool as it will go. Low supply-water temperature is what makes a condensing boiler condense and an air-to-water heat pump efficient. Radiant design.
  3. Insulate under the slab. R-10 under a heated slab or you are heating the ground. Slab insulation.
  4. Plan the cooling and the HRV on the same day as the floor. Radiant does neither. Ventilating a radiant house.
  5. Read the water heater rental contract before you sign anything at the door. Door-to-door contracts for water heaters are banned in Ontario unless you called first. Rent or buy.

Have quotes in hand? Let a builder read them first

For $99, I put up to three heat pump, furnace, boiler, AC, HRV or water heater quotes on one grid: whether a heat loss was done, the model numbers checked against the cold-climate list, the capacity at your design temperature, what each one left out in dollars (ducts, electrical, condensate, venting, commissioning, the old unit), the rebate claim checked, and a plain answer on which to sign. No contractor behind it and no commission on who you hire.

HVAC quote review, $99 Heat loss and HVAC design Check the quotes yourself first

Sources and further reading