Electric boilers are simple, quiet and clean. No gas line, no venting, no chimney. They are also the radiant heat source most often bought too big.
An electric boiler needs electrical capacity for its full size, not what the house actually uses. Buy one twice too big and you lose half your panel. Here is how to size it, and when something else makes more sense.
Start with the CSA F280 heat loss at your design temperature. Divide the BTU per hour by about 3,412 and you have kilowatts. That is the size the house needs on the coldest day.
A 24 kW electric boiler draws about 100 amps at 240 volts. If the house only needs 12 kW, half of that capacity sits there doing nothing except blocking your heat pump, EV charger or hot tub.
Picking the boiler from the catalogue or the old system, then discovering it needs most of a 200 amp service. Do the heat loss first.
ICF and high-performance homes with small loads make electric boilers much more reasonable to run.
Simple, no venting, and the load is often modest. See heating a garage or bunkie.
Electric elements or a small boiler as backup for an air-to-water heat pump.
A slab holds heat. Some owners use Ontario’s overnight price plans to heat more at night.
No boiler size without a heat loss.
Boilers with stages or modulation match the load better.
Give your electrician the real kW before anything is ordered.
Air-to-water uses a fraction of the electricity. See air-to-water.
The boiler is one piece. Tube spacing, loop lengths, manifolds, slab insulation and controls decide whether the floor actually heats the house. See radiant floor design and boiler sizing for radiant.
If the boiler is the main heat for a house, expect a building permit with the heat loss, the radiant design and the ventilation summary (RMVDS), plus an ESA electrical permit.
Planning electric radiant? Send the drawings. We size the load so the boiler fits the house and your panel.
Get Free Quote →The size comes from the heat loss. Divide the design heat loss in BTU per hour by about 3,412 to get kilowatts. A boiler much bigger than that just ties up your electrical service for nothing.
Because it needs a breaker and service capacity to match its full size, not what the house uses. A boiler twice the size it needs can take the room you wanted for an EV charger or a heat pump.
They turn each unit of electricity into one unit of heat. Cheaper than nothing, dearer than a heat pump. A tight house with a small load makes them much more reasonable.
A heated slab has a lot of thermal mass, and Ontario has time-of-use and overnight price plans. Some owners heat the slab more overnight. Whether it saves money depends on the house, the slab and the rate plan.
A heat pump makes two or three times more heat per unit of electricity on most days, but costs more to install and needs a proper design. See air-to-water heat pumps.
If the boiler is the main heat for a house, expect a building permit with the heat loss and radiant design, plus an ESA electrical permit. A heated garage or shop may be treated differently. Ask your building department.
Send your drawings. We calculate the heat loss and design the radiant system, with the boiler sized to the house, not the catalogue.