Furnace salesmen love this question because the answer they give always costs more. The honest answer is simpler: it depends on how much heat your house actually needs and how much that need swings between a mild November day and a -25 C January night.
Here is what each type does, which houses each one fits, and why a tight new house can be a problem for a regular furnace.
On full, or off. Like driving everywhere with the gas pedal on the floor and then coasting. Simple, cheapest, and fine when it is sized right.
A low fire for most days and a high fire for the cold ones. Longer, quieter, steadier cycles. A good middle ground for most houses.
Turns up and down in small steps to match what the house needs right now. The smoothest and quietest, and the best fit for small, tight houses.
Design day is maybe a handful of nights a year. The rest of the winter your house needs much less. A furnace that can turn down spends more of its life matching the house instead of blasting and shutting off.
A right-sized two-stage often gives you most of the comfort for less money.
Modulating, or look hard at a heat pump. A regular furnace may be bigger than the house needs even at its smallest.
Small loads and long, even demand. Modulating or a heat pump fits best. See ICF heat loss.
A properly sized single-stage beats an oversized modulating furnace every time.
A modulating furnace twice the size the house needs still short-cycles. Size first, then pick the type.
Low fire means lower airflow. Weak ducts show up as cold far rooms. See duct design.
Top-tier controls on a house that needs a fraction of the furnace’s output. Spend the money on the right size.
Choosing the type without knowing the load. That is shopping for tires without knowing the car.
The CSA F280 heat loss tells you two things: how much heat the house needs on design day, and from that, how small the furnace could be. Once you know that, the type is an easy decision. Also see why rules of thumb oversize furnaces.
Comparing furnace quotes? Get the heat loss. Then every quote can be checked against the same real number.
Get Free Quote →No. The code cares that the furnace is efficient enough and big enough for the calculated heat loss. Single-stage, two-stage and modulating can all pass. The choice is about comfort, noise and how well the furnace fits your house.
In a tight new house or an ICF home with a small heat loss, often yes. It can turn way down on mild days instead of blasting and shutting off. In a drafty older house with a big load, a two-stage unit gets you most of the benefit for less.
It happens more and more in new, well-insulated houses. A modulating furnace that can run very low helps. So does looking at a heat pump or a combination system. The heat loss tells you how big the gap is.
A little, mostly through longer, steadier cycles. The bigger win is comfort: fewer temperature swings, quieter operation and better air mixing. The biggest gas saving still comes from sizing it right in the first place.
New residential gas furnaces sold in Canada have to be high-efficiency condensing units. In practice that means about 95% AFUE or better. Check the rating on any furnace you are quoted.
No special ducts, but the ducts still have to be designed properly. A modulating furnace running at low fire moves less air, so a good duct design matters even more to get heat to the far rooms.
Send a floor plan or drawings. We calculate the heat loss room by room so you can pick the right furnace type and size.