Furnace type
Single-stage furnaces
A single-stage furnace has one gas rate: full fire on every call until the thermostat is satisfied. It is the least expensive type of 95%+ furnace, and it is a perfectly honest choice for small or steady heat losses, at the cost of temperature swing and full-fire cycling.
Short answer
Single-stage means one gas rate: the burner fires at full input on every call. Every new furnace sold in Canada is at least 95% AFUE regardless of staging, so a single-stage furnace is efficient; what it lacks is low-fire operation, which two-stage and modulating furnaces use on mild days for steadier, quieter heat. Correct sizing matters most on single-stage furnaces because there is no low stage to soften an oversized burner.
How single-stage operation feels
The furnace runs flat out until the thermostat is satisfied, then stops. On mild days that means shorter, harder cycles, and rooms cool a little between cycles before reheating. For a well-insulated house with a small, steady heat loss, the effect is modest; for a large or variable-load house it is the difference between acceptable and drafty-feeling heat.
Where single-stage fits
Entry tiers of every major brand are single-stage: on this site, for example, Carrier's Comfort 96 and its single-stage Performance 96 are both one-gas-rate furnaces. They cost less than their two-stage siblings and have fewer parts to fail, which is a real advantage, not a marketing footnote.
Sizing matters more
A two-stage furnace can partly absorb oversizing by running low fire; a single-stage furnace cannot. An oversized single-stage furnace short-cycles on full fire, which is why the heat-loss calculation is not optional for this type. Manufacturer product data used across this site warns that excessive oversizing can shorten furnace and vent life.
Related
- ServiceFurnace Purchase AdviceIndependent-minded furnace buying advice before you sign anything
- ServiceGas Furnace InstallationNew furnace installation sized from a heat-loss calculation, not from the old furnace
- ServiceGas Furnace ReplacementReplace an aging or failed furnace with the right high-efficiency furnace for your house
Questions people ask
Is a single-stage furnace less efficient than a two-stage?
No. Both are certified by AFUE, and single-stage furnaces reach the same 95%+ figures (Carrier's single-stage Performance 96 certifies up to 97% in some sizes). Efficiency and staging are different things.
Why would anyone buy a single-stage furnace?
Lower first cost, simplicity and fewer parts. For a steady heat loss in a compact house, it delivers the same gas efficiency as a two-stage with less to go wrong.
Can I add low-fire operation later?
No. Staging is built into the gas valve and control. Changing types means replacing the furnace.
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