Staging is how the burner fires. The blower is how air moves, across the heat exchanger in winter and across the AC coil in summer. You choose them separately.
Single-stage, two-stage and modulating
- Single-stage runs at full fire until the thermostat is happy, then shuts off. On mild days that means short, frequent cycles.
- Two-stage has a low fire of about two thirds and spends most of the winter there, stepping up on the coldest nights.
- Modulating turns the flame up and down in small steps, from about 40% to 100%, and runs long and low.
A furnace sized for the coldest Denver night is oversized for almost every other hour. Staging gives you longer runs, fewer starts and less difference between rooms.
The blower
- Multi-speed motors have a few fixed settings. They come on most single-stage furnaces.
- Variable-speed motors hold steady airflow as the filter gets dirty and ramp with the burner. They come on most two-stage and modulating furnaces.
If you have central air, the blower also moves the cooling air. If you might add a heat pump later, get variable-speed, because an inverter heat pump changes speed all day and the airflow needs to follow it.
When the ducts are the problem
Small returns, crushed flex duct or one return for the whole house will make any furnace loud. Ask for a static pressure reading at the estimate. Most furnaces are built for about 0.5 inches of water column, and a reading well above that means the ducts need work. A room that is cold today will stay cold if the duct to it is the problem.
Send photos of the furnace and the ducts around it, or schedule an estimate.
Common questions
Is a modulating furnace worth it in Denver?
It is the most even and the quietest, and it costs more. Two-stage gets most houses most of the comfort. Modulating pays off in larger or zoned houses and in rooms that run cold.
What is static pressure?
It is how hard the ducts push back against the blower, measured in inches of water column. Most furnaces are built for about 0.5 inches total.