Buying a furnace is not something most people do often, so the terminology and options can feel overwhelming. Focus on three things — efficiency, sizing, and fuel — and the decision gets much clearer.
1. Efficiency (AFUE)
AFUE (Annual Fuel Utilization Efficiency) measures how much fuel becomes usable heat. A 95% AFUE furnace turns 95% of its fuel into heat. Higher efficiency costs more upfront but lowers your bills. In Colorado's long heating season, a high-efficiency unit often earns back the premium — but the right level depends on your budget and how long you plan to stay in the home.
2. Sizing
This is where a lot of installs go wrong. An oversized furnace heats too fast, shuts off, and short cycles — wearing itself out and heating unevenly. Undersized can't keep up on cold nights. Proper sizing comes from a load calculation that accounts for your home's square footage, insulation, windows, and layout. Be wary of anyone who sizes by rule of thumb.
3. Fuel and system type
Most Colorado homes run gas furnaces, but it is worth knowing your options — including whether a heat pump or hybrid system might fit your home better. That companion guide walks through the tradeoffs at altitude.
What else matters
- Warranty: Understand the parts and labor coverage and what registration requires.
- Installation quality: A great furnace installed poorly underperforms. The installer matters as much as the equipment.
- Financing: For a major purchase, ask about financing options.
The honest approach
A trustworthy company runs a real load calculation, explains the efficiency tradeoff in terms of your actual bills, and gives you options from premium to economical without pushing the priciest one. See our heating installation services for how Smith approaches it.
Frequently asked questions
What furnace efficiency (AFUE) should I get in Colorado?
Most new high-efficiency furnaces run 90-98% AFUE. Higher efficiency costs more upfront but burns less fuel. In our cold climate, a high-efficiency furnace often pays back the difference over its life, but the right level depends on your home and budget.
What size furnace do I need?
Bigger is not better. An oversized furnace short cycles, wears out faster, and heats unevenly; undersized can't keep up. Proper sizing comes from a load calculation based on your home's size, insulation, and layout — not a rule of thumb.
How long does a furnace last?
Typically 15 to 20 years with regular maintenance. If yours is in that range and needing repairs, it is worth weighing replacement against continued fixes.