Replacement, addition, or new construction
Furnace installation covers more than just replacing a dead unit — the sizing and planning differ depending on why you’re installing.
Replacing a failing furnace
A heat exchanger crack, repeated repairs, or a unit over 15 years old often makes replacement the better financial decision — see our repair vs. replace guidance →.
Room additions
New square footage needs its own heating capacity calculation — tying into an existing furnace often means the addition and the original rooms both end up undersupplied.
New construction
Ground-up builds need a furnace sized to the actual house — insulation, square footage, and window placement all factor into a real load calculation, not a rule-of-thumb size.
Why the wrong-size furnace is worse than the old one
An oversized furnace short-cycles — it heats the air fast but shuts off before the home actually reaches temperature evenly, and the constant on-off cycling wears out components faster than steady operation would. An undersized furnace runs constantly and never quite catches up on the coldest nights. We calculate the correct size for your specific home — square footage, insulation, ductwork condition — before recommending equipment, not after you’ve already agreed to a number.
What Fresno homeowners say
4.8 stars across 1,200+ verified Google reviews — Fresno, Clovis, Madera, Sanger, Selma, and surrounding Fresno County cities.
They replaced our old furnace and checked the heat exchanger for carbon monoxide at the same time. House heats up twice as fast now and I have video proof of every step.
Our old unit was on its last leg — Grandmark showed us the numbers on video and it was clear repair wasn’t worth it anymore. New system installed same week, no pressure the whole time.
Three companies gave me quotes without even looking at the system. Grandmark ran a diagnostic and found the real issue. Saved me over $2,000 and my system has been perfect ever since.
We’ll respond in 20 minutes or less
Tell us about your home and current heating situation, and we’ll schedule your free in-home estimate. During business hours, that’s typically within 20 minutes.
Furnace installation FAQ
How long does furnace installation take?
Most standard installations are completed in 4-8 hours for a straightforward replacement. Installations requiring ductwork modifications or new construction typically take longer, depending on scope.
What size furnace do I need?
It depends on square footage, insulation, window orientation, and ductwork condition, calculated through a real load calculation — not just matched to your old unit’s rating. An oversized furnace short-cycles and wears out early; an undersized one runs constantly and never quite keeps up on cold nights.
Should I repair my furnace or install a new one?
Generally, repair makes sense if your furnace is under 15 years old and the repair cost is reasonable relative to replacement. Replacement usually wins for a cracked heat exchanger, repeated repairs, or a unit over 15 years old — see our furnace repair page → for the full repair-vs-replace breakdown.
Do you install heat pumps instead of gas furnaces?
Yes — heat pumps are a common alternative to gas furnaces, especially for Fresno’s relatively mild winters. See our heat pump services → for full details.
Do you offer financing for furnace installation?
Yes — $0 down, 0% interest for 18 months, with same-day approval and no hard credit pull in most cases.
More ways we help Fresno homeowners
Furnace Repair →
Furnace still running but showing warning signs? See repair options first.
Heat Pump Services →
Consider an all-electric alternative to a gas furnace.
X-Ray Diagnostic Process →
See how we diagnose the real cause before recommending any upgrade.
Get your free furnace installation estimate
Real load calculation. Written quote before any work begins. $0 down financing available.