When to Replace a Furnace
Repair or replace? The clear signs it's time for a new furnace: age, a cracked heat exchanger, repeated repairs, bills and safety.
Furnace Installation services
Each guide below covers one specific winter problem: symptoms, causes, what you can safely check and what a licensed technician does. Prices are explained in the furnace installation cost guide.
High-Efficiency Furnace Installation
Compare 80% and 95%+ AFUE furnaces: venting, condensate, single-stage vs modulating, and which makes sense for your climate.
Furnace Sizing (Manual J)
Why square-footage rules of thumb oversize furnaces, how a Manual J load calculation works, and the comfort problems a wrong-size furnace causes.
Dual-Fuel Heat Pump + Furnace
How dual-fuel systems pair a heat pump with a furnace, the balance point, who benefits most and what installation involves.
Emergency Winter Furnace Replacement
Furnace died mid-winter and can't be repaired? How emergency replacement works, temporary heat, timelines and how to avoid a rushed decision.
Common winter problems and where to start
| Problem | What usually causes it |
|---|---|
| Not sure it's time to replace | Age, repairs, safety and bills all count. When to replace. |
| 80% or 95%+ efficiency? | Climate, venting and fuel prices decide it. High-efficiency furnaces. |
| What size do I need? | Bigger isn't better. Furnace sizing. |
| Considering a heat pump too | Dual fuel combines both. Dual-fuel systems. |
| Emergency replacement in winter | What to expect when the old furnace can't be saved. Winter replacement. |
Watch: winter heating explained
Short, silent clips hosted on muse.ai that show what to look for. They play muted and loop.
Coverage map: all 50 states and DC
Pick your state for local winter conditions, common heating fuels and the cities we route calls from. Colors show how severe winters are, based on IECC climate zones.
- Severe cold (IECC 6–8)
- Cold (5)
- Mixed (4)
- Mild (1–3)
How it works
- Call and tell us about your home, current system and timeline.
- We connect you with a licensed installer serving your area.
- The installer evaluates the home, sizes the furnace and reviews venting, gas and duct needs.
- You receive written options and pricing before deciding.
- Installation, permit and inspection where required, start-up and a combustion check.
Decision guide
| Factor | 80% AFUE furnace | 95%+ AFUE condensing furnace |
|---|---|---|
| Fuel used for heat | About 80% of fuel becomes heat | 95% or more becomes heat |
| Venting | Metal flue, often into a chimney | PVC pipes through a wall or roof |
| Condensate drain | No | Yes; needs freeze protection |
| Best fit | Mild climates, some attic installs | Cold climates with long heating seasons |
| Learn more | Compare in detail | Sizing guide |
Before you call
Have the equipment type, brand and any blinking error code ready, and note what you've already checked. If anyone at home smells gas or a CO alarm sounds, leave the house and call 911 or the gas utility first.
Keystone Comfort Furnace Installation is a referral service. Your call is connected to an independent, licensed provider who serves your ZIP code and quotes the job directly. How it works.
Furnace Installation questions, answered
How long does furnace installation take?
A straightforward replacement often takes one day. Changing from 80% to 95%+ efficiency, new venting, duct modifications, or moving the furnace can add a day or more.
How long do furnaces last?
Gas furnaces commonly last about 15–20 years, sometimes longer with good maintenance. Age alone isn't a reason to replace, but it matters when a major repair comes up.
What size furnace do I need?
It depends on your home's heat loss, not just square footage. Installers should use a Manual J load calculation, which accounts for insulation, windows, air leakage and your local design temperature.
Is a 95% AFUE furnace worth it?
In cold climates with long heating seasons it usually pays back faster. In mild climates the savings are smaller, and the venting cost may tip the balance toward 80%.
Do I need a permit to replace a furnace?
Most US jurisdictions require a mechanical permit, and often a gas permit, for furnace replacement. A licensed installer typically pulls the permit. Requirements vary by city and county.
Are there tax credits for a new furnace?
The federal 25C energy-efficiency tax credit ended for equipment placed in service after December 31, 2025. Check your utility and state energy office for current rebates.