That question has a real answer, and it is not a feeling about how tired the furnace looks. Four things settle it, and you can check three of them yourself before anyone comes out: how old the furnace actually is, which part failed, how many times this same unit has already been down, and what a newer one would and would not change on your gas bill. This page works through them in the order homeowners ask them.
One thing first. If the heat is off in your house right this minute, this is the wrong page to be reading. Call, and we will settle the decision standing in front of the unit instead of in a browser tab. Our furnace repair page covers what that visit looks like. Everything below is for the other situation: the furnace still runs, or a repair quote is sitting on the kitchen counter, and you have room to think about it.
How old is my furnace, and where do I find that out?
This decision starts with a number that is already written down in your basement, and it is worth reading rather than estimating.
Open the front door of the furnace, or look along the side of the cabinet. The rating plate is a metal or foil label carrying the brand, the model number, the serial number, the BTU input, and on some units the manufacture date spelled out in plain text. Where the date is not spelled out, the serial number encodes it, and the scheme belongs to the manufacturer. One brand puts a week-and-year pair at the front of the serial. Another buries a single letter that stands in for the year. It is a lookup against that brand's own key, not a guess, and it takes about a minute once somebody can read the plate.
Photograph the whole plate with your phone while you are down there, brand and model and serial in one frame. That photo is the difference between a phone call where parts can be looked up before the truck is loaded and one where they cannot.
Two other things in that same spot are worth a look. Service companies leave dated stickers on the side of the cabinet, and a stack of them is your furnace's repair history written down by whoever was here before us. It answers the how-often-has-this-broken question better than memory does. And the year you bought the house is not the year the furnace went in. Read the plate. Do not date the furnace to the closing.
Is my furnace too old to repair?
Age on its own decides almost nothing. It sets the stakes; the failed part and the breakdown history make the call.
Here is how we band it. These bands are our own decision rule, not a statistic and not a number off a manufacturer's brochure.
Under ten years. We fix it, then work out why it failed this early. A furnace that dies young is pointing at something outside the cabinet: airflow, a filter nobody changed, or a unit that was never sized for the house in the first place.
Ten to fifteen. The failed part and the repair history decide it. A small part is still just a small part.
Fifteen to twenty. A gas furnace is living out the normal end of its service life in this band. A minor repair is still worth buying. But once the repair in front of you costs anywhere near half of what a new system would run, replacement is the better math. You stop paying for today's failure and start buying years back.
Past twenty. Every repair is life support, and we would rather say that plainly than quietly sell you the part.
Electric furnaces sit at the forgiving end of all four bands. There is no combustion section in one, so nothing is corroding from the inside.
Run those bands against real examples and you can see why the calendar cannot answer this by itself. A nineteen-year-old furnace with a dead igniter and no other history gets an igniter. A twelve-year-old furnace with a cracked heat exchanger gets replaced. Put a failed blower motor on that same nineteen-year-old unit, on top of two other breakdowns since November, and the answer flips again.
Which furnace repairs are worth paying for?
Furnace parts sort into classes, and the class matters more than the year on the plate.
Controls and consumables. Hot surface igniter, flame sensor, thermostat, run capacitor, pressure switch, high-limit switch, transformer, control board, gas valve, and on electric units the sequencers and the heating elements themselves. These are ordinary catalog parts, the common ones ride on the truck, and replacing one is a repair at almost any age, because none of them costs anything close to half a new system. A nineteen-year-old furnace with a bad igniter is a furnace with a bad igniter. It is not a furnace at the end of its life.
Major mechanical. The blower motor and wheel, and the draft inducer assembly. These are still repairs, and on a younger system they are obvious ones. But short of the heat exchanger these are the most expensive components in the cabinet, and this is the class where the half-the-price test actually gets tripped on an older unit. This is the repair that deserves a replacement number written next to it before you say yes.
Two situations quietly turn a fixable part into an unfixable one. Either the part is discontinued and no supply house in the valley has one on a shelf, which in the middle of January is a decision all by itself. Or the failure is the third one this season in a third different section of the furnace. An igniter in November, an inducer motor in December and a control board in February is not three problems. It is one system wearing out all at once, and the next part is already on its way.
Which furnace problems mean it is time to replace it?
Some failures end the debate, and the biggest one is not economic at all.
A cracked or corroded heat exchanger. The heat exchanger is the steel that keeps combustion gases on one side and the air your family breathes on the other. A breach in it is a carbon monoxide problem, not a repair line item. We do not patch them. We shut the unit down when we find one, and the answer is replacement regardless of what the calendar says.
Because that verdict is an expensive one to be handed, it is worth knowing what an honest inspection looks like. The burners come out. The cells get looked at directly, with a mirror and with an inspection camera fed down through the burner ports, because a cell can crack along the top bend where nothing shows from the front of the cabinet. Two field checks back up what the camera sees. The flames first: burner flames that lift off, roll out toward the front, or change shape the instant the blower starts are air crossing where it should not be. Then the numbers: a combustion analyzer in the flue while carbon monoxide is measured in the air coming out of a supply register. Rust flakes and scale sitting in the burner compartment, and heavy corrosion under the inducer, are the other tells.
When we condemn a heat exchanger you get shown the photograph and the readings, not handed a verdict. And if anyone tells you a heat exchanger is cracked without having opened the burner compartment, get a second opinion before you buy a furnace.
Old install problems there is no fixing around. Sometimes the furnace is not really what is wrong. The venting is wrong, the gas line is undersized, or the clearances were never right, and none of it can be corrected without pulling the cabinet out. A burner assembly rusted through lands in the same place.
Is it cheaper to repair or replace a furnace?
You have probably run into the rule that says replace it once a repair costs a big fraction of a new system. It is a real rule and we use it: past fifteen years, a repair approaching half the price of a new system is the point where replacement becomes the better math. Our furnace installation page states it the same way, because it is one rule, not two.
What that rule cannot tell you on its own is how much furnace you have left, and that is the figure that finishes the decision. Think in cost per remaining year of service. The identical repair is a very different purchase on a furnace with eight good years in it than on one with two, and nothing you can do over the phone tells those two apart. That is the entire reason the assessment happens at the unit.
Three things move the arithmetic that are easy to leave out. The efficiency gap, which shows up on every gas bill from November through March. The condition of your ductwork and return, which decides how much of the heat you pay for actually arrives in the rooms. And the air conditioning coil sitting in the plenum above the furnace, which gets a say in this whether you want it to or not.
Will a new furnace actually lower my gas bill?
Some. How much is something you can work out for your own house rather than take off a brochure.
Furnace efficiency is a percentage called AFUE: the share of the gas you buy that ends up as heat in the house instead of leaving through the flue. Your existing furnace's number comes from the model number you photographed. The new one's is on the quote. Divide the old number by the new one. That fraction is roughly how much heating fuel you would still be buying for the same warmth in the same house, and the remainder is what stops going up the chimney.
Now the part a sales sheet leaves out. That reduction applies to the heating share of your bill, not the whole bill, and only during the months you are actually heating. The water heater, the range and the dryer are on that same gas bill and nothing about them changes.
So measure the heating share yourself before you weigh a tier. Pull twelve months of gas bills. A summer month is close to your non-heating baseline. Subtract that baseline from each winter month, and what is left is what heating actually cost you last year. Apply the efficiency fraction to that number, not to the total, and you have an estimate built out of your own house.
Two practical notes before assuming higher is automatically better. A high-efficiency condensing furnace does not vent up the old metal flue. It vents in PVC out through a wall or the roof, and it makes condensate that needs a drain and often a pump. And if your old furnace shared a masonry chimney with your water heater, taking the furnace off that chimney leaves the water heater venting alone into a flue far too large for it, which puts a liner on the job. Neither of those is a reason to avoid a condensing furnace. They are the reason the installed cost is not just the price of the equipment, and the reason you want the whole thing on paper before you pick a tier.
Do I have to replace my air conditioner at the same time?
Not necessarily. But decide it on purpose rather than by default.
If your home has central air, the evaporator coil sits in the supply plenum directly above the furnace. It comes out when the furnace comes out, because the sheet metal it lives in is what the new furnace has to connect to. If that coil is the same age as the furnace, replacement day is the one day it is inexpensive to deal with, because the labor is already happening. Pairing a brand-new furnace with a worn-out coil is a compromise that shows up in July rather than in January, which is exactly why it is easy to skip when you are making this decision in the cold.
My furnace died in January. Do I have to decide tonight?
No. You should not have to choose between being warm tonight and making the right call in the morning.
When a furnace fails mid-season and replacement is clearly the answer, the practical question is what carries the house until equipment is in. Sometimes a temporary repair does that, and it is money well spent. Sometimes it is money you will not get back, and we would rather tell you that before you spend it than after. Either way, furnace-out calls go ahead of routine work on our schedule.
The clock that matters is the equipment, not the labor. A straightforward like-for-like replacement is a one-day job: the crew arrives in the morning and you have heat that night. About two-thirds of the furnace and HVAC system installations we have completed since 2023 were finished the same day they were scheduled. What stretches a job past one day is a change of some kind, and it is nearly always one of four. Moving from a standard-efficiency furnace to a condensing one, with the new venting and condensate that come with it. A return duct that was already marginal behind the old blower and will not do behind a new one. Access, meaning an attic, a tight crawl space, or a closet with a door narrower than the new cabinet. Or an electrical circuit and disconnect that have to be brought up to current code. Ordering runs on its own separate clock, and a specific efficiency tier or an odd cabinet width can add days before we can start at all. You should walk away from the estimate visit knowing both dates.
The mechanical permit and the inspection are part of the job and we handle them. The inspection happens after the install, without taking your heat back offline.
What does it cost to replace a furnace?
There is no price on this page, and that is deliberate. Nobody can quote a furnace replacement from a phone call. A company that hands you one is quoting a house it has not seen.
Here is what that number is actually made of: the heating capacity your house needs, which comes from square footage, insulation and window area rather than from copying the BTU rating off the old plate; the efficiency tier you choose; gas or electric; whether the venting has to change; the condition of the ductwork and the return; condensate and electrical work; the permit; whether the coil is being handled at the same time; and how hard the space is to work in.
So we do it the other way around. A technician comes to the house, looks at the actual system, and puts the repair option and the replacement option side by side in writing. That visit is free, and there is no obligation to take either option. Then you decide using real numbers for your house instead of averages for somebody else's.
Who can look at my furnace and give me a straight answer?
Since 2023 our crews have completed more than 850 heating and cooling estimate visits and more than 400 furnace and HVAC system installations across the Treasure Valley and eastern Oregon. Which is a long way of saying we have had this exact conversation in a lot of basements and hallway closets, and that the answer is not always a new furnace.
American Heating & Air is the HVAC division of American Rooter & Drain, licensed and insured in Idaho under HVAC Contractor License LIC# 029771, working out of the shop on Commercial Way in Caldwell and serving the greater Treasure Valley since 1945.
If you already know you are replacing it, furnace installation covers sizing and equipment, and heat pumps are worth a look if you are weighing heating and cooling together. If the furnace is still running and you would like to keep this decision a few years away, an annual furnace tune-up is the cheapest thing named on this page. You can also see what we cover near you in Boise and near you in Payette.
Call (208) 366-5771 and a real person picks up.
