A furnace that runs almost nonstop in a cold snap is often keeping up with a house that loses heat too fast. Cold outside walls, a thin attic, and hidden air leaks make it work longer to hold the thermostat setting. Strange noises, odd smells, cool air from the vents or frequent short cycles point to the equipment instead.
Mid November is when many households in Spokane, Spokane Valley and Coeur d'Alene first hear the furnace kick on and stay on. The nights drop well below freezing, the days stay short, and an older home on the South Hill or in Hillyard starts showing every weak spot it has.
Before you price a new furnace, it is worth a few minutes to figure out which side of the problem you are on. Here is how to tell.
Why does a furnace run longer when the house is the problem?
Your furnace has one job: replace the heat your house loses. When heat leaves through the walls, ceiling, and gaps faster than the furnace can put it back, the burner stays lit longer to catch up. On the coldest nights, it may barely shut off at all.
Think of it like filling a bucket with a hole in it. A bigger faucet helps for a while, but the water keeps draining. Patching the hole means the faucet you already have can fill it with less effort.
That is why a perfectly healthy furnace can seem to struggle in an older home. The equipment is doing exactly what it was built to do. The house is simply asking for more heat than it should.
How cold does it really get here, and why does that matter?
Spokane County and Kootenai County sit in Climate Zone 5 on the U.S. Department of Energy map, a zone known for long, cold winters. The National Weather Service puts normal annual heating degree days at Spokane Airport at 6,463, a measure of how much heating a typical year demands.
In practical terms, your furnace in North Spokane or Post Falls works for months, not weeks. A small heat leak that would barely register in a mild climate adds up over a heating season that starts in fall and runs well into spring.
Older homes feel this most. Many houses built before 1980 went up with little or nothing in the exterior walls and only a few inches in the attic. ENERGY STAR estimates that 9 out of 10 homes in the U.S. are under-insulated, so if your house is decades old, the odds are it falls short somewhere.
What are the 6 signs the problem is the house?
None of these signs proves anything alone. If three or four of them sound familiar, though, the house deserves a close look before the furnace takes the blame.
1. The furnace runs long but the air from the vents feels warm
Put your hand over a supply register while the heat is on. If the air is clearly warm and the furnace still runs and runs, the equipment is producing heat. The house is letting it go.
2. Some rooms stay cold no matter how high you set the thermostat
Corner bedrooms, rooms over a garage and rooms with two or three outside walls are classic trouble spots. If turning up the thermostat makes the warm rooms warmer and the cold rooms barely change, the cold rooms are losing heat through their walls and ceiling.
3. Outside walls feel cold to the touch
On a cold morning, press your palm flat on an exterior wall, then on an interior wall. A big difference means heat is moving straight through. A cold wall also pulls warmth from your body, which is why you can feel chilly sitting next to it even when the air reads seventy.
4. You feel drafts at outlets, baseboards or the attic hatch
Air leaks are easy to miss because they hide in plain sight. Hold the back of your hand near outlet covers on outside walls, along baseboards and around the attic access on a windy day. Moving air means outside air is getting in and warm air is getting out.
5. The upstairs is warm while the downstairs is cold
Warm air rises. In a leaky house, it escapes through gaps in the top floor ceiling, such as around recessed lights, plumbing stacks, chimney chases and the attic hatch. Cold air gets pulled in down low to replace it. This stack effect makes the furnace work harder and leaves the lower floor chilly.
6. Snow melts off your roof faster than your neighbors'
After a fresh snowfall, look at the roofs on your street. If yours clears first, or melts in patches while the house next door stays white, warm air from your living space may be leaking into the attic and heating the roof deck. It is a hint worth checking, especially when other signs line up.
When should you call an HVAC pro first?
To be fair to your furnace, sometimes it really is the equipment. A good heating contractor is the right call when you notice any of these.
- Cool or lukewarm air from the vents while the system is running.
- Short cycling, where the furnace turns on and off every few minutes instead of running steady cycles.
- New noises such as banging, squealing, grinding or rattling.
- Unusual smells, especially anything like gas or burning. If you smell gas, leave the house and call your gas utility right away.
- A dirty filter or one you cannot remember changing. A clogged filter chokes airflow and makes any furnace run poorly.
- An aging system that has not been serviced in a long time.
Ducts are worth a mention too. ENERGY STAR says about 20% to 30% of the air moving through a typical duct system is lost to leaks, holes and poorly connected ducts. If your ducts run through an attic, garage or other unheated space, ask an HVAC pro to check them.
Plenty of homes have a little of both. A tune-up and a fresh filter can help the furnace, and insulation and air sealing can help the house. Fixing only one side leaves part of the problem in place.
Is it the house or the furnace? A side-by-side look
Here is a quick way to sort the most common symptoms.
- Air from the vents: House problem, warm air but the furnace still runs long. Equipment problem, air feels cool or barely warm.
- How the furnace cycles: House problem, long steady runs on cold days. Equipment problem, quick on and off cycles every few minutes.
- Where you feel it: House problem, certain rooms or outside walls stay cold. Equipment problem, the whole house struggles at once.
- Sounds and smells: House problem, the furnace sounds normal. Equipment problem, new noises or odd smells.
- Drafts: House problem, moving air at outlets, baseboards and the attic hatch. Equipment problem, drafts are not part of the picture.
- When it started: House problem, it has always been this way and gets worse in cold snaps. Equipment problem, it changed suddenly.
Takeaway: warm air plus long run times usually means the house is leaking heat, while cool air, short cycles or new noises mean call an HVAC pro.
What happens if you replace the furnace but not the house?
A new, efficient furnace can lower the cost of each unit of heat it makes. It cannot stop that heat from walking out through empty walls or a thin attic. The cold bedroom stays cold, and the drafts by the sliding door are still there.
Sizing matters too. When a heating contractor sizes new equipment, the heat loss of the house is part of the math. A leaky house can push toward bigger equipment than a tighter one would need. That is one reason some homeowners look at insulation and air sealing before or alongside a furnace replacement, then share the results with their HVAC contractor.
If your furnace is truly failing, replace it. If it still runs well and the house is the weak link, the house is usually the better place to start.
Where does a house usually lose the most heat?
In most older Inland Northwest homes, the big three are the attic, the exterior walls and air leaks.
- The attic. ENERGY STAR recommends R-60 for an uninsulated attic in our climate zone, or R-49 when adding to 3 to 4 inches already there. Many older attics in neighborhoods like Shadle, Garland or Coeur d'Alene's Fort Grounds have far less, and what is there may have settled. Blown-In Attic Insulation brings the depth back up.
- The walls. Exterior walls in many pre-1980 homes are empty or only partly filled. Premium Injection Wall Foam goes in from the outside through small access holes, which are plugged and patched afterward, so your interior drywall or plaster stays in place.
- Air leaks. Gaps around wiring, plumbing, top plates and the attic hatch let warm air escape into the attic. Attic Air Sealing closes those bypasses before new insulation goes on top.
For larger projects, the Ultimate Home Comfort approach looks at walls, attic and air leaks together. ENERGY STAR estimates homeowners can save an average of 15% on heating and cooling costs by air sealing and adding insulation in attics, floors over crawl spaces and accessible basement rim joists. That is an average across many homes, and your results depend on your house and habits.
The bottom line
A furnace that runs long on cold nights is often doing its job in a house that leaks heat, and fixing the house can take the pressure off the equipment you already have. If the signs point to the furnace, call an HVAC pro. If they point to the house, or you are not sure, schedule a free insulation inspection with USA Insulation of Spokane-CDA before you replace equipment, and we will measure your walls and attic, take photos and give you a written price.
