How Much Energy Can a New Furnace Save You?
Eleven thousand dollars. A 97% efficiency rated unit, top-of-the-line, installed clean. The guy called me the following March because his gas bill had barely moved.
Turned out a trunk line had pulled loose in the crawlspace. Been heating dirt down there for who knows how long probably since before he bought the furnace, maybe since before he bought the house.
Start With What’s Already Broken
That’s the part nobody puts on a quote sheet.
Ductwork in a lot of these older houses got retrofitted decades after the place went up. Snaked around joists, elbowed through whatever gap somebody could find, patched with cloth tape that gave up sometime during the Clinton administration. You can put a perfect furnace on the other end of that and still lose a third of your energy before it reaches the register.
Sealing it costs a fraction of the equipment. Same with the attic plenty of Northfield homes have whatever got blown up there in the seventies and nothing since. Neither job is exciting. Both beat two efficiency points.
Now the Furnace Math
AFUE is the number on the yellow sticker. It’s the share of fuel that becomes heat in your house instead of warming the sky.
Most of what I pull out of basements around here reads 70 to 80. New condensing units read 95, 96.
So: $1,600 a year in gas at 70 percent means roughly $480 goes up the flue. Energy you paid for and never got. Move to 95, you keep most of it.
What makes that worth doing here is the season. October into April, and the thing runs for most of it. Same upgrade in a place where the furnace fires up for six weeks in January doesn’t pencil out the same way at all.
The Size Is Wrong More Often Than the Brand
A 96 installed badly loses to a 92 installed right. Every time.
Usually it’s oversizing. Guy reads 80,000 BTUs off the old unit, drops in another 80,000, gone by lunch. Except the old one was probably oversized too somebody made the same lazy swap in 2004. Now you’ve got a furnace that satisfies the thermostat in six minutes and shuts off, burning energy on every startup, chewing through igniters. Back bedroom’s still cold when the wind’s out of the north.
A real load calculation weighs insulation and window area against square footage. I’ve swapped 80,000 for 60,000 and had homeowners tell me the house finally feels even, which sounds backwards until you’ve watched it happen a few times.
Thermostat’s the free one, by the way. Five degrees back overnight, five more when the house is empty. Just don’t drop it fifteen and expect it caught up by breakfast.
When I Tell People Not to Buy One
Age alone isn’t a reason. Sixteen years old, lights first try, holds temperature through a cold snap, hasn’t needed a part in three winters? Leave it. Six grand against three hundred a year in energy savings is a long road back.
Flips fast, though. Cracked heat exchanger, that’s done. Second $700 repair inside one season, that’s done too. I stop quoting parts around there.
Worth knowing: a furnace replacement here needs a mechanical permit and an inspection. Licensed shops pull it without being asked and it’s already in the price. Somebody offers to skip it and knock two hundred off, you’ve just learned something about how they’re going to handle your venting.
Get Ahead of It
The worst version of this is nine at night on the coldest day of the year, no heat, taking whatever’s on the truck. Call SouthSota One Hour Heating & Air Conditioning in September and get a load calculation while you’ve still got options.
FAQs
Will a new furnace cut my bill in half?
No, and whoever told you that is selling. Seventy to 95 percent trims maybe 20 to 30 percent off the heating portion. Water heater and dryer are pulling the same energy they always did.
Is the 96 worth the extra or is that an upsell?
In Northfield, usually worth it costs more and needs PVC out a sidewall, but the winters are long enough to earn it back. Somewhere with a short season I’d tell you to keep the money.
20 years old and runs fine. Am I an idiot for keeping it?
Nope. Run it. Get the heat exchanger checked every fall that’s a safety thing, not an energy thing. And price the replacement now instead of in February when you’ve got no leverage.
how long am I without heat during install
Four to seven hours on a straight swap. Longer if we’re converting a metal flue to PVC or moving the unit. Plan on a workday. Nobody books this in January by choice.
Do I really need the ducts looked at too?
Have someone put eyes on them at minimum. Disconnected trunk lines aren’t rare in older Northfield houses, and it’s a lot easier to reach while the old furnace is out of the way.
Check the repair history before you check the efficiency sticker. That’s the order.
