Keep running the old gravity furnace or finally upgrade?

I had the same setup in my 1912 foursquare in Cleveland, an old American Radiator gravity unit that came with the house. I babied it along for years because it never broke, but when I finally sat down with two winters of gas bills and compared them to what neighbors with modern furnaces were paying, the difference was too big to ignore. That old thing was probaly converting half the gas I bought into actual heat, and the rest went up the chimney flue that ran through the middle of my house.

I put in a Carrier two-stage furnace in 2019 and my January gas bill dropped from around $190 to about $95, same thermostat habits, similar winter. The install was about $9k because the returns had to be redone, but the savings put the payback somewhere around 10 years, longer than I initially guessed. So the math is real but slower than the sales pitch suggests.

Two things nobody warns you about though. The new blower moves air constantly and my house is dustier now, and the heat feels diferent, less of that slow warm soak from the big registers. On the upside I got a whole corner of my basement back where the monster used to sit. If your bills are tolerable and the chimney and heat exchanger check out, there is no shame in riding the old girl a few more years while you save up.

I'm in the middle of this exact debate but leaning the other way. My 1930s colonial in Providence still runs its original gravity furnace, and instead of replacing it I spent two falls sealing up the house itself. Weatherstripped every one of those old double-hung windows, blew cellulose into the attic, and had someone air-seal the rim joist in the basement. My gas usage dropped noticeably the following winter without touching the furnace at all.

The way I figure it, an old gravity system loses heat up the stack, sure, but alot of the waste in houses like ours is warm air leaking out of the building, not the furnace itself. The previous poster compared bills with neighbors, but unless those neighbors live in identical houses with identical insulation, that comparison mixes two variables togehter. Here's what sold me on keeping mine: when the blower motor died in my sister's modern furnace a few Januarys back, she was without heat for three days waiting on a part. Mine has no blower to die. When it eventually does need replacing, I can do the full swap then, and every dollar I spent on insulation carries over to whatever heats the place next.

One practical tip if you keep yours: have a pro check the heat exchanger and the chimney lining. Old gravity units run cool flue gases and those clay tile liners crack over the decades.

My aunt has one of these in her old house in Queens and I always loved how the floors above it stay warm in the winter, no fan noise at all. I keep wondering though, coud you just stick some kind of small fan in the big ducts to push the air around better instead of ripping the whole thing out? Or does that defeat the point of the old design?

My old man converted the same kind of coal monster to gas back in the 60s and it ran another 40 years before we finally let it go. One thing that helped us stretch it out was having the gas company out every few years for a free check on the draft and the heat exchanger. They'd catch rust-through before it became a problem. That old chimney ran up the middle of the house and gave off heat everywhere, which is half the reason the place felt warm even when the burners cycled off.

I'd take that Cleveland comparison with a grain of salt. Comparing your gas bill to your neighbors' doesn't tell you much about the furnace when thier houses are different sizes, different insulation, different thermostat habits. Your own before and after bills are the only numbers that count, and even those are shaky if gas prices moved between the two winters. Did you adjust for what a therm actualy cost each year? Also curious wheather you factored in that a two-stage blower draws power all winter, wich never shows up on the gas bill but sure shows up on the electric one.

Rode mine for years before I touched anything, and honestly the ducts were the weak spot, not the furnace. Those garbage-can sized runs in my basement ran through an unheated corner and the first floor got warm air while the upstairs registers barely breathed. I wrapped the accessible runs with foil-faced fiberglass duct wrap one weekend and the bedrooms heated noticeably faster that winter. Same gas burned, more of it landing where we actually sit. Didn't fix the efficiency problem, but if you're keeping the old girl a while, the wrap was the single best forty bucks I spent on that system.