If you’re replacing a gravity furnace, you can expect to pay between $4,500 and $11,000. Gravity furnaces are no longer installed, so replacement is usually recommended.
An older home might have an older heating system–like a gravity furnace–and replacing it wouldn’t be out of the ordinary. A gravity furnace uses (you guessed it) gravity to heat a home. If you’ve ever seen a mess of ventilation pipes leading to a large furnace in a basement, then you’ve seen a gravity furnace. While they are no longer installed, gravity furnaces used to be the pinnacle of efficiency. If you find one in your home, or if there’s one in a home you’re thinking about purchasing, you need to know how much it will cost to replace it, or if it’s a better idea to replace or convert it.
Replacing a gravity furnace isn’t cheap. Not only are new furnaces thousands of dollars, but the removal of the old “octopus” furnace involves hours of labor. If there are any signs of asbestos in the furnace or ductwork, expect your cost—and the labor required—to increase significantly.
Labor runs between $75 and $100 per hour for furnace work, and that is only for a straightforward job. If there is asbestos present, or you need new ductwork, that cost can increase significantly as asbestos requires professional removal, and some companies won’t do large duct jobs. Removing and replacing a furnace can take anywhere from 6 to 12 hours.
| Hours Worked | Total Labor Cost |
|---|---|
| 6 hours | $450 – $600 |
| 12 hours | $900 – $1,200 |
| 18 hours | $1,350 – $1,800 |
At least half of the labor cost will go toward removing the old furnace. Let’s assume there is no asbestos present. The minimum amount of prep work you will need to do includes:
Ensuring there is a safe and clear pathway to remove the old furnace.
Arranging for pickup or finding a metal scrap facility, if you’re DIY the removal.
Ensuring your new furnace is up to code. A pro can do this for you.
Shutting off all utilities.
Disconnecting the old furnace.
Inspecting all the ductwork. A pro might do this with a camera.
Once you’ve completed the prep work, you need to ensure you have all the tools to perform the removal. Removing an old furnace usually requires a screwdriver, crowbar, dolly, and some friends to help with the heavy lifting. You may also need a metal saw.
Once the gravity furnace is removed, it’s time to swap it for a different heater. Each type of furnace has its advantages and disadvantages—which one you choose will come down to your budget, available hookups, and preference.
| Furnace Types | Average Unit Cost (plus install) |
|---|---|
| Natural Gas | $3,800 – $10,000 |
| Electric | $2,000 – $7,000 |
| Oil | $6,750 – $10,000 |
| Propane | $3,700 – $14,200 |
A natural gas furnace is extremely efficient and is the most common type of furnace found in modern homes. It may have a higher initial cost, but since natural gas is ridiculously inexpensive, it could save you money over time. Because it is so efficient, it doesn’t need to run as long as other furnace types—another benefit is lower electricity costs.
An electric furnace is often found in homes where natural gas may not be an option. It requires a lot of electricity to run an electric furnace, so it isn’t the first choice for those who are conscious of their bills. An electric furnace is usually found in homes located where the winter is mild, and the heating system doesn’t need to be robust. It heats slowly, but requires very little maintenance and while it costs less than a gas furnace to purchase and install, you can expect a higher monthly electric bill.
Considered safer than a gas furnace, an oil furnace requires more maintenance and the oil can be quite expensive. As far as efficiency, this furnace is somewhere between a natural gas and electric furnace. An oil furnace creates carbon monoxide, and is less environmentally conscious than the other furnace types.
Not as commonly seen as the other types on this list, a propane furnace can either be installed above or below the ground. It’s not too efficient, and can cost a lot to install. However, some houses can last an entire winter on one large tank of propane, thus limiting their heating bill for the entire season to around $800.
Gravity furnaces are an outdated technology. Like other older appliances, there are certain quirks that need to get ironed out—even when removing such equipment–to bring it up to a modern standard. Depending on when it was installed, you might want to consider the presence of asbestos. This naturally occurring mineral can be quite dangerous when handled incorrectly.
This is probably the most extensive aspect of replacing a gravity furnace. If the ductwork contains asbestos, it’s usually recommended that the entire system is removed and replaced. While you may be able to keep the existing vent placements, removing the ducts from the walls and floors can become extremely expensive.
If removal isn’t required, modifying ductwork to bring it up to code should be significantly cheaper. Installing new ductwork will cost about $2,000 to $5,000.
This is where things get interesting (and not in a good way). Asbestos is a known carcinogen that is no longer used in new builds; however, it can still be found in older homes. There’s a chance that your gravity furnace contains asbestos, which is why we recommend that you hire a pro to inspect for asbestos. It may only be present in the furnace itself but, more often than not, it’s used throughout the entire system, which will require a total removal.
If it were a modern furnace, you could remove and replace it yourself. It would require some strength and time, but it’s a doable job. The issue with a gravity furnace is that because they’re old tech, they often weigh a literal ton and may contain materials that can be hazardous to your health, and to the health of your household.
For these reasons, we strongly recommend hiring a professional to remove and replace the unit and, if necessary, the ductwork. If the unit (and the ductwork) is free of dangerous chemicals, you may be permitted to work alongside the professional. If there is asbestos, or if you are unsure if it’s present, you need to hire a local asbestos removal professional for safety reasons.
There are really only a few ways you can save money when replacing a gravity furnace. The choice is usually out of your control, as it will be dictated by the condition of the existing furnace (and ductwork), and the available heating methods in place for your home.
If you do have the option of the type of furnace you install, some money-saving tips include:
Installing the furnace type that will save you the most money over time, as furnaces seldom need replacing.
Discussing fuel options with multiple providers.
Repurposing and reusing the existing ductwork, if there is no asbestos.
Purchasing a used furnace, especially if you go electric.
Installing in late spring or summer when contractors are in lower demand.
Selling your old furnace (for scrap metal).
Gravity furnaces work, and they heated houses for hundreds of years, but they aren’t very efficient and they can be expensive to run. Most of the time, a gravity furnace devalues a home, and is replaced with a more modern system when an older home is sold. There really aren’t many benefits to keeping a gravity furnace. The only real reason you would keep it is due to the expense of replacing it, or you enjoy its novelty.
The vast majority of gravity furnaces don’t have filters. There are a few reasons but the main reason is that gravity furnaces were built before modern filters were invented. The furnace uses hot air to move heat around (unlike forced-air systems that we use today), and filtering the hot air simply wasn’t common practice. Because of advancements in air studies, it’s known now that having an air filter in your furnace is essential to maintaining air quality when heating your home.
The short answer is no. Gravity furnaces lose a lot of heat through the ductwork, which is why the ductwork was commonly insulated with asbestos. The hot air that rises from a gravity furnace also doesn’t move as quickly as it would in a forced-air system, which means it loses heat faster due to the time it spends in the ducts. Finally, gravity furnaces simply don’t burn fuel as efficiently as modern systems.
No, but it’s common that they do. Gravity furnaces weren’t terribly efficient so wrapping either the ductwork in asbestos, the furnace itself, or both, was something done regularly. This allowed the system to retain more heat. At the time, this greatly enhanced the efficiency of the furnaces but it wasn’t until later that we became aware of just how carcinogenic and dangerous asbestos could be.
Gravity furnaces, even when wrapped in asbestos, are generally considered safe. They become much less safe if any of the asbestos is removed or damaged, as it then spreads through the system into the house. Only a professional will be able to tell you if your gravity furnace poses a danger to your health or your home. After a proper assessment, you’ll be able to decide if replacing it is worth the time and investment.
