How to Assess Your Furnace for Replacement

A repairman working on a furnace.

Most furnaces last anywhere from 16 to 20 years, and there are tell-tale signs when it comes time to replace it. You have many things to consider when buying a new furnace, so consider all your options. The fuel source, energy efficiency, and size of the new furnace are all things to consider. Keep these in mind and the process should be a breeze.

Tell-tale Signs

First do a visual check around the furnace itself for obvious signs that it needs replacing. Check for rust or corrosion either on the inside or on the outside of the furnace. Are there any cracks? Take a look at the flame—is it a steady blue flame with no gaps? A yellow flame suggests that the furnace is not burning the fuel correctly.

How often does the furnace turn off and on? If it seems to be cycling more than usual, you might only have to change the filter. If that doesn’t work, have it inspected by a professional you trust.

How does the furnace sound? If it is becoming noisier than usual, have it checked. If your furnace is the right size for your home, you should barely notice when it is on.

Following are some telltale signs that aren't obvious on the furnace itself. Does one room seem to always be colder or warmer than the rest of the house? If your furnace and ducts are the right size, then all rooms should be very close to the same temperature. Do you seem to be dusting the furniture more often? When a furnace is starting to work, it will put out more dust and possibly rust particles. Energy bills are always going up but check your bill and see if it is going up for other reasons. If the usage is the same, but your bill keeps rising, there may be a problem with the furnace itself.

Types of Fuel Sources

The three most common fuel sources are natural gas, propane gas, and electric heat. However, there are also many older furnaces that still use fuel oil. You can get fuel oil furnaces to replace an old one, but they are becoming harder and harder to find.

Historically, natural gas has been the least expensive way to heat your home. Of course, the costs vary depending on the climate in which you live. An electric furnace, however, will more than triple your heating bill as compared to natural gas. If the gas bill for heating your home in a winter season is $2,000, the electric bill for the same amount of time and usage would cost closer to $5,000. Propane gas in the same scenario would be about $3200 and fuel oil about $2300.

Based on these estimates, it's easy to see that natural gas would be the way to go, if it's available in your area. (Natural gas is the cleanest fuel source as well.)

The Best Time to Replace

If you live in a climate where there are four seasons, the best time to replace your furnace would be in early spring or early fall. The demand for heating contractors is usually pretty low during these times and therefore you might get a break on the installation charges.

Also, if you are thinking about buying a house, the furnace is one thing you want checked thoroughly before you make any commitments. Furnace replacements can cost anywhere from $2,500 to $14,000 depending on your locale, the type of furnace, and if any reducting needs to be done.

Costs and Estimates

One of the biggest reasons costs can vary for a furnace between $2,500 and $14,000 is because the current furnace may have been too big or too small for your size of home. You may need a bigger furnace, which would require many changes to your current system, including replacing duct work. A furnace is much more efficient if it is the correct size for your home. If it is too big, it will cycle on and off too often, which reduces its efficiency. If it is too small, it will be overworked and need replacing sooner than normal.

Don’t be fooled by the cost of the furnace. Remember that you will be using that furnace for (potentially) the next 20 years, so you will want to factor in the cost of the fuel as well. For instance, the average cost for a new gas furnace is $2300, but a new electric furnace is only around $1900. Even though you pay more up front for the gas furnace, you will save in fuel costs in the long haul.

You should get at least three estimates from local installers. Try not to use the internet to locate an installer as there are many horror stories about fly-by-night installers that take your money and run. Use word of mouth.

While you have the installer on the phone, ask if they can do a heat load calculation on your home. (Any qualified HVAC installer will know what you are talking about.) Heat load, simply defined, is the amount of heat units it would take to keep the temperature in a building at a specified level. Your contractor should know how to calculate the heat load. If he doesn’t, get someone else.

During the inspection, keep an eye on the contractor. He should be checking any areas that could cause heat loss, such as windows, walls (including basement walls), and leaky duct work. He should also be taking into account how many doors you have, if your roof is letting any heat escape, and how many rooms are carpeted as opposed to bare. All these components should go into the installer’s heat load calculation because they are all part of how hard your furnace will have to work.

After all is said and done, the installer should have a pretty good idea of how large a furnace your house will need.