Here are the most common questions about furnace replacements to CMHC staff from Canadians, and our usual answers:

Should I switch my heating fuel?

In most parts of Canada, it will be more expensive to heat with an electric furnace than one using oil or gas. An exception would be if you heat primarily with a wood stove and use the furnace only infrequently as backup. In this case, the low cost and low maintenance requirements of an electric furnace may be a major advantage. Deciding between oil and gas furnaces is a matter of choice. Make the calculation to see if it is significantly cheaper to use one fuel or another based on current prices in your area. Oil furnaces require a tank and usually a chimney. There may be additional costs for chimney modification or oil storage tanks when purchasing an oil furnace. Some home insurance companies require periodic oil tank replacements. Check if a new gas furnace would also require relining the chimney. Consult with your contractor and make sure that these costs are included in your estimates.

Some dealers recommend a furnace of 100,000 Btu/h, and some say 80,000 Btu/h will be fine. How do I choose?

See the previous discussion on sizing. If you are buying an oil furnace, proper sizing will affect the durability and efficient operation of your appliance. Your choices are either to pay for a proper heat loss analysis, to calculate house heat loss or to accept the dealer's estimate. Sometimes government or utility programs subsidize house testing. If such a program is in effect in your vicinity, this can be an economical way to have your house heating load established.

Are there any advantages to multi-stage, multi-speed furnaces?

Multi-stage furnaces have become more popular lately, although they are more expensive than the single stage furnaces that have been sold for decades. Multi-stage furnaces have two or three levels of burner function, and an efficient, modulating circulation fan to move the heat into the house. They can provide additional heat when a quick temperature rise is required, such as in the morning when a house with a setback thermostat is being heated from 15°C to 21°C (59°F to70°F). A traditional single speed furnace would take longer to get up to temperature. The multi-stage furnaces are no more efficient than single-stage furnaces; they offer more flexibility and perhaps more comfort.

Is Furnace "A" better than Furnace "B"? How can I find that out?

There is little or no available data to show that one manufacturer's furnace will operate longer and with less trouble than a furnace from another manufacturer. This is frustrating for consumers. We are used to being able to read ratings of one product versus another product and to make a choice based on those ratings. However, a good furnace will last 25 years. A poor one may break down prematurely at 15 years. With lifetimes of this length, and with furnace design and model changes, it is hard to predict which furnace will provide the best service.

There are two factors to help you in your choice. Pick a furnace with a long heat exchanger warranty, 20 years or more. If manufacturers are willing to back the most expensive part of their appliance for a long time, this should inspire some confidence. Also, pick a furnace manufacturer and a dealer that have been in business for a significant period of time. A furnace with a lifetime warranty offered by a company that has been in operation for only three years may not be the best deal. One would expect to pay less for this level of uncertainty. Look for contractors with memberships in trade organizations such as HRAI, which would indicate an interest in professional qualifications.

The Hot Water Heater Conundrum

There are very few high-efficiency hot water heaters available. Changing your furnace may lead to having to think about your hot water heater. Existing hot water heaters are often located vertically below the kitchen and bathrooms, where the water is used. If you are changing from an electric to a conventional gas hot water tank, and the new gas appliance has to be installed across the basement to be near the chimney, you will be waiting longer for the hot water at the tap. Consider a gas hot water tank that has side-wall venting and does not require a chimney. This way, it can stay close to the plumbing appliances that use it.

Another hot water tank issue can occur when you switch from a conventional gas furnace and hot water tank to a new, high-efficiency side-wall vented furnace. Now the hot water tank has to heat up that big chimney all by itself, and you probably will have to pay for chimney relining. It is often better, when choosing a chimneyless furnace, to switch your hot water tank to side-wall venting at the same time and seal the old chimney closed. However, side-wall vented hot water heaters are more expensive than conventional hot water heaters and can be noisier.

Instantaneous hot water heaters, which do not use a storage tank, are becoming more common. They may be more economical to operate.

Furnace Circulating Fan Choices

Most furnace circulating fans consume high amounts of electricity (300 – 700 watts). If you will be using your furnace circulating fan to move ventilation air around the house (for instance, if you have a heat recovery ventilator connected to it, or a high-efficiency air cleaner on the furnace), then look at upgrading the circulating fan to a high-efficiency DC motor. The best furnace fans now will use less than 100 W on low speed. This will result in considerable electrical savings over the life of the furnace.

Other Choices

When replacing the furnace, you may want to look at integrated systems that heat your house and your water and also provide ventilation. Devices known as "combo" units provide house and water heating. New appliances with advanced, integrated systems will provide ventilation as well as space and water heating. For some replacements, these integrated appliances will be your best choice.