You have a wide range of options when it comes to a new furnace. The type of furnace you choose can make a significant difference in your heating costs and how easily you can keep your home warm during extreme cold spells. One of the best options for lowering your heating costs and improving your comfort is a variable-speed furnace. While a variable-speed furnace isn’t necessarily the right option for every home, it’s definitely an option worth considering when your old furnace reaches the end of its lifespan.
What Are Variable-Speed Furnaces?
Most furnaces are either single-stage or two-stage units, and these terms refer to the number of power settings they have. Single-stage furnaces can only operate at full power, which typically results in them cycling on and off several times an hour. What makes two-stage furnaces different is that they have a three-way gas valve that can either be fully open or just partially open. When the valve is only partially open, the furnace runs at a lower power and produces less heat. With most two-stage units, the lower setting is around 65%-70% of the furnace’s total capacity.
Two-stage furnaces are designed to run on the lower setting the majority of the time to conserve energy. The furnace will always start running on the lower setting. It will then switch to full power if the house is currently more than a few degrees cooler than the temperature set by the thermostat. It will also switch to full power if the temperature doesn’t start to rise within a set amount of time, such as during periods of extreme cold.
Instead of frequently cycling on and off, variable-speed units typically operate almost continuously throughout the day and night. Once the house reaches the desired temperature, the furnace will operate at the lowest possible speed. If the temperature ever starts to drop, it will then slowly ramp up its speed to bring the temperature back up before then slowing down again. Despite running far more each day, variable-speed furnaces tend to use far less energy overall compared to single-stage and two-stage units.
Pros and Cons of Variable-Speed Furnaces
The biggest advantage of installing a variable-speed furnace is that it can significantly lower your heating costs. If your house is adequately insulated and mostly airtight, your heating costs will typically be around 30%-40% lower than they would be with a single-stage furnace. Part of the reason is that variable-speed furnaces consume significantly less gas when operating at lower speeds. Variable-speed blowers also consume much less energy when running at a lower speed. In most cases, the blower’s energy consumption drops by around 75% when it’s running at half speed.
Another reason variable-speed furnaces use significantly less energy is that they don’t continually cycle on throughout the day. The blower in a single-stage furnace typically draws around three to five times as much power when starting up, as it must immediately reach full speed. This higher power demand doesn’t last all that long. Nonetheless, it quickly adds up when you consider that single-stage furnaces usually cycle on two or three times each hour. Variable-speed furnaces don’t have this issue because they may cycle only a few times a day at most. It’s also because the blower starts running at a fairly low speed and doesn’t draw excess power.
Another issue with single-stage furnaces is that they often struggle to maintain a consistent temperature throughout the entire house. When the house is already warm and the furnace just needs to maintain the temperature, a single-stage unit usually won’t run for more than 15-20 minutes. This is enough time to keep the central parts of the house near the thermostat fully warm, but not always long enough to fully heat rooms further away from the furnace. The only way to overcome this is to turn the temperature up, which usually results in the central areas becoming uncomfortably hot. The fact that variable-speed furnaces operate at lower speeds for more extended periods allows them to provide more even and consistent heating from room to room.
The primary drawback of variable-speed furnaces is their higher cost compared to single-stage units. Nonetheless, the amount you can save on your energy bills with a variable-speed furnace will usually balance out the higher upfront cost before the furnace reaches the end of its life. Another thing to be aware of is that variable-speed furnaces are more complex, meaning there are more potential issues that could arise and require repairs. However, you can reduce the likelihood of needing repairs on any type of furnace by having an experienced HVAC technician service and inspect it annually.
Which Houses Can Benefit Most From a Variable-Speed Furnace?
Variable-speed furnaces are an excellent choice for certain types of homes and certain situations. Multi-level houses can definitely benefit from this type of unit, as it will keep the basement from being too cold and prevent the upper floors from frequently being too hot.
Variable-speed furnaces are also the best choice for zoned HVAC systems. Single-stage furnaces don’t work well in zoned systems, as they always produce the same amount of heat, regardless of how many parts of the house the HVAC system is currently supplying with heating. This can result in the furnace shutting down too soon due to overheating, and you then need to wait for it to cool down before it will turn on again.
Variable-speed units are a great option for climates that experience fairly significant temperature fluctuations throughout the winter as well. The furnace can always run at a lower speed on milder days to conserve energy and then ramp up to nearly full speed to maintain a comfortable temperature during extreme cold.
One situation where we wouldn’t recommend investing in a variable-speed furnace is if you have an older house that’s fairly drafty and/or not sufficiently insulated. In this case, the furnace will still have to run at close to full power much of the time, negating its energy-saving benefits. You’ll also still experience frequent issues with hot and cold spots, regardless of the type of furnace you have.
While a variable-speed furnace can be a great option, proper system design and installation are essential for maximizing its benefits. If the furnace isn’t the correct size or your ductwork isn’t properly designed and correctly sized, you won’t be able to enjoy all of the benefits that a variable-speed unit would normally provide.
Kalins Indoor Comfort is a family-owned company providing dependable heating solutions to Sioux City, Iowa, South Dakota and Nebraska homeowners. We’ve been in business for over 100 years and have an expert team ready to cater to your home comfort needs. We’re a Lennox Premier Dealer, and we also carry quality equipment from trusted brands like Goodman. To determine if a variable-speed furnace is a good choice for your home, contact us for a heating installation consultation today!
