Renovation & Design

Running HVAC blower a good practice


Setting your new furnace’s thermostat to run the blower on low speed continuously is a good idea, and shouldn’t have negative effects on performance or longevity.

Question: I am planning to get a new mid-efficient furnace and air conditioner this year to replace the originals. I am unclear whether to run the furnace blower fan 24-7, continuously, virtually year round. Or should I just program the thermostat to auto, so the fan operates based on the thermostat-programmed settings? Every HVAC person I ask has a different answer to this question, in relation to wear and tear on the blower fan/paddle-wheel.

Our house is older, but is a contemporary, custom built tri-level. The third level is only an open loft room. It is well cared for, with major upgrades to the kitchen, bathrooms, skylight, roofing, interior painting, etc.

I would surely appreciate your feedback.

Kind Regards, Brian Kelly.

Answer: Running your furnace blower full-time is a good idea to help move air around the home, preventing condensation and moisture issues. However, you don’t need to do it year round, as long as you use your home’s natural ventilation when possible.

I commend you on your ambition to update your home’s older heating system, which will have several advantages. First, the new furnace should be much more efficient than the older model, which will save you money and reduce emissions. That will be good for both your monthly budget and for the environment. I will caution you not to try and look for a "mid-efficient" furnace, as they are no longer manufactured. All new natural gas-fired furnaces are true high efficiency condensing furnaces, some advertised as exceeding 95 per cent efficiency. That means over 95 per cent of the natural gas fuel is converted to heat, leaving only a small amount of waste, normally to exhaust and water vapour.

After the new furnace is installed, another benefit is the increased air flow you should notice at your heating registers. The blower that circulates the heated air through the heating ducts should be more powerful, and with a more efficient design, than in your ancient furnace. This is partially because the heated air in your new furnace is cooler than with most older models, so it requires more force to move the air through the ducts. The warmer the air, the easier it is to push to the registers with the blower. Most new furnaces also have blowers with multiple speeds, or even variable speed motors. This point is important if you are planning on running the fan continuously, because that should not be done on a higher speed setting.

The continuous cycle, which should be settable on your thermostat, should be on low speed, for best performance. This is often accomplished by switching the fan speed switch, or electronic button, to ON rather than AUTO. This will circulate air through the heating ducts full-time, whether or not the heating or cooling cycle is activated. When the heating cycle engages, due to the temperature in the house dropping below the setting on your thermostat, the fan should automatically increase speed. This may happen immediately when a new cycle is activated, or after a short delay. The delay will give the heat exchanger time to warm up after the burner comes on. Once the thermostat setting is satisfied, the burner will shut off, and the blower should eventually return to the lower continuous setting.

There should be little to no problems with you running your furnace blower on a continuously low setting. Several HVAC experts have told me that new blower motors are designed to run continuously and should last for many years, regardless of setting. The newer models are not damaged, or less efficient, running under a heavy load, even with a dirty or more restrictive air filter. So, worrying about burning out your blower motor by running it on a continuous low speed should not be an issue.

The reason to run the furnace fan all the time is to improve the air movement and circulation in the home, even when the heat is not on. Especially in homes like yours, with multiple levels and rooms, air can become stagnant in areas far away from the registers. If the air stops moving, it will cool more quickly, which can lead to condensation, moisture, and mould issues. If the air is constantly being forced through the ducts by the blower, the areas with poorer air circulation will constantly mix with this warmer, dryer air, helping to absorb some of the humidity, preventing condensation on cooler surfaces. It may also improve the air quality, by minimizing dust and contaminant circulation, as long as high-quality air filters are used and changed regularly.

Because air circulation and ventilation are so important in maintaining good air quality, you may not have to run the blower continuously year round. In the warmer months of the year, typically late spring and early fall, natural home ventilation can be achieved simply by opening windows and screen doors. In these shoulder seasons, outdoor air circulating through your home from these sources will have a similar effect to running the furnace blower. So, that is the time when the continuous cycle can be switched to auto on your thermostat. In the heat of the summer, when you close your windows and use the air conditioner by setting the thermostat to cool, the fan setting should again be switched to on. Closing the windows will prevent wetter, outside summer air from entering your home, while the air conditioner and the furnace blower will again ensure good air circulation inside the living space.

Setting your new furnace’s thermostat to run the blower on low speed continuously will be a good idea, which should not have negative effects on performance or longevity. This will not be necessary in the shoulder seasons, as long as you open your windows when the weather is milder, to allow natural ventilation to partially replace the function of the furnace blower.

Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba ( Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at


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