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© 2004-2017 John Ford

 
Become an Educated Energy Consumer    OttawaEnergyAudit     Friday 15 December 2017
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Published Columns: October 2004
Curbing Your Consumption:
Q: Should I buy a DC furnace fan?

By John Ford

People who want to circulate air in their homes even when the furnace or air-conditioning is off often install two speed or variable speed fans in their furnace. Running a fan continuously gives some advantages to comfort especially in homes with variances in heat loss as it evens out the temperature. Multi-speed fans can run quieter since they run longer at slower speeds.

Fans require energy however, so how you intend to use it should be a factor in what type of fan to buy. There are a few choices: traditional AC induction motor (PSC) with two speeds, variable speed AC (SCIM and SRM), and variable speed DC (ECM). variable speed motors are more efficient than single or dual speed motors, but the controller is typically on all the time. Compared to a standard single speed AC induction motor , a high efficiency PSC can save 14%, an ECM 25%, and a variable speed ECM 75%. If you intend only to use lower speeds for a small number of months or weeks of the year, it may not be cost effective to pick a variable speed motor which has an always on controller and costs more to buy.

If you are a heavy user of air-conditioning, keep in mind that inefficient motors give off that energy not used as heat, which creates a bigger load on your A/C (and more cost). An inefficient blower motor could be the equivalent of running a 200 watt heater inside your air-conditioner. That's the same reason a newer, and more efficient refrigerator will also lower your A/C costs. An old fridge could be putting out 500 watts in the form of heat into your kitchen which then requires 1000 watts of A/C to cool.

Before you make your decision, speak to your heating and cooling company and compare the numbers for the available options based on your own usage patterns.

Ask the Miser
If you would like to see answers here to your questions about energy consumption, email them to questions@oea.dyndns.org

John Ford is a technology consultant, and owner of a small energy conservation business.