Continuous Circulation and ECM Fans

We are used to the fan in the air handler connected to our duct system only running whilst the furnace, air conditioner or heat pump is actually in operation (or for only a short time after it stops to dissipate the heat). You may well think that the less time you have the noise of the fan and the airflow the better. However, there are significant advantages to circulating the air in the house either continuously or for much longer periods than normal and most of the disadvantages such as noise and cost have been virtually eliminated. Consider the following points:

1.Nearly all air systems have some kind of filter included and many people have installed much higher quality filters in situations where animal dander is a problem or family members are particularly sensitive to pollutants (see the Indoor Air Quality Journal [download .pdf - 366k] distributed by Waterfurnace). At times when the heating or cooling system is seldom running the filter system is useless unless the air circulator is run independently of the heater or cooler.

2. Many air systems are designed to introduce fresh outdoor air to the home either directly or by way of a Heat Recovery System. These systems are again useless during seasons when the fan does not run. This is very unfortunate since many studies have shown that fresh air is essential to a healthy life and lack of it leads to drowsiness and inattentiveness in schools.

3. The same thing applies to those homes where the heating is radiant but a duct system is also fitted for air conditioning in the summer. Filtering and fresh air input only occurs when the house fan is running.

4. Houses often have rooms which get either significantly hotter or cooler than others particularly when the heating or cooling system is not running. This can be caused simply by heat rising or to solar heat gain on the southern or western sides of the house or to some other heat source such as people or computers in particular rooms. Simply running the air circulation system either continuously or for extended periods can overcome this problem and even save gas or electricity which might be used to heat or cool a room when its thermostat makes a call.

5. In very cold or very hot weather we need to have plenty of fan power available to deliver the necessary air but in more moderate conditions this is unnecessary and only produces noise and possibly drafts. Lower fan speeds can give much more comfortable conditions as well as providing the filtering and fresh air advantages mentioned above.

6. In a home with several zones for the air system it is important to reduce the power of the fan when only a small number of zones are 'open'. This is difficult to achieve with a standard fan.

It used to be that running the air-handler fan continuously was either expensive or noisy or both. The electric motors in house fans have conventionally been of the PSC (permanent split capacitor) type which either ran at a constant speed or required an energy hungry control device to reduce their speed. The ECM, electronically commutated motor, (developed and patented by GE) has overcome these control and running-cost problems and now delivers efficiencies of 65-72%, even running at low speed, compared to a typical range of 12-45% for a PSC motor. An HVAC system fitted with an ECM fan can now run continuously for about the cost of running a 60W light bulb, a much more economic proposition considering the comfort improvement and the possible reduction in gas or electricity usage by the heat or cooling source. Read a Canadian study on the benefits of ECM fans here.

When selecting your new furnace, heat pump or HRV system it is well worth paying for a model which includes an ECM fan and then either running the fan continuously or for long periods or, ideally, controlled by an occupancy monitor in the house.