BY GEORGE LANTHIER

Figure 1

In this article I would like to touch upon one of the biggest problems that I have seen with draft inducers since I started in 1967 and still continues. Many of us are familiar with the proper use and application for draft inducers, but how many of us know how to control them? The powerventer doesn’ t seem to suffer as much from these control problems because most of them are sold with packaged controls. This is an older article that we updated based on a request.

Most of the draft inducer problems that I have seen are because they were not installed to Code, with an absolute minimum of controls that being an air proving switch, Figure 1. This is the most important control since if the inducer fan motor fails or there is a complete failure of the inducer due to blockage, the pressure switch will prevent the burner from operating. And answer me this. Why would you want to run a burner without proper combustion venting? Keep in mind it is at least a Code violation and probably not a good idea. The air pressure switch shown in Figure 1 is a standard model which can normally be supplied by the manufacturer of the draft inducer, nothing special here. There is a small diaphragm inside the case which when pulled upon by the vacuum( negative pressure) created by the fan wheel again closes an electrical circuit. If the pressure is lost because of a failure of the fan motor the

Figure 2

switch opens, and the burner stops.

Another problem has to do with making sure that the air flow( draft) is proper at both the beginning and end of the burner’ s operating cycle. In Figure 2, we have an installation which incorporates all of the elements that we could use to make sure that there is an adequate draft supply at all phases of the burner’ s operating cycle while using a draft inducer. Although this picture is for oil, the rules remain the same for gas. In addition to the inducer there should be that air-proving switch and possibly a time delay and an oil( or gas) valve, found on the burner. This will ensure that there is adequate draft at burner startup and also help promote a clean shut down of the burner and become even more important if something fails. In many cases the inducer and controls may be an integral part of the appliance, Figure 3. Using Figure 3 we can find the inducer( 1), the exhaust outlet( 2) and the air proving switch( 3) on the gas furnace shown.

The air pressure switch, Figure 1, which is normally found on or close to the draft inducer, Figure 4, will not only verify

Figure 3

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