Good evening inspection heroes, I have not seen many electric furnaces, don’t think they’re too common around here. All of a sudden I had two inspections with electric furnaces and they both had what appeared to be a fresh air intake. A vent on the roof, flex pipe coming down to above the furnace filter complete with damper inside. I cannot imagine why there is a need for the fresh air intake so hoping somebody can explain that and I would be grateful. All I did was take a pic of the damper and not the whole rig but there is really nothing to it but the flex pipe terminating directly above the furnace over the evaporator and leading up to the vent. I just cant think of a reason, both setups were identical and Im sure there is one (reason)
thank you
mike in MN
Most of the time there is no need for outside air the reason for the damper but some folks like to operate just the fan on constant run and draw outside air in when the exterior ambient is moderate early spring early fall
Charlie that is an excellent answer and gave me ‘aaaahhhhh…sure’ moment, but now I’m wondering (since the damper is not lockable that I could see) what about in the dead of winter and you’re drawing subzero air into the furnace and hot summer days when there is heavy wet hot air being dumped over the AC coils? That can’t be too conducive to efficiency. Seems that the fresh air concept, though a cool idea, only works during a small portion of the year. Unless this is a concept which is more common in the temperate zones of the country…and installers are simply and without considering consequences, setting up the unit per those recommendations (for a temperate climate zone). There should be a means of closing the damper during those times when one does not want the outside air.
your input please
mike in MN
Fresh outside air is also used for make up air and or to pressurize the building envelope relative to outside, and or to facilitate air changes, and or to reduce humidity in buildings in cold weather.
Electric furnaces do not need combustion air, but the house they are in likely has exhaust fans, air leakage through stack effect, and possibly construction tight enough to need help with air changes.
A motorized damper tied to an exhaust fan could automate opening and closing of the damper.
An HRV unit does all this stuff automatically as well as recover some heat from exhausted air and would probably be the thing to recommend to a homeowner who has a tight house or is planning to make the house tight.
We were not told if this was a manufactured home or not. If it is manufactured this intake also works with timed vent fans (in bath or a hallway) to combat the formaldehyde off gassing hazards. The setup shown has no direct connection to be able to draw outside air for direct fresh air circulation through the home. The air can only draw in when a negative pressure zone is created in the home (or go out when a positive pressure condition exists). Negative pressure is most commonly created by any fan venting to the outside or leaking ducts in an unconditioned space.
quite sure I don’t understand what you are getting at but would like to know. (always up for learning something) …this is the first time Ive heard ‘formaldehyde’ in an HVAC conversation but I have not read all by any means. It is a manufactured home as was the other where I saw this setup. Definitely a direct connection to a vent in the roof, unless within the insulated flex vent there is some gizmo which cannot be viewed, I never discount the unseen. The damper was simply a rotating metal plate which presumably opens and admits outside air when the circ fan is running since it is located directly over the furnace filter on top, …the house air intake. Do not see how it could be synchronized with other in house fans. and still wonder about the logic of pulling hot wet exterior air over the evap coils or subzero air over the heating coils.
always open to being enlightened,
mike in MN
You have a point about unconditioned air, but in many cases having fresh air is more important than having heated, cooled, or dehumidified air. This is especially true for new houses and and manufactured houses
HVAC stands for heating VENTILATION and air conditioning. New homes are built far more air tight than ever and building materials are more likely to off gas vapors like formaldehyde and other gases that may contribute to health problems.
The solution is to mechanically exchange the inside air with outside air.
In residential houses this can be done with an exhaust fan and the air handler that normally circulates conditioned air (heated, cooled, filtered etc.,) by providing it with an outside air duct. This is the low end solution and must be operated manually by the homeowner through a damper that controls the amount of air coming in from outside and manually operating an exhaust fan. It will also work when the air handler fan is on by creating positive pressure in the house, forcing air out through cracks or the exhaust fan ducts. Slightly better is a system that automatically turns on the air handler’s circulating fan when a designated exhaust fan is turned on. This now meets the minimum code requirement for new residential in Canada. Better yet is using an HRV (Heat Recovery Ventilation) system that replaces exhausted air with incoming air and uses the exhausted air to exchange heat with the incoming fresh air, independent of the heating or cooling system.
Best of all for air quality, found in commercial and industrial applications, is an independent make up air unit that conditions fresh air brought in to replace exhausted air typically found in places that have large exhaust fans, such as commercial kitchens,shops with paint booths, welding or fume extraction, etc…