ECONOMIC CENTS: HVAC Systems and Air Flow Go Hand-in-Hand
Dirty filters, built up air pressure cause for inefficiencies in many homes.
by Bruce Saller
GUEST WRITER
The heating, ventilation, and air conditioning (HVAC) system works hard enough on both cool and warm days to keep people comfortable. Don’t make it work harder by restricting its airflow.Â
A dirty air filter can reduce your system’s efficiency by anywhere from 5% to 15%. To maximize an HVAC system, replace the air filter every month or two during the heating and cooling seasons.
Dirty air filters are easy to replace, and critical for maintaining a system’s efficiency. But this isn’t the only thing that can block air flow.
Another issue can be a blockage of the return air path.Â
Most systems have one or two central air ducts that return air to the HVAC unit. Closed doors can restrict the return airflow. To ease this problem, ensure that the gap between interior doors and the floor is between ½ and ¾ inches.Â
If the gap is smaller than that, air pressure can build up in the room causing air to be forced outside through gaps in windows, electrical outlets, lights and bathroom vents. This air is replaced by outside air pulled into other rooms, which then needs to be heated or cooled.Â
It’s easy to determine if air flow is inadequate. Simply close a door until the latch touches the strike plate, and then see if the door quickly shuts. If it does, you have restricted air flow. To reduce or eliminate this problem follow the following steps:
1.     Leave doors open where possible.
2.     If you need to keep a door closed:
a.     Remove rugs from around door bottoms.
b.     Consider cutting off a portion of the door bottom to make a ¾ inch gap.
c.    Close vents in the room no more than 75% of the way.
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True, true, true.
Other things to consider (among many).
Moving furniture away from returns so that air has a pathway back to the air handler. The performance of air handlers are mathematical functions. For it to move 400 cubic feet per minute out - it has to have 400cfm come back into it.
If it doesn't get it thru the designed return ductwork - it will obtain it from elsewhere - such as duct cracks in attics, basements, etc. Not only an energy efficiency issue, but indoor air quality issue.
Transfer grills or jumper ducts installed between bedrooms and the return. Good discussion of it here:
https://basc.pnnl.gov/resource-guides/transfer-grilles
Maintaining the cooling coils. Dust accumulates on them (most filters are primarily designed to protect the coil, not the inhabitants). To remove moisture - they require periodic cleaning (once a year desired, definitely no less than every two years). Get them to check your coolant levels as well. By someone reputable, knowledgeable. Even in new systems, undercharging has been found to be a major cause of inefficiency (up to 20%).
And maybe discuss installing one of the 4 inch filters rather than 1" ducts. Not only do they allow higher filtration levels for longer periods of time between changes (including to levels that will protect your family from things like asthma attacks the next time Canada is burning and you're breathing the result), but the reduced static pressure means your air handler doesn't have to work as hard to get that 400cfm/ton back so it can condition it. Which means less energy used now, and less strain on your equipment long term - which reduces the risk of system failure.
As always, thanks for bringing up. Looking forward to the next one.