January 9, 2017
Last July I got a new A/C and furnace; everything was replaced except the refrigerant lines and, obviously, the ductwork. The lead installer told me to change the filter once a month and the other installer told me to change it once every three months. I got them together to discuss which is better.
The lead installer said the filters need to be replaced more often when the HVAC (Heating, Ventilation and Air Conditioning) is new (now) than when it’s older (20 years from now). He also said, FWIW, that today’s HVACs are smore sensitive to clogged filters than they were 30 or even 15 years ago.
The helper installer argued that the older the unit is, regardless of when it was installed, the more often the filter should be replaced, not the less often.
Does anyone here know who is right, if either?
What I suggest is that you check the filter every 30 days and see if it needs to be changed, and how often.
A new system’s filter usually need to be change more often during the first few months. The new motor probably has a higher velocity airflow, and will probably suck out some of the old dirt. When the filter shows signs of becoming clogged, change it as needed, or every three months.
I would ask the installer/manufacturer which MIRV (Minimum Efficiency Reporting Value) rating of filter they recommend for you furnace. The higher the number, the more efficient the filter. The more efficient the filter, the harder the blower motor has to work to exchange a building’s air.
The frequency with which an HVAC filter should be replaced is dependent upon the amount of particulate matter it is filtering, and not the unit moving the air.
A new home is likely to have a lot of stuff in the distribution ducts, although better builders do try to vacuum it out. But if it’s a new HVAC unit in an older building, this would not apply.
In general HVAC filters protect the HVAC unit from getting crapped up with particulate matter, and perhaps to a lesser extent improve air quality for the homeowner. Filters with higher MERVs are supposed to improve air quality better for people. Maybe. However they also provide greater resistance, diminishing airflow and making the blower work harder. I have heard HVAC people say the blower wears out faster with high-MERV filters. Dunno about that…but high MERV filters are more easily clogged up.
It’s my personal opinion that the high-MERV filters have become a contest of who can cater to those convinced that their HVAC is somehow purifying the air they breathe, and that therefore the smaller the minimum particle size the better. LOL on that, but certainly those filters in a dirtier environment would need to be changed more often than a low-MERV filter in a cleaner environment.
Yet another vote for: “It Depends”.
And for “age of furnace has nothing to do with it” - unless the furnace is somehow crumbling into dust which it than deposits directly in front of the filter.
Just by a carton (if you have the space) of standard (your definition of that term, not mine or anyone else*) filters and check every once in a while (months).
At first, you might leave a pen and notepad (which you should buy in bulk) by the filter and note date and condition.
After a year, notice a pattern and use that for your schedule.
This worked on a 1947 furnace with asbestos insulation. It also works in the slightly later model in this dump.
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- in this case, OP’s opinion is the only one which matters - the user’s comfort level is what matters.
Doorhinge, Chief Pedant and usedtobe,
Thank you for taking the time to dispense your expertise.
If you want to keep going, I have another question about HVAC. The A/C and gas furnace are in my basement. Does it matter whether I keep the door to that basement open or closed?
The gas furnace needs to have a source of air for burning the gas. This is called combustion air in the HVAC trade, and this is usually brought in from the outside through two small openings in the wall, or in may be brought in through two small ducts. One of these ducts or opening is low about a foot off the floor, and the other is high near the ceiling. Take a look and see if you can see the combustion air opening in the basement. These ducts can bring in cold outside air, and the door to the room should usually be kept closed. There are exceptions but I don’t think so in most residential cases. However, if you have a high efficiency furnace, the air may be brought directly into the furnace through a PVC pipe.