In this Ask Derek Cole segment, Derek explains that selecting an HVAC filter is not a one‑size‑fits‑all decision. The appropriate filter depends on the home’s construction (tight vs. leaky), the ductwork’s size and condition, and the system’s ability to handle airflow resistance. He contrasts cheap, low‑MERV filters that barely capture fine particles with high‑MERV filters that can restrict airflow if the system isn’t designed for them, leading to issues such as filter collapse, air bypass, and reduced efficiency. Derek also recommends considering whole‑home air cleaning devices, which capture very small particles without adding significant pressure drop. When a return grill whistles, the likely cause is an undersized return duct or grill, often compounded by an overly restrictive filter. He cites code requirements (e.g., multiple returns for large homes in North Carolina) and stresses that a qualified HVAC technician should assess the system during routine maintenance to recommend the optimal filter and address return‑air sizing problems.
Chapters
Now, I do always recommend air cleaning, which is a different type of filtration than a filter, but if you're going to use a filter, you want it to be the right one. You ask your comfort and energy questions and they get answered. This is the Ask Derrick Cole Show.
What filter should I use in in my house?
You should use the best filter for your home. And let me explain this because it's kind of hard to understand. It depends on your house and your duct system as to which filter you need. Now, I do always recommend air cleaning, which is a different type of filtration than a filter, but if you're going to use a filter, you want it to be the right one. You go to the box store, they got like 2 rows of filters. I'm sorry, 2 aisles of filters really, because you got the cheap one for like a dollar and then you got like the $30, $50 filters. You're like, well, that one must be better because it's that much. But your system will determine what filter it can handle. So if you have a tight home, a newer home, and it's a tight construction, energy-efficient construction and your duct system is tight, then putting a really high MERV-rated filter in that system could cause more problems than good. So you could put in a filter that stops up the airflow, which is a problem. On the other side of the spectrum is a cheaper filter or a cheap filter, 80-cent, dollar filter you put in there and it's not very good at all because the only thing it's stopping is sandwich bags and Coke cans and anything else you throw at it. Yeah, it's 100% efficient at stopping that, but 98% of what we're trying to stop are the particles you cannot see. So if you look at your TV or your cabinet and you see dust on it, we're not trying to filter that because it's so heavy it's sitting there. You're trying to filter the particles in the air. That are coming through, and those you cannot see. So you need a better filter for that. Once you get into air cleaning, then you actually stop filtration and go into air cleaning. And the reason you want to do that is because now you're getting the small particles you cannot see, and you're not stopping up your duct system. So if you go to the filter on the return grill and it's too tight and the filter is getting sucked in, then the filter is too much for that system to handle. So you need to go down in filters. I mean, it's a case-by-case basis. I mean, some houses are older, they're very open, the duct system is very leaky. You know, they can handle a MERV 15 filter in there because they're leaking so much air, very few of that, very few very small amounts of air are coming through that anyway, so it's not stopping it up. Um, it's kind of a complicated answer, but it really depends on what kind of system you have. The best thing to do is get the technician when he does your maintenance every year, it's just check your system and recommend what filter is better for you because some are good, some are bad. It really depends on your situation. I don't even think I answered that question. I went around in circles. It depends. I mean, it really does depend. I've been to a house before and his filter was too good. So I opened the filter grill and the filter is getting sucked in and the air is bypassing the filter and going through the four corners and not through the filter. So, you know, you're defeating the purpose of what you're trying to do, which is filter the air. It all depends.
Why is my return grill whistling when my air is on?
It's whistling because your filter is too good. No, no, it could be that. It could be your return side duct system is too small and your filter grill is too small. Bigger is better when it comes to your return. So if You really, for all purposes in a residential application, you really can't have too much return or too big of a return grill in your house. So the return grill is too small, therefore your return duct is too small, and therefore the air is whistling as it goes by because of a tight fit. So check your filter and probably your return duct is too small in that situation, therefore your return grill is too small. We go to a lot of homes. Where we go to change out a unit and the return grill is too small. It's not sized properly. Actually, in the state of North Carolina, if you have an over 1,600 square foot house and you change out the duct system, you're supposed to have more than one return. So we've run into that a few times and we run into the situation of the return grills is too small. So you're not returning enough air back to the system. So the system itself is sucking in air from outside, under the house, in the attic, through the walls, whatever it has to do, it's getting the air to the unit. But, kind of go back to the filter question, you want it to be clean conditioned air going back to the unit and not hot, humid, or cold outdoor air. Going back to the unit, which is not filtered. So it goes hand in hand, filter and return.
