In this episode of the Ask Derek Cole Show, Derek answers three homeowner questions. First, he explains why a heat‑pump can freeze: either a refrigerant leak or restricted airflow caused by overly dense (high‑MERV) air filters that starve the unit of air, leading to frost on the refrigerant lines. He advises checking filter resistance before suspecting a refrigerant issue. Second, he addresses a whistling sound heard at vents when the system is off, attributing it to air infiltration either through a leak in the crawl‑space grill or a leak in the ductwork, both of which allow outside air to travel upward and create noise. Finally, he stresses the importance of a heat‑loss/heat‑gain (load) calculation when sizing a new HVAC system, noting that reputable contractors perform this on every install, it may be required by licensing boards, and it ensures the unit is properly sized for the home’s current envelope, protecting the long‑term investment.
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Hey, on this episode we talk about what causes my unit to freeze, why am I getting a whistling noise when my air is not on, and what is a heat loss/heat gain? You ask your comfort and energy questions and they get answered. This is the Ask Derrick Cole Show. Hey, this is Derrick Cole. Welcome to episode 61 of the Ask Derrick Cole Show. Derek Cole Show answering your home and energy questions, and we have a few today, right? We do. So let's get right into it.
What causes your unit to freeze over when you have the heat on?
So you got a heat pump, I'm assuming. Uh, if it's a heat pump, refrigerant still can flow back and forth, uh, so you could have a refrigerant leak causing the unit to freeze, or you could have an airflow problem. What I've seen in that regard are people who are buying filters that are high rated in MERV rating, which means they're very allergy efficient filters. But the problem is they're also stopping up the airflow as it comes into the return grill. So when the unit starves for air, freezes up. You see that if you go outside to your unit, you'll see the frost and the ice buildup around the refrigerant line. That's because it can't breathe. It's trying to run a marathon through breathing out of a straw. It's not working out very well, so therefore it's freezing up. So usually those are the two big problems: refrigerant and a lack of refrigerant, or it's leaking, and airflow. So I would check First of all, check your air filter. I mean, it should be a gentle tug to get it out. It shouldn't be, you know, bear against the wall to get it out of the return grill. It shouldn't be that hard because there's always a trade-off between buying a high-quality filter and then having airflow. So with air cleaning, you can do both, but with regular filtration, you cannot. There has to be a give and take. You can't have the best filter and get the best airflow from an air filter. You can when you start air cleaning, but not with a filter. So check that one, that would be easier. If it's not that, then you have a refrigerant problem.
Sometimes I can hear a kind of whistling sound by my vents even when my heat is not on. Does that mean that I have a leak or a broken piece of duct?
It could mean both. If you're getting whistling from the grill from under the house, I'm assuming is where it's at, under the house, then it's probably windy or outside and it's coming into your crawl space and then coming up because air does travel up. If you don't believe me, check out the next person smoking a cigarette and see where the smoke goes. Will go up. So yeah, you have a leak under the house or the air is getting in there and then coming back up, and then you have a leak in your duct system, which is allowing that air to come up. So you could have a leak around that grill under the house, or you could have a leak in the duct system coming up under the house. So does that make sense? So you could have two possibilities. Problems there, or one problem. Either way, you got a problem. Either way, either way, there's an issue. There is an issue either way. But, um, yeah, there is, you know, excessive air coming through if you're hearing a whistling noise.
I was recently told that when getting a new estimate for a heating and air conditioning unit, I should ask for a heat loss calculation. What is that, and is it important?
I will tell you what separates the companies from each other. The companies that provide a heat loss calculation and the companies that do not. That will tell you pretty quickly who you're dealing with. On every install, we do a heat load calculation, which is a load calculation on your house to make sure that it is the right size unit going into your house. Now, it doesn't matter if you had a 4-ton unit for 25 years in your house because we still need to do one. And because you probably replaced the windows, the doors, add insulation, replace the roof, got more insulation, something has changed in that space. So we're just going to calculate again what is needed, how much heat loss or heat gain your house has.. That will allow us to properly size the unit and then we'll put the unit into your home. A company that does not provide this is one that's not doing it and you probably don't want them doing your home because it really does separate companies, you know. We do one on every install. If you're a state license holder, you have to do one. If the state board were to come in here and say, hey, So-and-so customer said you guys installed a 3-ton, it should have been a 2.5-ton. Let me see your heat loss, heat gain. And then boom, you gotta show it to them. So you have to do one on every install and you should do one. And regardless, you know, I've heard it many, many times, same unit I've had for 30 years, 20 years, 15 years. I understand, I get it, I understand that, but this step needs to be done just to make sure I mean, it's going to take another 15, 30 minutes, and this is a 10-year investment at least, so let's make sure we're doing it right the first time. All right. That's it. All right, episode 61. So if you have any heating, air, energy questions, home questions, hashtag them #AskDerekCole, Facebook, Twitter, and Instagram, and we'll get them on the show.
