Learning the Lingo of HVAC

  • changing hvac filter
  • Transcript

    LESLIE: Well, there’s a lot of jargon in the world of HVAC, including those four letters themselves. And all this confusing alphabet soup sometimes gets in the way of shopping for, maintaining or fixing your heating-and-air-conditioning systems.

    TOM: Well, here to tell us how to decode the HVAC lingo is Richard Trethewey, the plumbing-and-heating contractor on TV’s TOH, This Old House.

    RICHARD: Giving away all the secrets? I can’t do that.

    TOM: Hi, Richard.

    RICHARD: Hey. How are you?

    TOM: So, it’s a question that we hear a lot. What do all of these letters mean in the acronyms that are associated with your heating-and-air-conditioning systems? So let’s start with the basics: HVAC.

    RICHARD: It is like alphabet soup, isn’t it?

    TOM: It is. It really is.

    RICHARD: HVAC. So that’s heating, ventilating, air-conditioning. And so we’ve shortened it to HVAC but it’s sort of the all-encompassing world of I’m going to heat it, I’m going to cool it, I’m going to put some fresh air into it.

    TOM: And that’s part of what confuses people because I think that folks don’t recognize the importance of the V part of that, which is ventilating.

    RICHARD: Yeah. Ventilating is critically important to get fresh air, particularly as you make these buildings much tighter.

    LESLIE: Now, there’s a lot of other acronyms in the HVAC world.

    RICHARD: Oh, yeah. There’s a whole book of them. Yeah.

    LESLIE: So let’s talk about them. I hear the term MERV a lot.

    RICHARD: Yeah. I loved him.

    LESLIE: Yeah, Merv Griffin? Great guy.

    RICHARD: He was so good.

    TOM: He was such a great host, yeah.

    RICHARD: He used to have Charo on all the time.

    LESLIE: Cuchi cuchi.

    RICHARD: So MERV actually stands for minimum efficiency reporting value. And this is an important measurement for how good is a filter. There’s a test standard and so you’ll be looking for some ratings that run from MERV 1 to MERV 16. But most of them are sitting – the decent ones are all sitting at MERV 7, 8 and 9.

    Now, when you have a higher resistance, be careful. If I have one that’s got so much resistance that every bit of dirt gets sucked – gets absorbed in it, it might be so hard to push air through that I have to have a bigger blower. It doesn’t work. So you have to – this number – just getting the highest number is not the answer. You’ve got to get the right answer.

    TOM: Not always the best.

    RICHARD: Right.

    TOM: Right. So you have that right combination of efficiency and airflow.

    RICHARD: That’s right. Right. Yep.

    TOM: Now, what about SEER? That’s another common one – S-E-E-R. That’s an important number that is often used when you’re buying an appliance, because it’s usually stuck on the yellow label in front of it, right?

    RICHARD: Yeah. In the efficiency world, there’s all sorts of SEERs, there’s an EER. So, seasonal energy efficiency ratio.

    TOM: So that’s SEER – S-E-E-R.

    RICHARD: OK, SEER. And then there’s the energy efficiency ratio. And there’s a million of them that all talk about how efficient it is. And so, one is how much of the fuel that I bought and burned became usable heat? But the seasonal energy efficiency ratio is really about how over the course of a season – and hence the word “season” – how efficient it will be. So it takes into account weather occurrences that it was tested under. And so, when you’re talking about air-conditioning, they’re going to measure the air-conditioning condenser outside.

    Now, there was a time that we had SEER of 8 and 9. And now, we have minimums of 13 SEER. Now, 13 SEER is what you want as a minimum. It gets up to 18, it gets up to 22. And I’ve got to caution you that as you get higher efficiency, the units get physically bigger, bigger, bigger, bigger, bigger, bigger because they’re trying – the way that they’re doing it is they’re dividing the amount of cooling power divided by the electricity.

    LESLIE: Larger.
    TOM: Oh, is that right?

    RICHARD: So if they can have a much bigger fan that has just a gentle motor in it, then it’s going to have less electricity and more return.

    LESLIE: I think I got one of the first SEER 16 condensing units.

    RICHARD: Yes. Yep, yep.

    LESLIE: This was probably eight years ago?

    RICHARD: Yeah. Was it big?

    LESLIE: It’s as big as my house.

    RICHARD: Yeah, that’s right.

    LESLIE: So I have this super-tiny, little Dutch Colonial with this enormous condensing unit outside. I mean it’s kind of comical.

    RICHARD: Yeah, yeah, yeah, yeah. As Tommy Silva would say, more is plenty.

    LESLIE: Now, speaking of more, let’s talk about A/C tons. I think people think that there’s the weight of the physical container itself.

    RICHARD: Oh yeah. Yeah. Yeah, they don’t think we should be able to carry the equipment in because it weighs 2 tons.

    TOM: Two tons, yeah.

    RICHARD: It weighs 2 tons. And that actually goes back to the old days when the ice man was in play. And there was a – it was a measurement when they have an ice house, how many tons – how much heat would it take to melt a ton of ice?

    TOM: Oh, is that right?

    RICHARD: Absolutely. It goes right back to that (inaudible at 0:27:57).

    TOM: Wow.

    RICHARD: And so, I will tell you that it’s a measurement of a ton. It’s the cooling power that you have available to you. I will tell you that in New England, anyways, you need a ton of cooling for every 600 to 700 square feet of space. It’s a typical thing. With these modern houses, they’re getting super tight. We could go up to 800 or 1,000 but the typical house built here. And so it’s got nothing to do with the weight of the equipment; it’s a question of the size.

    And I want to caution you. On this issue of tonnage, you want to get the right amount of cooling power. More is not better. More is not better. Everybody says, “Oh, how much for a 2-ton system? OK, how much for a 3-ton system?” And then when you tell them a 3 ton, they say, “We’ll take that,” as if they’re getting a deal.

    TOM: Right.

    RICHARD: And if – but if the load – if what the building needs is 2 tons, if you put in one that’s 30 percent too big, it’s the worst thing you could ever do.

    LESLIE: Because it never turns off.

    RICHARD: It’s on and off.

    TOM: It cycles.

    RICHARD: No. It’s on and it’s off, it’s on and it’s off. And it never stays on long enough to actually pull out the humidity. So now you’ve got cold but no humidity removal. And half the battle to be comfortable is to get that humidity level to a reasonable place.

    TOM: You get that cold, clammy feeling all the time. Yeah. That’s a great point.

    RICHARD: That’s right, that’s right. Those are tons, yep.

    TOM: Now, let’s talk about some newer systems that are out there. Not so much newer to the world because these have been used in Europe for decades at this point. But we’re starting to see them more widely distributed in the States. And that’s the system called the “ductless mini-split unit.”

    RICHARD: Right, right. So, the acronym that some people call it is DFS – duct-free split. And ductless mini-splits. And you’ve seen them. They read like the who’s who of Asian manufacturing. They’ll have a cassette up on the high side wall or they can be ducted. And unlike the other typical domestic systems we already had, which was a furnace with a series of ductwork going through to every room and returns from each room.

    TOM: Right.

    RICHARD: And you try to balance it and it would never have the exact temperature you want it to.

    Duct-free splits are light – have either a single box outside connected to a single box inside and all you have to run between them is two relatively small refrigerant lines and electricity. Or you can have a single box outside and up to 4 or 5 – or in the commercial world, you could have 100 different inside boxes connected to 1. And now, you can get localized zoning, quiet, really efficient both heating and cooling.

    TOM: So lots of things to know when you are purchasing a new HVAC system.

    RICHARD: Yeah.

    TOM: Fortunately, we’ve got Richard Trethewey from TV’s This Old House to help us sort out all of this alphabet soup.

    Richard, thank you so much for stopping by The Money Pit.

    RICHARD: Yeah, yeah.

    TOM: Great advice.

    RICHARD: Yeah. Just always say the name Merv and (inaudible at 0:30:40).

    TOM: Merv, right?

    RICHARD: Merv.

    TOM: Got it.

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