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Installing Central Air in an Old House

  • Transcript

    LESLIE: Talking to Ernest in Pennsylvania about air conditioning. How can we help you?

    ERNEST: I’ve got an old house. It was built in the 1800s. It’s a row. And the heater was – the hot air heater was put in around 1962 …

    TOM: OK.

    ERNEST: … using existing ducting from the gravity-fed heater.

    TOM: OK.

    ERNEST: I’m considering putting in whole-house air conditioning.

    TOM: Mm-hmm.

    ERNEST: How much of a problem is that going to be?

    TOM: Can’t do it. That duct system is going to be way under sized for air conditioning. The air conditioning ducts have to be a lot bigger.

    ERNEST: Well, these are like 24×8 inches.

    TOM: OK.

    ERNEST: They boxed in the joists.

    TOM: Mm-hmm. Typically – well, that’s probably for the return. That usually wouldn’t be for the supply. You probably have another type of duct for the supply.


    TOM: But typically, these old houses that only had heating systems and not air conditioning, it is very unusual that you’ll be able to install a central air conditioning system into that and use the same size ducts because they’re typically too small and inefficient and they don’t do the job. And I don’t think you’re going to be happy.

    Now, that being said, there may be some not too terribly complicated changes that could be made to improve that duct size. But you need to have an HVAC guy take a look at that – a heating, ventilation and air conditioning contractor –

    LESLIE: Mm-hmm.

    TOM: – because that’s all part of a sizing calculation …

    ERNEST: Right.

    TOM: … that plays into the size of the compressor that you’ll need and the size of the ducts. Generally, though …

    LESLIE: Now what about – I’m sorry, Tom. But what about, you know, a separate system? Maybe something like that SpacePak company that uses those smaller, you know, flexible …

    TOM: Well, you could put a completely – yeah, you could put a completely separate system in but, you know, I tend to think that that will probably be more expensive than improving the duct system you have right now.

    You know, there’s a lot of tricks of the trade to this. You can have very, very few bends. For example, if you take one 90-degree bend in a metal duct, that’s equivalent to like 20 lineal feet of resistance. So that’s like adding another 20-foot section in terms of how much oomph it needs to get around the corners. You know what I mean? So I think you’re going to have to do some modification to those ducts.

    ERNEST: (chuckling) I’m stuck with window units, then?

    TOM: No, you’re not stuck with window units. Listen, you can do it. It’s just going to take some work.

    ERNEST: Lot of take walls out and …

    TOM: Maybe not. No. If it’s done carefully it’s – listen, I have a really old house that has a hot water system. So we had no ducts and we were able to get a central air conditioning system installed with very little disturbance of the framing of this house; just because we were very careful and selective about where we ran the ducts. There’s a lot of places to get ducts in a row, Ernest. (Leslie chuckles)

    ERNEST: Yeah. (laughing) That’s cute.

    TOM: Alright?

    ERNEST: Alright, thank you.

    TOM: You’re welcome. Thanks so much for calling us at 888-MONEY-PIT.

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