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Community and Q&A

Central vac in an airtight home

airfix | Posted in Mechanicals on

Just thought I’d run by the use of a central vac in an air tight home by the experts on this website.

I’m assuming because a central vacuum system draws air in from inside the air control layer and expels it into the mechanical room which is also inside the air control layer there are no issues with having a central vac in an air tight home.

New Build
Climate Zone 6A
Pretty Good House
Exterior Foam
Target 1.0 ACH

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  1. Expert Member

    Are you sure it doesn't exhaust to the outside? I've only installed a couple of them, but they both did.

  2. user-2310254 | | #2


    Ideally you would locate the motor unit in any outdoor room or garage. One reason to have a central vac is the ability to exhaust vac air to the outdoors. I don't know how good your vacuum bag might be, but I suspect it fails to trap a lot of nasty material.

  3. airfix | | #3

    You know I'm not sure where it vents. My contractor has it as a line item on my budget (I'm sure my wife had something to do with that). I thought I'd better try figure out the technical details.

  4. GBA Editor
    Martin Holladay | | #4

    Steve Mackay,
    I'm going to disagree with Steve Knapp on this one.

    If you install a central vacuum cleaner, the ideal location for the dust collection bag is in the basement (or, in your case, in the mechanical room) -- that is, inside the home's conditioned envelope.

    If, instead, the dust collection bag is located in the garage, the house will be depressurized every time you run the vacuum cleaner, raising the possibility that any atmospherically vented combustion appliances (like a gas water heater) will backdraft.

    Some people like the idea of locating the dust collection bag in the garage. If you do that, it's important to remember to crack a window every time you vacuum.

  5. Jon_Lawrence | | #5


    Google recirculating central vac, I saw a couple of manufacturers at IBS this year but I can't remember the names. The dust collection bag and exhaust are inside the thermal envelope. They use a HEPA filter on the exhaust. My old school central vac has the dust collection bag in the basement, but it exhausts to the outside. On a separate note, I liked the hide a hose feature they offer now. The hose retracts back into the tubing for storage.

  6. atburi | | #6


    Just digging into this exact same question with my build right now, as well. Did you end up installing the central vac in the mechanical room and did it vent to the outside? Any issues with pressurization?


  7. Expert Member
    DCcontrarian | | #7

    "Airtight" homes aren't really as tight as you think. A quick Google tells me that a central vac moves about 100 CFM. That's not going to be an issue.

  8. scsiguy | | #8

    The solution I used for my tight house was to mount the head unit inside, exhaust to the outside, but use a current-sensing relay on the vacuum to trigger the same makeup air damper that is tied to our range hood.

  9. atburi | | #9

    Good to know. If we do end up running the exhaust outside, I'm trusting that our Zehnder ERV is able to sense the change in pressurization and increase its air flow rate. Apparently, they can do this.

    However, I'm leaning toward not running the exhaust outside and just having a Hepa filter and keeping the exhaust inside (in our mechanical room).

    1. scsiguy | | #10

      My house has two Zehnder ComfoAir 350s. The Zehnder ERVs have a range hood program, which I'm sure you could use a relay to trigger, but given the infrequent use of the vacuum or range hood, and the desire to have an effective range hood (XtremeAir @ 900cfm max), the make-up air damper seemed a simpler/better solution for our house.

      The discharge from our Canavac unit, even with their supplied muffler, is pretty loud, but this is outside the building. I'm glad we can't hear that inside!

      1. atburi | | #11

        Thanks. I'll speak with our local tradesperson about the option of having a make-up damper. You're right — the Small Planet Supply rep that I spoke with about the Zehnder ERV mentioned the range hood program but we didn't discuss the effect of a central vac would have on the system. For reference, Small Planet suggested a Zehnder ComfoAir Q450 for my house (2 floors, 3,000 SQFT) at just under $20K. Much more than we were hoping to spend but, based on comments and reviews, it sounds like Zehnder is the way to go.

  10. scsiguy | | #12

    I haven't looked at the specs for the Q series, but the Q450 may be undersized for your application.

    Our house has 3477sqft of conditioned space with one ERV for each floor (the analysis at the time was that the ComfoAIR 550 was ~10% undersized for us). Based on my findings using a portable Aranet4 CO2 monitor, I have to run the ERVs at 60-70% continuous to ensure the bedrooms stay below 1000ppm with the door closed. This is 20-30% higher than the values from the original commissioning (performed by the Zehnder rep in Colorado) and is required even though we have over-door pass-through grills and have adjusted inlet/outlet flow rates to match room sizes.

    The Zehnder systems are pricy, but exquisitely engineered, quiet, and easy to install. My only minor gripe is that the bearings used in the fans, at least for the 350s we have, are not the greatest. I've had to replace bearings in two fans so far. Fortunately, these are a standard size ($20/fan for premium bearings) and user serviceable for the somewhat handy. If you don't know or figure out that you can just change the bearings, you're out $300 to Zehnder for a complete fan assembly. :-(

    1. atburi | | #13

      Good insights. I'll bring that up with our Zehnder rep to make sure we're not under-sizing our system. Also good to know that Zehnder systems are worth it... given how airtight homes are getting, seems like it's worth the investment for good air quality.

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