Condensation at ERV Intake Collar
My HVAC installer appears to have done a decent job insulating the supply (outside air) duct on my ERV (sealed metal ductwork with duct wrap having metalized foil with interior fiberglass and sealing all seams on the insulation), but last night I noticed some wetness at the point where the insulation abuts the intake of the ERV. The insulation outer layer is not sealed to the ERV itself, so I suspect basement air is making its way into the insulation and condensing on the cold metal duct.
I have a LARGE dehumidifier running in the basement and the humidity is “controlled” for the most part, but still hovers around 50%. This month I’ll start the job of installing interior rigid foam insulation on the interior concrete foundation walls so hopefully that will help with the humidity levels.
Are there any “tricks” in resolving the condensation issue in the meantime? Other than sealing the outer layer of the insulation to the ERV intake collar? Better materials to use? The ERV is set to the ASHRAE CFM rate, would dropping to the IRC CFM rate (about half of the current airflow) help in any way?
I’m in CZ5 with outdoor temps in the twenties recently, basement is around 55 degrees Fahrenheit and around 50% humidity. Thanks for any ideas you have!
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This is a tough detail. Dropping the ventilation rate might help, but the key is to prevent contact between basement air and bare sheet metal. The ERVs I've worked with have a plastic start collar than doesn't provide a lot of attachment area. One thing I've done is use foil-faced bubble wrap to make an 8"-12" sleeve that wraps the duct/unit connection, covering the exposed end of the fiberglass. Bubble wrap doesn't have much R-value, but it will have enough to keep its outer surface above the dew point, which is about 37F in a 55F/50RH basement. If you'd like, you can use a double layer. I would zip-tie it and tape it thoroughly at both ends with foil tape. You can also dovetail-cut the bubble wrap to give you some taping surface on the cabinet of the unit itself.
Thanks Jon, appreciate the info. One kicker is that the supply duct makes a 90-degree turn into the ERV collar, making it pretty tough to do much at the collar end. Taping the bubble wrap to the unit would probably be the best solution in this configuration.
I would cut back the inner insulation so you can make an air tight tape joint without the block of the insulation interfering, and the use a close cell duct wrap tape to insulate the inlet duct up to and around the collar.
You could crack a window in the basement until the humidity drops. If it's in the 20F range outside and your basement is warmer it will have a drying effect, if you don't overdo it, it might be more effective than running a dehumidifier.
Here is a handy dewpoint calculator, that you can use to see if opening a window will help you. http://www.dpcalc.org/
Thanks for the suggestion, Josh; do you have specific brand(s) or products for closed cell duct wrap tape?
On my ERV I had the issue and used a fail faced bubble tape that had some stretch and a good adhesive. It doesn't insulate as well as the duct insulation but it brings the surface temp above dewpoint. You can cut and shape it and wrap it several layers deep. It was something like this... https://www.homedepot.ca/product/reflectix-pipe-wrap-4-inchx25-/1000167780
That's great, thanks for the pointer to the product you used.