1 Helpful?

ERV ducting - how to insulate?

We have an ERV, which works great for our house, which is in a cold climate (i.e. this week will be below zero at night for the next four days, and teens during the day). This is our second winter in the new house. We have discovered that due to location, a hot water line (PEX with R-4 insulation) crosses over the ERV incoming duct in the between-floor truss level. It has frozen at this point.

We have already tried separating them with spray foam, but it has frozen again. We also found frozen condensation in the vicinity. Thermal envelope is about R-30 and includes 2-inch extruded polystyrene, so the truss zone should be warm - apart from the duct cooling effect.

How do we get enough insulation between these lines? Are we going to have to tear out the whole ERV inflow duct and replace with an insulated smaller diameter line? Currently 6 inch flexipipe.

Any suggestions? thanks in advance for your help.

Asked by Richard and Miranda Menzies
Posted Jan 12, 2013 7:35 PM ET


2 Answers

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The temperature of the air in the fresh air intake duct that brings outdoor air to your ERV is the same as the outdoor temperature. If it's -10°F outside, then that's the temperature of the air in the duct.

So, it is absolutely necessary to insulate this duct. If a water line is near this duct, the water line will freeze, as you have discovered.

I suggest you read the following article: Installing a Heat-Recovery Ventilator. In that article, author David Hansen notes, "Insulated flex duct prevents problems with condensation drips, [so] we use it to connect the HRV unit to the outside vent hoods."

Using insulated flex duct for this section of the duct is easier than trying to retrofit duct insulation on your existing ductwork.

Q. "Are we going to have to tear out the whole ERV inflow duct and replace with an insulated smaller diameter line?"

A. Yes, you are going to have to open up access to this area and replace the duct. However, you shouldn't install a smaller diameter line; you need to install the correct diameter, as required by the air flow rating of the unit and by the manufacturer's installation instructions. If you need to box out the ductwork (because it doesn't fit between the joists), then that's what you have to do.

If you paid a contractor to do this work, the contractor made a mistake. The contractor should return to your house and perform the necessary repairs, at no cost to you.

Answered by Martin Holladay, GBA Advisor
Posted Jan 13, 2013 6:36 AM ET


Thanks for your response - very helpful. We will contemplate these changes when the weather warms up.

Answered by Richard and Miranda Menzies
Posted Jan 13, 2013 6:14 PM ET

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