There are two types of units that serve the same yet purpose, A Heat Recovery Ventilator (HRV) and an Energy Recovery Ventilator (ERV). Most often you will find HRVÂs used in the northern climates where heating is dominant and ERVÂs used in the south with AC being used more often. The big difference between the two is an ERV is capable of transferring latent (moisture) also. The big advantage to that is it allows the home to retain the humidity difference from the outdoors. My opinion is that everyone could use an ERV for its advantages and built in features.

Condensation collects in most HRVs when warm, moist air contacts the exchanger's surfaces in very cold weather; this can freeze, blocking air flow. Liquid condensation is collected in a condensate pan or carried away by plumbing. Some models transfer water vapor better than others, especially ERVÂs, they don't produce condensation.

Both of these units can have electrical anti-frost heating elements that automatically turn on at about 10 degrees F. In addition to preventing freeze-up, these slightly warm incoming air. Others have a system of dampers that periodically recirculate room air through the unit when temperatures drop below 20 degrees F.

Check to see if your model has a heater, otherwise it could have an internal bypass (such as a Broan unit or, it may have an external bypass, usually field installed. If it does not have any bypasses, usually not found on economically priced units, perhaps a manual one needs to be installed.

I doubt running the furnace fan will have any effect since your unit is most likey self powered and indirectly connected to the furnace (in most cases).

Besides any or proper bypasses your other choice is to manually turn off or install a freezestat control to shut it off in cold weather.

Thanks. It's a Van EE 90 series and per the manual it does run a defrost cycle. The frosting isn't taking place inside the unit. It's taking place in the last 4" of flex pipe that feeds the intake, where it attaches to the unit itself.

If the HRV was installed out of level and the drain was partially blocked, the condensation in the drain pan could backup around the inlet collar. The inlet collar may not be properly sealed, allowing water into the duct. The inlet air at -20C would freeze the water. Just a guess.

Dan Martyn

I am familiar with your unit.
While Dan mentioned the unit must be level, which is very important, the drain pan is on the house side (core location) of intake and exhaust. Sounds like youÂre freezing is happening on the intake from outside?

Is the unit mounted in a warm conditioned space? If not it must be.

It is also imperative that the inner duct is sealed well to collar, the dampers were in the open position and donÂt bind, and most important the outer vapor barrier layer has no holes, tears or penetrations.

Once you checked all that, here is the final cold weather recommendation from the manufacturer:

In a cold region, setup extended defrost by removing jumper JU1F on the circuit board.

zl700 thank you. I spoke with a Van EE distributor today and they echoed what you said so I went digging and found.....

The "tech" that installed the new supply line has it sealed properly where it joins the HRV but simply shoved over the intake pipe going through the wall of the house. Nice. Ice in the intake, ice in the insulated pipe, ice on the sill plate of the house. Guess that the tech didn't feel like going through the trouble of doing it right.

They've got hose#3 on order.

Somone else mentioned that sealing the flex pipe properly at both ends is not enough; the inner core and outer sheathing must both be air tight.

Care to elaborate on that last point?

The inner core is attached to the collars and hoods with large zip ties. Some people (I included) would then use the silver foil HVAC tape (not standard duct tape) to seal even better but more importantly keep the duct from being pulled off.

The outer core (vinyl or metallic) along with the insulation under it should be pulled over the inner connection and up tight to the cabinet or to the exterior wall where the hood penetrates. You can then zip tie this to hold, followed by more tape to seal edges and keep from being pulled loose.

Many skilled installers will cut the inside pipe shorter on both ends so that there is plenty of insulated jacket to pull up to and over the connection joints. Having enough, allows you to scrunch up the insulation up to the cabinet and exterior wall before taping

Thanks for this, I'll be forwarding the info to my home builder to pass on to the "tech" that's trying to solve the problem.

I have a very similar problem. We have a Lennox HRV unit. Just today, we noticed the fresh-air insulated intake duct sagging between the braces that are holding it up between the joists. I poked a hole where the sagging was and out poured water. There were several spots where the duct was sagging, so I drained out all the water with a few cuts to the black plastic wrapper. The water collection started about 10 feet in from the outside and stopped about 10 - 15 feet from the HRV unit itself. The total length of this fresh-air intake duct is about 35 feet.

Have have the exact same problem with my ERV 60H Van EE.

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