There's a safety recall on Venmar HRV's. They can overheat and cause a fire. Go to
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for model and serial numbers of faulty ones. We had a house fire close by that was caused by one of these over-heating. From what I understand, they are sending homeowners an add-on kit to detect an overload, but this is second hand news. They're closed for Christmas, but I'll call their 1-800 hot line for further info. In the meantime, unplug it if you have one.