Q: Why has our new heat recovery ventilator (HRV) given my husband and I nasal problems and nose bleeds? Following your recommendation we were thrilled that our new HRV did away with the condensation on our windows, but even running several humidifiers hasn’t helped our noses.
A: The drying power of a properly functioning HRV in winter is very strong. It sounds like your home is too dry for comfort because your HRV is being running more intensely than it should be. Try reducing the HRV fan speed or shutting off the unit during the day or night. Think of the HRV and your humidifiers as working opposite to each other. The ideal HRV operation level results in a reasonable level of humidity and comfort while also being dry enough to prevent running window condensation. And the colder it gets outside, the more of a compromise you need to maintain between your noses and the windows. That’s because the colder the outdoor air, the drier it will be when the HRV sucks it in and warms it up. Also, the colder it is outside, the more condensation will want to develop on the glass.
As long as beads of condensation aren’t running down the inside face of the glass of your windows you’re okay. A little condensation around the edges is fine if that’s what’s needed to keep your noses happy. Don’t drive relative humidity in your home down below 35% to 40%, but don’t try to keep it higher by running humidifiers. Just throttle back the HRV. Running a humidifier at the same time as an HRV is like pressing the gas pedal and brake on your car at the same time.
The unfortunate fact is that most windows today aren’t insulative enough to eliminate all condensation during cold weather while also having indoor humidity levels high enough to be completely comfortable for all people all the time. For almost every home in a serious heating climate, you’ll need to tolerate a bit of window condensation while also tolerating somewhat drier conditions than ideal for comfort. It sounds like the balance of your house can be shifted somewhat towards more moisture because of your dry air issue, but you should expect complete and perfect comfort, either. Windows just aren’t that good yet.