Q We have in-floor heat and double-pane, energy-efficient windows in our house. If we run the air-to-air, the air in the house becomes extremely dry. So we've started running a small humidifier. Is there a better way to make all this work? In other words, since we don't have a furnace, how do we keep the humidity at 30 to 35 percent, have air-to-air operate, have heat and not use all this energy?
A The "air-to-air" you mention is a whole-house ventilation system. This type of system is important to ensure good air quality and it's code for most homes built in Minnesota since 2001. Excess moisture should be considered a pollutant.
However, an HRV, a heat recovery ventilator, is one type of ventilation system. It can cause excessive dryness if not properly sized or adjusted for your home. Even with proper ventilation, an HRV can make your house excessively dry. That is why experts recommend ERVs (energy recovery ventilation systems) as a more appropriate device for whole-house ventilation.
Although both HRVs and ERVs capture thermal energy, ERVs transfer a high percentage of the water vapor to the air stream with the least amount of moisture. That means an ERV "kicks out" some of the incoming moisture in summer, keeping your home more comfortable, and retains some humidity in winter, again providing more comfort. Because ERVs generally cost more than HRVs, the latter are used more often. Contractors, in an effort to keep costs lower, tend to install HRVs when an ERV would provide better comfort and greater efficiency by reducing the air-conditioning load and eliminating or reducing the need for humidifiers.
Now for your problem. If your house is properly ventilated, then running the humidifier is the right thing to do. You may also need a dehumidifier in the summer.
You need a minimum amount of air flow through the ventilation system for acceptable air quality. When you have your heating system cleaned and tuned, have the contractor measure and balance air flow through your home; if a reduction in flow is possible, the humidity may rise a bit.
HRVs have a life expectancy of about 15 years. When the time comes to replace the HRV, consider getting an ERV.
Remember, you need to run your ventilation system year-round, whenever your house is closed and occupied.
