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Indoor Fresh

We made our house more airtight and efficient, but the air does not seem fresh or healthy. Would installing an efficient fresh air window ventilator help or do we need a whole-house model?—Joyce B.

One drawback to making a house more energy efficient is that indoor air quality may suffer. An airtight home can result in a “stale air” feeling. On the other hand, an airtight home allows for better control of humidity, dust, allergens, etc., so it is still better overall.

There are many methods to improve the indoor air quality without resorting to just opening a window once in a while. Opening a window for a short time might not lose a huge amount of heat; the key is a very short period and a lot of air movement, such as on a windy day.

The efficient window fresh air ventilation units are very effective. I use one in my home office. Larger whole-house ducted models are more effective, but with the furnace blower set for continuous air circulation, my window unit eliminates staleness throughout my home.

These fresh air ventilation systems are called heat recovery ventilators (HRV). There is a heat exchanger built into the unit. As the stale heated air is exhausted outdoors, it passes through the heat exchanger first. There it transfers much of its heat energy to the incoming cold fresh air so your energy dollars are not lost.

During the summer, the outgoing cooled stale air pre-cools the incoming hot outdoor air. All the HRV models have effective air filters to clean the air before it enters your home. If you have a problem remembering to change filters, select a model that has an indicator light to alert you when it is time to change the filter.

The window units look similar to a typical window air conditioner, but they weigh less because there is no heavy compressor. They have multiple speeds and are quiet on the low setting, so they work well for bringing fresh air into a bedroom while you sleep. The best ones use a super-efficient direct current (DC) type motor and use only about as much electricity as a light bulb.

A whole-house HRV model is usually mounted in the utility room, attic, or basement near the furnace. It can be connected to your existing furnace duct system, but it is best to install its own ducting. The stale air inlets are often located in the kitchen and bathrooms and the fresh air outlets can be in a bedroom, living room, or hallway.

A variation on an HRV is an ERV (energy recovery ventilator). An ERV also transfers the moisture between the outgoing stale air and the incoming fresh air along with the heat. This can help keep the indoor air from becoming too dry during the winter and too humid during the summer. By maintaining the proper humidity level, you can lower the thermostat in winter and raise it in summer for a utility bill saving without sacrificing comfort. ERVs are most popular in warm, humid climates.

There are several designs for the heat exchangers (crossflow, rotary, heat pipe, etc.) used by the various HRV/ERV manufacturers and they all are effective. Rotary designs are particularly effective for areas with higher summertime humidity.

When selecting an HRV/ERV unit, consider the types of controls. Multiple speed settings are a definite plus. This feature allows you to adjust the speed for quicker ventilation, but with more noise, or a quieter slower speed for sleeping or continuous use.

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