Alaskan winters are long and cold, so here in Fairbanks we build tight houses. In general, tighter houses have lower heating costs, but without adequate ventilation, they can also suffer from excessive humidity and poor indoor air quality. This problem, though usually associated with new construction, is increasingly cropping up in retrofit projects. The Alaska Housing Finance Corporation (AHFC) offers rebates for air-sealing and other energy upgrades, and mandatory before-and-after energy audits performed in the course of the program have found that many upgraded homes are too tight to meet AHFC ventilation requirements.

Meeting the standard calls for mechanical ventilation. In our climate, that means a heat-recovery ventilator (HRV), which pulls in fresh outdoor air while exhausting stale air from indoors. The streams pass, without mixing, through opposite sides of a heat-exchanger core, where up to 70 percent of the heat in the outgoing air is transferred to...

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