ERV or HRV in Northern Virginia

[kcb203]

I relied on advice from this forum several years ago when replacing my furnace/AC in a 60-year-old house with a Carrier Infinity system.

I'm about to build a new home in Northern Virginia. I've already specified to the builder that I want two zoned Carrier Infinity systems, one unit divided into zones for basement and first floor, and another unit with three zones for 2nd floor, master bedroom, and finished attic.

In my old, poorly insulated/sealed house, we needed a humidifier in the winter. Based on my research, a tight new house often has the opposite problem of high humidity, even in the winter.

I'd like to use an HRV or ERV for fresh air, but I'm confused about what's needed in my climate. For an older house, it seems as though an ERV would be better in winter to keep indoor humidity higher, but perhaps a tighter house would need an HRV to keep winter humidity lower? An ERV is obviously preferable for summer.

What should I specify? Or should I go a year without a humidifier or HRV/ERV and see whether humidity is too high or too low in the winter, and then choose?

[buddylee]

You fall into zone C which includes areas as far north as Harrisburg, which recommends you go with an ERV. I highly recomend them in many new homes as they continue to get tighter. But they can always be added down the road for a little extra cost, so way your options and see whats best for you.

[teddy bear]

I a humidifier in the winter. Based on my research, a tight new house often has the opposite problem of high humidity, even in the winter.

I'd like to use an HRV or ERV for fresh air, but I'm confused about what's needed in my climate. For an older house, it seems as though an ERV would be better in winter to keep indoor humidity higher, but perhaps a tighter house would need an HRV to keep winter humidity lower? An ERV is obviously preferable for summer.

What should I specify? Or should I go a year without a humidifier or HRV/ERV and see whether humidity is too high or too low in the winter, and then choose?

I see the merit of the wait and see idea. It is a way to tell how your moisture generating ability matches your the natural dry air infiltration rate. If the home is dry enough to avoid window condensation, usually mechanical ventilation is not need during cold weather. The pressures on a home vary dramatically from cold, windy winter compared to windless, warm weather. Even leaky homes need supplemental mechanical fresh air ventilation during summer. Ashrae suggests 7.5 cfm per occupant and .01 cfm per sqft. Of house to supplement natural leakage. This is critical during the warm weather, window closed time of the year. Fresh air ventilation is required to purge the home of indoor pollutants and renewing oxygen when occupied. Another consideration is the make-up air for the bath fans, clothes drier, kitchen hood, and fireplaces/water heaters. Maintaining <50%RH to avoid mold/dust mites growth is also critical. With the moisture from 75 cfm of fresh air during warm weather plus normal 3-4 occupants and moisture diffusion, expect up to a 100,000 btus of latent load per day (90 pint/day). On hot days, your long running a/c will maintain <50%RH while cooling your home. During rainy cool weather (no a/c load), you need up to 90 pints of dehumidification/day. A ventilating dehumidifier is an alternative method to provide make-up air ventilation throughout the year along with humidity control. An ERV reduces the summer humidity load 30-50% provided you exhaust an equal amount of <50% RH air. Exhausting humid air humidifies fresh being brought in through the ERV. Exhaust devices depressurize the home sucking in additional humid air. Basements add additional moisture to the home. Adding a good vapor barrier to the outside of the masonry components decrease the diffusing outside moisture. With an ERV, the supplemental dehumidification is reduced to 65-75 pints/day. In most cases, mild climates do not justify the ERV in addition to the whole house dehumidifier. Many brands of whole house dehus are avialable. Regards, Dehu TB