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Community and Q&A

ERV for a basement apartment

Yaakov Weintraub | Posted in GBA Pro Help on

We are renovating a 900 sq. foot basement apartment in Beacon, NY (Hudson Valley – area code 12508). It’s partly below grade, and pretty tight with new double pane windows.

We’re thinking of putting in an ERV for ventilation since:
1) We think that having the availability of ventilation in the basement apartment is a good thing.
2) We’ve noticed a slight mustiness in there.

We just got the house and need to do the reno pretty quickly, so can’t take things like RH across multiple seasons. We could test for air tightness, but it seems pretty tight upon inspection by our contractor.

We’re leaning toward the ERV because:
1) There will be some energy savings (though from what I’ve read not a very big amount)
2) It seems to give a more conditioned air coming in than plain ventilation (e.g. somewhat warmer air in winter and cooler in summer than with straight ventilation).

We’ll probably add some dehumidification with a portable unit if it turns out to be needed (the previous occupants said they did that in the summer, and that was all they needed – no AC). We may be able to hook it up to a drain to eliminate the need to empty the unit.

Any thoughts on the above?

How would the above compare to having a ventilating dehumidifier? I’m concerned that would bring in cold air in winter, hot air in summer when ventilating.

Pros/cons of each approach?

Thanks very much in advance,

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  1. GBA Editor
    Martin Holladay | | #1

    Ventilation and dehumidification are two different operations. If you operate a ventilation system during cold weather, the ventilation air will help reduce indoor humidity. If you operate a ventilation system during hot, humid weather, the outdoor air will raise the indoor humidity level and increase the load on your dehumidifier. So if you suspect that your basement is damp, you should be careful not to overventilate during the summer.

    Ventilation needs for a 900-square-foot apartment will be quite low. If you go ahead with your plan to install an ERV, make sure that you verify the exhaust and supply airflow rates -- in other words, make sure that you commission the system -- so that you know your ventilation rate and adjust it to the level you want.

    For more information, see Designing a Good Ventilation System.

  2. Yaakov Weintraub | | #2

    Thank you. The ERV we are considering has a fairly wide range of adjustments on both exhaust and supply airflow, and we can use those to commission the system. That's one reason we chose it. The guidelines on this seem to be difficult to figure out - there are standards, but they're not necessarily the best choice. The ventilation apparently depends a lot on the level of contaminants in the home. For a low emission home, it makes sense to follow or under-ventilate compared to the standards, while for a high emission home, it makes sense to over-ventilate compared to the standards. Is there an easy way to determine if this is a low-emission, or high-emission? I know that we are using low-emission products in all the renovation (e.g. no-formaldehyde flooring and zero VOC paint and finishes), but there is also pre-existing construction in there.

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