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Community and Q&A

Supply-Only Ventilation System

jbrandt | Posted in Mechanicals on

We are building a home in North Texas, climate zone 3A. We are in a rural area and are limited in contractors who will work our area.

We have decided on a Mitsubishi SUZ-KA30NAHZ paired with a ducted SVZ­KP30NA air handler. Contractor wanted to install a powered damper with ventilation controller, ducted into the air handler return. The problem I have with that setup is that the air handler is variable speed and fresh air CFM through the damper will vary based upon the speed of the fan at the time.  I suppose we could set the damper schedule based on the middle fan speed and just be a little over or under ventilated as the fan ramps up and down, but I’d prefer a little more precision.

The contractor suggested an ERV if I wanted more control over ventilation, which I don’t believe is the best solution in our climate.  I’d opt for a dehumidifier with ventilation before the ERV, but would prefer to try a simpler, less expensive alternative first. Our house only requires 38 CFM of ventilation. I’d consider the small Panasonic WhisperComfort ERV, but while it exhausts 40 cfm, it only supplies 30 CFM. I’d prefer positive pressure or at least a truly balanced system.

My thought is to install a powered damper with its own fan (Aprilaire 8142) and not duct directly to the HVAC return. Rather, the fresh air supply would vent into the living room right next to an HVAC return register, which would take up much, if not all of the fresh air and distribute throughout the house. By not being ducted directly into the HVAC return, the airflow wouldn’t be as affected by whatever speed the air handler fan was running.

I realize not all of the fresh air would make it into the return and would instead remain in the room, affecting the temperature and humidity of the space. My hope is that this would be a small amount and would balance out without comfort issues.

Has anyone employed the strategy of dumping fresh air near an HVAC return for this purpose in a similar climate? Just wondering how it impacted comfort in the room. I believe I have read about it being done with ductless mini splits.

Thanks for any input.

– Jack

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  1. brendanalbano | | #1

    AirCycler is a product that balances a supply air damper connected to your air handler with an automatically controlled bath fan for balanced ventilation. The AirCycler website claims it can accommodate variable speed blowers, so it might be worth doing some research into how that works:

    I don't know if this is the best approach for your climate zone, but I just thought I'd mention it in case it was a useful option!

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