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Community and Q&A

Taking Advantage of Temperature Differences

Timothy Byers | Posted in General Questions on

Our 1947 one story house is in Southern California in building zone 3B. It is hot and dry during the summer but cools down quickly when the sun goes down. Also, there are many days during the other three seasons where it is cold at night but warms up fairly quickly in the morning.

Our gas furnace is located in a closet with a 12.5” X 29” combustion air vent in the exterior wall that allows for free exchange of air with the outside. We are planning to replace the gas furnace with a heat pump. I would like to take advantage of the temperature difference between inside and out to draw outside air into the return air plenum to provide a bit of heating or cooling and at the same time bring fresh, filtered air in to ventilate the house.

Such a system would address security concerns of leaving windows open at night as well as filter out the wildfire smoke and pollution from a nearby expressway.

Is it possible to use an economizer (such as the AirScape Residential Economizer) or a Central Fan Integrated Ventilation system to accomplish this? Any other possibilities?

Could we repurpose the combustion air vent to provide the outside air?

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  1. Steve Knapp CZ 3A Georgia | | #1


    Have you considered installing an ERV (Panasonic and Broan make balanced units)? The AirScape alone is almost $1,000. That's pretty close to the cost for a typical ERV.

  2. Timothy Byers | | #2

    An ERV would accomplish the ventilation piece. But, say it is still hot inside the house after the sun goes down and I want to bring in some of that lovely cool, dry air in from outside. Won’t a running ERV act to transfer heat from the exhaust air to the incoming air in a way that is contrary to my goal of cooling?

    I don’t think the airflow of a typical HRV, ERV, or Central Fan Integrated Ventilation system is adequate to accomplish much, but I get the sense that the airflow of the economizer is much greater. One thing I hope to get from this query is advice on whether this strategy of cooling or heating the house by capitalizing on the temperature difference of outside air (even if it is not a large amount) is realistic. Cost is not the most important consideration if it is a good long term investment.

  3. Steve Knapp CZ 3A Georgia | | #3

    An HRV will temper the air during the exchange process. An ERV will transfer moisture to the drier air stream. But I think you are right that neither of these systems will quickly flush the hot interior air. (A window fan or whole house fan would probably work better.)

    Whether the Airscape would serve will likely depend on the size of the air handler on your new heat pump system.

    Maybe one of the HVAC experts will comment.

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