Saturday, October 11, 2014

Installing a small Energy Recovery Ventilator for my home

TwinFresh Comfo HRV with remote control
Over the years I have succeeded in tightening up my home using a combination of sealing cracks and interior storm windows that I install in the colder months.  The result is I am not getting enough fresh air in the fall through spring.  It is recommended that interior air be exchanged once every three hours in residential buildings.  One of the indications that I am not getting good enough air exchange is that kitchen smells linger for over six hours after I have cooked a meal.  Lack of adequate ventilation can cause health issues and trap condensation inside the building that can lead to mold and mildew.

I have been researching Energy Recovery Ventilators for some time now and looking for an inexpensive and simple to install unit.  I found a Panasonic unit that would be ideal for new construction but not practical to put in my home.  I found the ideal candidate in the TwinFresh Comfo that is available from Home Depot for under $500.  This clever unit alternates between removing stale air and bringing in fresh air every 70 seconds.  Outgoing air warms a ceramic honeycomb core in the duct that stores heat which is then released as cold air is brought back into the room.  This device claims to be 92% efficient with exterior temperatures at 32°F with an air flow of up to 32CFM.   The fan can also be set to ventilate air in either direction, so I plan to use it as a kitchen fume hood to remove cooking odors since my home did not come with a kitchen vent.

I have posted a web page that the explores the functions and details my installation and ongoing investigations into its performance.  As someone who designs electronic products for a living, I am quite impressed by this extremely well engineered product.  After we have lived with this unit for a while I am considering installing another one in the bedroom to better balance the air flow.  They can be wired to synchronize in reverse so one brings in fresh air while the other removes stale air.

Here is a chart showing temperatures as it operates for 6 minutes with outside temperatures at around freezing:
As you can see the fresh air temperature entering the room averages only a few degrees below the inside ambient temperature.

If you have a home that you have tightened up with DIY interior storm windows and caulking etc., you may want to consider installing one or more of these units instead of installing a large central Heat Recovery Ventilation system.  Even installing three or four of these would still be significantly less expensive than a full-blown ventilation system retrofit.  If you can find someone to do a blower door test on your home and they tell you that your air exchange rate is below .35 ACH (Air Changes per Hour), then some form of heat recovery ventilation would be in order.


  1. Interesting. How tight of a seal do you get with the unit's shutters closed? Or is the intent they will be open most of the time with the air cycling back and forth? Is the unit quiet (perhaps compared to a refrigerator or a bath exhaust fan)? Finally does it really stay below 32F for three months in Maine or do you mean the lows are at least 32F every day for months?

  2. RJ. Here are some answers to your thoughtful questions:

    The shutters do close quite tightly, but I do expect to leave them open through the winter because we really need the fresh air.

    At full speed the fan sound is noticeable from 10 feet, but the lower two speeds are almost inaudible. I would say that it is no louder than a refrigerator with the fan at full speed. It is certainly not obnoxiously loud and much quieter than a 100 CFM bathroom vent. You do notice the "breathing" cycle because the pause between directions is several seconds long.

    Yes, temperatures do remain below freezing for about three months in Maine! We get used to it!

  3. An industry professional commented by email:
    "I have my questions about the real heat recovery. It seems to me, that while the unit is blowing air in, somewhere in the house warm air is being pushed out. Then when the unit is blowing air out, somewhere cold air is coming in. Seems that this would impact the actual heat recovery.
    Food for thought."
    My feeling is that this ERV is designed to address air quality in one specific room - perhaps at the cost of some heat loss elsewhere.

  4. On further review of the manual I have learned that this device can and should be installed in pairs. They can be synchronized through the wiring so that one blows in while the other blows out - balancing the air flow. I plan to install another unit later this year.


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