I've heard a 'house needs to breath' from at least two old school builders. The argument for it is that the ventilation helps to dry out everything and keep the house healthy. The more modern argument is to seal the house tight and bring in outside air on your own terms.

I was always under the impression that air conditioners bring outside air in and 'condition' it – heat or cool it. That's not true. Air conditioners are closed systems that recycle the inside air over and over. They don't bring in air from the outside on purpose, but due to the pressure created by the air conditioner blower, it does suck air in via leakages. With a tight house, there are fewer leakages from which to accidentally bring in air.

For context on the leakages, most residential building codes require a blower test score of less than 3 ACH50. That means all the air in the house will house will be exchanged 3 times per hour due to leakage, when pressurized to 50 pascals.  Prior to 2009, the threshold was 7 ACH50 (seven times per hour). According to this study, the average score for 100 year old US houses is 22.4 ACH50 to illustrate how far fewer leakages we have now.

Here are some questions I have on my options to bring in fresh air on my terms then in Central Texas.

  • Should I use a ERV, energy recovery ventilator? Are those appropriate for central Texas?
  • Is there a type of add-on or additional feature where mini-splits can bring in outside air – sort of like the 'recirculate' function on a car air conditioner?
  • What about separate, simple mechanical ventilator?

For additional context on how frequently ERV's are actually installed in Texas, I found this comment from an HVAC contractor:

Last year, Tempo installed about 6,000 HVAC systems collectively between its new construction and service/replacement business, and, of those, only three ERVs were installed...

For curiosity, how did the Texas Zero Energy Homes from this list handle ventilation?

  • Preston Haven: Filtered fresh air intake with controller.
  • 5th Street Rehab: ERV.
  • DOE Retrofit: ERV.
  • Green Heights Infill: Balanced ventilation: sensor and timer-controlled central fan with fresh air intake and timered exhaust, MERV 11 filter
  • Drummond House: ERVs.
  • Lost Creek Phoenix: Controlled central fan with fresh air intake and timered exhaust.
  • Malone Cliff: ERV.
  • Brazos River House: ERV, exhaust fan timers, MERV 11 filters.
  • SmartLux: Metered and timed fresh air ventilation system that operates in the metered open position utilizing the fan mode when the system is running, and on a timer when there is a sustained period with no call for conditioned air. In addition, the supplemental desiccant wheel dehumidification system described above maintains an indoor relative humidity of 50% even when the air conditioner is not operating and substantially reduces the latent load on the HVAC system.
  • Village Park: fresh air intake duct with a motorized damper and an electronic controller. All of the bathrooms are tied to an ENERGY STAR-rated central exhaust system with timers in each bathroom. The exhaust fan is tied to the controller so when the unit calls for fresh air, the damper opens and the exhaust fan comes on to accomplish balanced air exchange.

From the above, it looks like an ERV is not the only choice. Mechanical ventilation is well represented. One product I see frequently referenced with this approach is the QuFresh products. These can have a MERV 16 filter. They are less expensive than an ERV. I found this article helpful on the different approaches.

It looks like you can attach fresh air intakes on some mini-splits, but when compared to the QuFresh product, that makes changes based on outside air temperature and humidity, that seems like a coarse approach.