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Your Bath Fan Sucks, And That's Not Good Enough

Energy recovery ventilators (ERV) replace kitchen and bath exhaust air with clean and tempered supply air
December 06, 2021

Traditional bathroom ventilation fans depressurize your home, causing leaks somewhere else in the house. Those leaks bring cold, wet, and stinky air into your home, where it causes IAQ and energy bill problems.

Heat recovery ventilators transfer heat between incoming and outgoing air; energy recovery ventilators transfer moisture and heat. Using an ERV for bathroom ventilation adds balanced ventilation to a house that brings filtered, tempered air into the living space.

When you remove air from a room, it must be replaced because we do not live in a vacuum.

Leaky houses leak more easily

In regular old leaky houses, the air is replaced through gaps, cracks, and holes from places like crawlspaces, garages, attics, and wall cavities where pollutants can be sucked into the living space.

Common pollutants:

  • Moisture
  • Radon and soli gasses
  • Gasoline, carbon monoxide, or other garage fumes
  • Dead mice, squirrels, and others
  • Dust and dirt

Tight houses leak less

In a tightly-built house, like any house that @JakeBruton builds, it is more difficult for the replacement air to slip in from all of the usual places. If the fan were big enough, it could break the walls and let air in that way, but because even the strongest bath fans cannot do that, the fan can only fan suck less, and that sucks.

That's why Jake uses energy recovery ventilators (ERV) in his tightly-built houses.


Some people call them "enthalpy recovery ventilators," because it is technically more accurate. But I reject that terminology.

Nobody knows what enthalpy means except people who already know that energy recovery ventilators manage moisture and heat. Because building high-performance houses is already difficult enough for traditional builders to embrace, further complicating things with more confusing names that only eggheads care about, is bad for the industry.

How an ERV works

A simple conceptual sketch is to picture two bath fans at either end of the house. One sucks air out of a bathroom, and the other sucks air into the living room.

The problem is that this would suck untempered, unfiltered air into the living space. Conversely, the bath fan removes warm air from the house, and cold air would also get sucked in from the other fan in winter.

ERVs (and HRVs) have a core inside the box where the airstreams cross through each other, separated by a membrane. Incoming air and outgoing air do not mix, but they can transfer heat and moisture to keep through the membrane to keep interior-air stable. There are also filters attached to the incoming air to clean it before entering the box.

You can operate ERVs with wall switches, a timer, or both. By intermittently operating, regardless of bathroom use, you can keep the air inside the house fresh and clean.

More ventilation info to explore:

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