Laundry exhaust fan ALWAYS On

Recently I have completed several 11 Mo Warranty Inspections in a local neighborhood. Each were single family homes ranging from 2800 sq ft to 4000 sq ft. All had the same builder. In every home, there was an exhaust fan in the laundry room. (Although not required by any local code that I have found, it is a typical find.) In each of these homes, the fan was wired to ALWAYS run, 24-7. There is a switch provided next to the light switch, but does not appear to be connected to the fan itself. I have called out each of these as an inoperable switch, and the fan unable to be shut off except for at the breaker panel witch of course would shut off multiple outlets and lights, etc… After a friendly follow up with one of the clients, they told me the builder said “it is required to have that fan run all the time, by code.” The client took it upon themselves to ask the builder to site the “code” and where they could read it for themselves, and the builder couldn’t answer the question.
So here is the question: Has anyone herd of this? and Should I continue to call this out? I do have a few more inspections in this neighborhood slated for next month. Just looking for opinions on this one.


It isn’t correct ! Call it out.
Question… It it connected to a temperature sensor?

Nope. No sensors, humidistats, etc…

Kevin found the answer.
I wouldn’t like that on all the time.

I don’t like them either, IMO they have advantages but also disadvantages as well.

Provides a negative pressure so it pulls fresh air into the home.
Also supposed to somehow improve the efficiency of a home, at one time they were required in “LEED Certified” homes, and may still be.

Where is it pulling the air from? Is it possible to create a backdraft through furnace or WH vent?
Also by creating a negative pressure in the home, can this also pull more Radon into the home?


Thanks for the videos Kevin! Here’s the thing, both videos indicated a switch to alter the fan’s operation. The homes I inspected had a “dead” switch that didn’t affect the fan at all. Nor did they ramp up when the lights were turned on. Improper wiring possibly or an electrician that has never installed a system like this?

Agree 100%. And not only that you have to hear the sucker running all night.

These houses were anything BUT air tight (could see daylight from basement below the rim joist and one had a passive radon system). My first thought was about the back draft issue with appliances and gas fireplaces, then the radon… Just didn’t seem right.

They might be programmed to stay on or have sensors like Roy mentioned, the sensors are built into the unit and wouldn’t be visible. Do you know if these homes were LEED Certified?

Here’s a real fancy one with sensors.

If you could see daylight from the basement something obviously wasn’t sealed right, around here many builders do install passive Radon systems because it’s much cheaper to install them during construction rather than after.

Here, in NY, there must be a switch/control to override the fan, you may have something similar in your locale:

M1507.3.2 System Controls
The whole-house mechanical ventilation system shall be provided with controls that enable manual override.

Bathroom fan or washroom fan to run all the time is B.S…
If the home is that airtight that it constantly needs outside ventilation, it would be designed with an HRV system.
The other switch should control the fan so the occupants can control the ventilation.


Cheapest way to meet ASHRAE mechanical ventilation requirements. I do mostly energy audits and I see this a lot.


Cheap is the word.
If a house is that tight, that you need to run a little washroom fan all the time to get fresh air, where is it going to come from? You going to leave a window open and how much was the door undercut to provide a negative pressure to suck air in.
Fan should be on the light switch or have it’s independent switch. Or even better have a window and have all the air you want. LOL
I would have to see some documentation that the fan meets ASHRAE requirements and where it says they have to run all the time. I know I would not want to listen to that all day.

It does not matter what we feel about it, it’s prescribed in the code, two ways to go about it: continuous or intermittent, pick one. Read:
M1505.4.3 Mechanical Ventilation Rate

My house has an April Air system tied directly to the return air duct at the furnace, For 6 minutes every hour (weather permitting ) the system turns on and pumps outside air directly into the existing ductwork that delivers it throughout the home. I thought I was going to hate this thing and would be unplugging it upon move in but it turns out it’s great !

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Guess I’m confused. Are we discussing a ventilator in a laundry room, or whole house ventilators, bathroom ventilators, passive radon or what?

Missing the point on why a standard bathroom ventilator, installed in a laundry room or closet, should be in a continual “on” mode. Never have seen one installed in that location and scratching my head on some of the replies. Just trying to learn I guess.

A laundry room does not require ventilator per se. In new, air-tight house construction, when there are not enough air exchanges per hour in the house… extra, what’s referred to as a whole-house ventilation, is required to bring in fresh air from the outside. There are several ways to accomplish this as allowed per prescribed model codes. One such way is the use of a fan installed in a laundry room as stated by OP. Look, carefully, through every single reply and it should make sense :slight_smile: