Monday, July 3, 2017

Why Is My Exhaust Fan Always Running – Explaining Continuous Operation

You hear it across the country – Who left the light on? Who left the door open? Maybe even Who left the bathroom exhaust fan on? While there are no good reasons for leaving lights on and doors open and the guilty party should be identified and properly reprimanded for their crime, leaving the bathroom exhaust fan on might not be as straight an answer as you think.

In recent years homes have been built to tighter standards that reduce the energy usage of the homes. These tighter standards allow the home to maintain a comfortable living environment using the least amount of energy possible. Unfortunately a side effect of these tighter standards is that the indoor air quality can suffer. This is where a continuously operating exhaust fan comes in (also known as Mechanical Ventilation). A continuously operating exhaust fan provides a way to exhaust the stale air that builds up inside a home. The fans airflow rate is set to achieve the number of air exchanges needed for your specific home.

There are many options for continuous operation exhaust fans but there are basically three locations for them:
A dual speed exhaust fan in the bathroom: This will operate continuously at a low speed then have a high speed for when the bathroom is in use.

A centrally located exhaust fan: This might be in a main living area open to the rest of the house.

A kitchen range hood: This operates much like the dual speed exhaust fan in the bathroom. A low speed provides the continuous operation while the higher speeds provide the needed ventilation when the kitchen is in use.

A prerequisite for a continuously operating exhaust fan is that it is quiet. With it always on, it is very important that the sound level does not interfere with everyday life. Most continuously operating exhaust fans will have a sound level that is barely noticeable.

It makes sense – bad air out, good air in, but there are still some questions that arise:
How much energy and money is this going to cost me? A very valid question. Energy costs and usage are definitely hot topics, but when you do the math, the exhaust fan is using very little of each. There are a few factors that go into calculating the costs. The two big ones are what type of exhaust fan you have installed and what your actual electric rate is. Using the average United States electric rate with an ENERGY STAR® certified exhaust fan, the cost will be approximately $.60 to $1.50 per month. Overall, a very small price to pay to ensure the quality of the air you breath.

That cant be good for the fan if it is running all the time?
Not to worry, fans that are meant for continuous operation have been tested and certified for this type of usage.

Can I turn the fan off?
The effectiveness of the system to provide proper Indoor Air Quality is based on it operating continuously so it is recommended that the fan stay on. However, there may be times when the fan needs to be turned off for servicing. Some units will be installed with an override switch while other units will need to be turned off at the service panel. You should contact your builder/installer for the specific details of your installation.

So the next time you are tempted to blame someone for not turning the exhaust fan off, stop and think that you might actually want to thank them for keeping it running and ensuring the quality of the air you are breathing. To learn more about Indoor Air Quality, ASHRAE 62.2 standards and Air King products that comply, visit


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  3. TY. I will stop yelling at my builder....

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  5. Wont it suck the heat out of the room?

    1. There is a balance between bringing fresh air in and exhausting the conditioned air of the room (cool or warm). With continuous ventilation, it operates at low levels so while you will be "losing" some conditioned air, it is kept to a minimum and should not cause major stress on your HVAC system.

    2. What about when you heat just the bathroom with electric baseboard and have the door closed. Balance of house heated with wood stove. Heat is being exhausted out continually and heater is always running.

  6. You are exhausting (potentially stale) conditioned air - I get it. But where is the 'fresh' air coming from? The cracks around the doors, backflow through the other vents (dryer, range hood, etc)? AND, this air coming in is unfiltered.

  7. seems like this should be built into the heating/cooling system and only operate when the heater/cooler isn't.

  8. At 40 CFM it would exhaust over 21 million cubic of conditioned air.

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  10. This information is amazing. You guys understand your users!!!