Are Powered Attic Ventilators Ever a Good Idea?

It's time to delve into an important topic - powered attic ventilators. Over the years, I've shared my thoughts on this subject and received a tremendous response from readers. Today, I want to explore the...

It's time to delve into an important topic - powered attic ventilators. Over the years, I've shared my thoughts on this subject and received a tremendous response from readers. Today, I want to explore the question of whether there is any situation where a powered attic ventilator might be justified.

Recap of Powered Attic Ventilator Problems

Before we discuss the potential benefits of powered attic ventilators, let's briefly recap the problems associated with them:

  1. They pull air from anywhere, including conditioned air from the house, which means they cool the attic using your air conditioner.
  2. They can draw in moist, moldy air from basements or crawlspaces, compromising the air quality in your home.
  3. They can cause backdrafting in water heaters, furnaces, or boilers, leading to incomplete combustion and the presence of harmful carbon monoxide.
  4. They address the wrong problem - the heat that enters the attic happens due to radiant heating, which cannot be resolved by using a fan.

And if you're looking to save money on your cooling bill, powered attic ventilators won't be of much help either.

Questions from Readers

While my previous articles on this topic are closed for comments, I still receive questions from readers via email and the contact form on my website. Let's address a few of these questions:

Question 1: "The installers of my new HVAC system suggested installing a thermostatically controlled exhaust fan to protect the air handler from excessive heat. What do you think about this?"

The reality is that a powered attic ventilator won't significantly extend the life of your air conditioner. Instead, if you're concerned about attic heat affecting your air conditioner, it's better to focus on reducing the radiant heat by using a radiant barrier above the unit. Powered attic ventilators don't effectively address radiant heat and will only marginally lower the attic air temperature, leaving the air around your AC still hot.

Question 2: "What if I install a second gable fan at the opposite end of the house to balance the air flow?"

While balancing the airflow in the attic may seem like a good idea, it's not foolproof. Even if both fans move equal amounts of air into and out of the attic, there's still a chance that the exhaust fan draws air from the house while the supply fan pushes hot attic air inside. Moreover, more fans mean increased electricity usage.

Question 3: "We don't have AC, and our house gets hotter in the evening. Would installing multiple attic fans help in our situation?"

In your case, what you really need is a whole-house fan that flushes out the hot air from the house and brings in cooler outdoor air. A powered attic ventilator won't serve this purpose effectively. Investing in a whole-house fan, like the air-sealed, insulated one by Tamarack, will not only cool your house but also prevent heat loss in winter.

Air-sealed, insulated whole-house fan by Tamarack Air-sealed, insulated whole-house fan by Tamarack

Question 4: "Hot air is pouring out of the soffit vents even before summer. Can installing attic ventilation fans solve this?"

Having a hot attic is not necessarily a problem, as long as it doesn't affect your living space or cooling equipment. If you're experiencing heat transfer from the attic to your home, it's essential to focus on air-sealing and insulating the attic properly. This also applies to poorly sealed and insulated ducts. Powered attic ventilators won't provide an effective solution to these issues.

Question 5: "I'm confused about whether too much insulation in the attic is a bad thing. Should I install an attic fan or add more insulation?"

For your situation, it's best to avoid installing a powered attic ventilator. In fact, passive attic ventilation doesn't offer significant benefits either. Instead, focus on proper air-sealing and insulation techniques to reduce heat transfer. Investing in a powered attic ventilator won't address the underlying issues effectively.

Is It Ever Helpful to Use a Powered Attic Ventilator?

Let me start by acknowledging that powered attic ventilators can be helpful in one specific scenario. If you don't have air conditioning or natural-draft combustion appliances, a powered attic ventilator can help keep your attic cooler. For instance, I once knew someone who installed a ventilator to prevent the rubber handles on their wheelchair from melting.

However, when it comes to cooling the house, powered attic ventilators are not the ideal solution. To justify their use, you would need a situation where:

  • The house doesn't rely on air conditioning, or the AC is turned off when the attic ventilator is running.
  • The house doesn't have any natural-draft water heaters, furnaces, or boilers.

If you don't have air conditioning, why not consider using a whole-house fan to cool your home instead of attempting to cool the attic? While I continually review readers' questions in hopes of finding a scenario where powered attic ventilators are the best option, I have yet to come across such a case.

Allison Bailes, based in Atlanta, Georgia, is a respected building science consultant, speaker, writer, and founder of Energy Vanguard. With a Ph.D. in physics, Allison shares his expertise through the Energy Vanguard Blog and is currently working on a book on building science. Follow him on Twitter at @EnergyVanguard.