Can You Ventilate a Home with Attic Air?

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I've seen some crazy things done to homes. It's usually someone's attempt to make things better. Sometimes that someone is a homeowner or other occupant. Sometimes it's a contractor. But it always seems to be a solution to a problem that creates other problems. It's just like they say: Our biggest problem is solutions. So what's the problem with this method of ventilating a home?

One of the home energy raters we work with in the Atlanta area, Bruce Kitchell, sent me these annotated photos. He found an air handler for a heat pump in an unconditioned attic. The return plenum had a filter sitting on top of it, as you can see above. The filter was there to filter the "fresh" air they were using to ventilate the home.

Beneath the filter was a hole cut through the fiberglass ductboard plenum. When the system runs, it pulls return air from the conditioned space in the home and it also pulls a significant amount of air from the vented attic.

Hey, fresh air is good, right? And this ventilation system is about the cheapest you can install. All you need is a box cutter and a one dollar filter.

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Let's take a look at the problems with this solution.

Indoor air quality. Attic air isn't the cleanest air around. It's got lots of dust and dirt, probably a fair amount critter poop, and maybe even some dead critters. That little filter isn't going to stop everything. That little filter probably also has some significant bypass around the edges so not all of the "fresh" air goes through the filter.

Comfort. That hole in the return plenum is going to suck in a lot of attic air. The air conditioner certainly wasn't designed to handle a lot of 120° F air being mixed in with the return air. I wouldn't be surprised if they have trouble getting the house as comfortable as it should be.

Operating cost. That hole pulls in a whole lot of air, I'm sure. It's hot and humid in the summer. It's cold in the winter. Their heating and conditioning systems will run overtime in an attempt to heat, cool, and dehumidify that air. What they saved on putting in a proper ventilation system will quickly be eaten up by high electricity bills. According to Kitchell, the most recent occupants renting this home moved out because of huge electric bills. Not too surprising.

Critters. Any HVAC tech who's been on the job for a while can tell you about the dead animals they've found in HVAC systems. Check out HVAC Hacks and Other Screwups for some photos, if you have the stomach for it. Snakes, squirrels, raccoons, birds. If they can get in your attic, how hard do you think it would be for them to get past that filter?

Get the picture?

An interesting bit of irony here is that they covered the plenum with mastic to seal it tight before cutting that hole. Nice!

Ventilation is a good thing. We want airtight homes and a good system to bring in outdoor air. And yes, it's certainly possible to use the return plenum to bring in your ventilation air. But it needs to come in from outdoors, not the attic. And it needs controls and dampers and critter screens. The AirCycler system is one that can do that properly.

Ventilating a home with attic air as in the photos shown above isn't such a great idea after all. It's a solution that creates a whole host of new problems.

And speaking of solutions, did you know that, in the chemical sense, whisky is a solution? So I guess that's an exception to the rule about solutions being a big cause of problems! Oh, wait. I think I remember a time or two that it caused me problems.

 

Related Articles

Can You Cool Your Home with Crawl Space Air?

What's That Ice Chest Doing in This Attic Duct System?

Insulation to Go - Creativity in the Attic

 

Photos by Bruce Kitchell of Airedale Energy Consultants in Marietta, Georgia. Used with permission.

 

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Comments

Chris Brown

I would say that now I have seen it all, but then again......

John Proctor

Allison -- This is an example of the principle that there are many more bad ways to do things than there are good ways. You might add a link to one of your posts that talks about the extremely good principle of sealing the plane between the conditioned space and the attic.

Dan Geist

You forgot to mention the fact that the cuts on the ductboard itself will likely shed fiberglass particles into the home. Thankfully there's a a filter on the air handler's intake that'll take care of 100% of those, right?

Steve Waclo

Following up on Chris' observation, "Come and get me lord, I've seen it all."

Here in the dry desert of Northern Nevada, where cooling season diurnal temperatures can swing 50F (!!), I use a turbine fan to pull home air into the attic after midnight, with micro-screened open windows providing relief air, and am able to pull inside temps to near outside ambient by morning. My wife is not thrilled waking to 68F but that rises by early afternoon and tops out around 80F in early evening. Did I mention 10% RH?

I would luv to have been a fly on the wall when Bruce gently inquired of the home owner where the "hole in the return" concept came from. 😄

Cameron Taylor

Not a solution that Bill Ding would approve, that's for certain! 😊

Worth noting is that this attic air intake will pressurize the house like a balloon. So not only are they creating extra work at the air handler with the attic air, a good amount of inadequately conditioned air will be pushed right back outside through the envelope. It's lose lose.

Kris

IMO the real travesty is the choice of filter. I would have paid the extra $5 and bought a high efficiency filter from Home Depot. *sarcasm* :)

Ray Austin

Whiskey as a solution followed by I 'remember'?

Allison, I think you are doing it wrong. Whiskey is intended as a magical liquid that makes you forget, not remember.

Yeah I was thinking we would just forget this fresh air dilemma and just go off and get bombed somewhere.

Anyone?

Let's face it, you come across one of these and you're going to wish you were bombed. LOL.

Jack

Allison: this article makes good sense to me, but will you please clarify one thing?

If the attic in the article were a sealed attic (e.g., open-cell foam on roofline) rather than a ventilated attic, then the strategy of adding a return on the plenum in the attic would be exactly what Joe Lstiburek recommends in his "cool hand Luke" article, correct?

I am located in the hot and humid south and recently sealed my attic. After doing so, I found high humidity in the attic and responded by adding supply air which seems to have corrected the problem. I am now planning to add a small return grill to the ceiling of the central return closet (air handler location) to finish the job. In other words, I am planning to do the exact thing that you pillory in this article! Can you confirm that adding a return to the air handler is NOT a bad idea when the attic is *sealed*? Thanks!

Allison Bailes

Jack, you are correct. Adding a little bit of supply air and putting a return in the attic will condition the space and minimize the possibility of moisture problems. That's what Joe was talking about in the Cool Hand Luke article. But recall he said it's against code. Putting smoke detectors in the duct system so that it shuts down if there's a fire is done commercially to overcome the problem, so that's one way to do it while reducing the risks.

Jack

Great, thanks for confirming!

I have 2 related questions that I have not been able to find referenced on your blog or elsewhere: First, where should the attic return be physically located? I have a central return on the air handler in my 1960s home. Currently I have an attic return (just a grille in the ceiling) at one of the ends of my ranch home. But I can smell and feel the more humid attic return air flowing into the end room (no door) as it flows to the central return. I'm considering putting the return grille in the ceiling of the central return closet instead. Good idea?

Second, what should be done in the winter with the attic supply and return? The air handler will no longer dehumidify the attic air because it is in heating mode, not AC. Of course, the attic air should not need to be dehumidified in the winter. Will the attic supply, blowing in warm air, cause potential problems with condensation on the roof deck since the roof deck will probably be colder than the attic air? In short, should the attic supply and return be *disabled* (sealed) in the winter?

Thanks again - I have leared a LOT from your blog!