I have a coat closet, 6' X 2' X 8'. I am going to place my AV rack in there. It gets hot in there in the summer (cold in winter). I need to vent it. Quiet fart fan from home depot with a few feet of flex duct and vent into garage attic is my least expensive option. Good enough? Or should I spring for the ATM System 1? Has anyone used the Cool Components inline fan solution?

You should look at the information on ATM's site, and at Cool Components, about ventilation to get some ideas as to what you'll be wanting to do.

As for "garage attic," it depends on prevailing winds (believe it or not; you don't want attic air pushing past the fan and into the closet as attic air sometimes smells musty), attic vents, how you build the rack as regards moving air at different levels inside the rack....

If the closet is otherwise tightly sealed, venting to the attic won't accomplish much (very little flow). And, venting into the attic will probably increase heating and cooling costs for the house because this scheme will discard conditioned air.

What is your heat load in the closet?

The options recommended by ATM and MA and Cool Components all seem to move as much CFM as the advertised flow of some of the fans at Home Depot designated for "large" rooms. CFM is CFM regardless of heat load. I have not calculated it so I cannot say exactly. Your basic 5.1 setup and network gear that is always on. Rack is open.... no sides/doors. Closet would pull replacement air from the standard gap under the door. I could put a vent panel in if I need to.

The fan can be vented to atmosphere if necessary. I can either tie into existing trunk from another exhaust fan or duct to the existing attic exterior vent location.

My main question was basically if there is any tangible benefit of using something 5-6 times the cost of the cheap solution. If CFM is the key, it seems that any option that provides the appropriate air movement would serve the purpose. Fan noise is the only concern in the back of my mind. Obviously an in line fan can be located away from hearing range. But some of the better box fans are probably quiet enough. Except at night, the ambient noise level in my house would make the fan noise a non-issue honestly, so probably not as big a deal as it could be.

When I am motivated, I could calculate the heat load of the rack, but my guess is that is within the range that would be addressed by the recommended solutions from ATM, and others.

I've had a Panasonic bath exhaust fan in my rack closet at home for over 15 years and replaced it for the first time about 2 years ago.  It's on a thermostat so turns on & off during the winter and stays on almost 24x7 in the summer.

The door is undercut by about an inch to allow air to be drawn in from the bottom and the fan is exhausted out through the roof.

Closet is about 2ft x 4ft x 8ft and has a full height rack that's had various gear in it over the years.

We use a fans like this all the time with good success. One of the keys you mention is the inlet of air down low. Proper air flow is important.

I had our designer add a fan to our drawings, and told her to add a "fart fan". She took me literally and add fart fan to our drawings. After a few chuckles it was changed to exhaust fan.

Yes, CFM is CFM and noise is noise. There are two types of noise -- noise conducted through the house structure and noise transmitted through the ducting. If you are venting outside or into the attic, duct noise is probably not an issue.

In terms of CFM, a fan will operate into a certain pressure head (some spec sheets will quote this). This is what the clothes dryer duct length and number of bends spec is all about. Length and bends create back pressure. One can create a situation where there is turbulence around the fan impeller, but no net flow out the duct. It's similar to wire resistance preventing enough current flow, given the available voltage.

Well, yeah, that's true. But for a given CFM, a lower heat load means the closet will be a lower amount of degrees warmer than the room. As your heat load goes up, the result of X CFM will be less and less.

I like the large lower air gap, too.


The first paragraph, now with some added details, also is added to by this. Whatever you tie into will change the CFM. If you try to exhaust into the wind at your exterior vent location, CFM will lower. All the factors are tied together.

If you had stated just that you might have gotten more help.


CFM is A key, and back pressure from the tubing, and heat load, are other keys.


The best thing you can do to help with that is to put a thermostat in the closet. When you turn on the system, the fan won't come on right away. By the time heat turns on the fan, the movie will be playing, so fan noise will be masked. When you're done and the fan stays on for a while, you'll be done -- and therefore not paying much attention to fan noise. And it'll shut off when things cool.


I haven't heard any ideas of how to relate the heat load to CFM or even to temperature rise assuming zero CFM. There's still a lot of facts to gather.

But chances are a quiet fan with minimal ducting and a control thermostat is all you need and will save you from learning all the formulas needed to tell you that what you put in was exactly right.

Try something and take notes.

In my opinion the thermostat should be mounted on or near the equipment.

Here is a quickie formula for airflow.

I use a Panasonic for my personal gear as well. Mine has been running 24x7 for the past 5 years. I don't notice the sound at all. One thing to note in newer high efficiency homes is that any air you vent outside the house has to be replaced with an intake fan due to better sealing. Otherwise you have an air deficit that can stress other air handlers.

[Link: amazon.com]

I am looking at a Panasonic that has 3 speed options. 50, 80, and 110 CFM. I may just pull the ducting off of the fan in the laundry room right behind the closet that never ever ever gets turned on. I will, of course, seal off the outlet in that fan. I can "Y" into the duct as well if I have the motivation. It will be a while before I feel like getting in the attic anyway so I have time to think it over..... It should cool down enough by Halloween. 😂

I will get a thermometer in the rack and monitor temps at each speed setting and see which works the best with the lowest noise. Thanks for the input.

Never vent conditioned air into the attic. Fart fans should only be installed in bathrooms and laundry rooms. If you must use a 110v fart fan then vent to a near hallway. For how much this fan will run you do not want to vent into attic.

If I'm wiring a new construction house I always do a 8x4 register in the rack closet & have the AC guy tie it into his return via 5" or 6" duct. That way when the AC is on its pulling all that hot air into the supply. I also install the cool components closet fan (fits perfect in the 8x4 register). That way it moves air whenever it gets to a certain temp.

Depends on the install but I usually do a fan in the wall pulling air from a hall way. All of this on a temp controller.

Cool components also makes a larger unit with its own filter as well but I have never used it.

I agree with Brett, accept if the house is spray foam, then attic blowing is fine. You're simply blowing into the same space.

So if I tie into the HVAC return, it will obviously draw the hot air out of the closet when the HVAC system is running (heat or AC), replacing it with fresh air from outside the closet through either a passive vent, or the air gap beneath the door.

When the HVAC system is NOT running, however, are you saying your additional fan is installed in the same air return duct, and pushes hot air out of the closet, and into the air return ducting as well? I am a bit confused on where that air will go when the HVAC fan is not circulating air through the close looped return/supply system. Will it end up being displaced back into the home through the HVAC supply ductwork? I understand the pressures will be very low compared to running the HVAC, but that is what it seems like would be happening in that scenario.

I am not sure why I "should not" vent into the attic (or to outside). My attic is vented to outside already. So I am not pressurizing the space at all. I understand that I would be dumping conditioned air into the attic/outside, possibly decreasing the overall efficiency of the HVAC system by a small margin. But this is the same thing that is happening when you run your bathroom fans, although on a temporary basis. Dryer vents are the same thing as well. Dumping hot air outside. The difference being that bathroom fans and dryer vents are not running 24/7, whereas my closet fan will likely run 24/7, at least in the summer months, even if on a thermostat set at 90-95F.

Active thermal suggests all of the above mentioned methods of exhausting air in their instructions. They mention exhausting into attic/crawlspaces, outdoors, HVAC return ducting, adjacent rooms, etc.

I could easily push the air from the closet into the laundry room. I could easily vent it to outside. I could easily vent it into the attic. I could fairly easily tie into the HVAC return. It would just require some kind of "T" splitter.

I will keep looking at options. But for this case, easy and cheap and fairly temporary is the goal....I will not be in this house for more than a couple of years anyhow. :)

Audiophiliac,

Depending on how much heat you must dump, you may not need any external air. Simply "stirring" the air inside of the closet might be enough.

In some cases I'll install a return air grill in the wall and use this for my exit air back into the room. Clients can often accept this as part of the house mechanics -- decorators are usually the biggest problem because they would like to replace anything that has a hint of science with a plant or a picture. Their goal is to defeat science.