Make-Up Air from Attic?

13 years ago

Had a phone conversation with our builder's HVAC guy this past week. We're just getting started (lot graded off last week). Wanted to ask about make-up air, given plans for a custom wood range hood and quality liner. I'm looking at a 1200 CFM inline blower (10 inch) in the attic with a silencer, such as Fantech, and a variable speed switch/rheostat. No decision yet on liner brand (see below).

Don't anticipate using the blower full blast much if at all, but our house is being built with the ARXX ICF blocks and it will be tight as a drum. When I asked about make up air, the HVAC guy said that all we'd need to do is pull it from the attic above the kitchen (it's a 3100SF 4BR house with only two bedrooms and one bath on the second story). We live in Florida, so just cracking a window is less than optimal for much of the year.

Even though there's a ceiling between the attic and the kitchen, that seems to be something of a zero-sum game, trying to replace air being exhausted from the house with air that's also in the house (if not in the kitchen).

When I asked him about hood liners, he said he usually only worked with JennAir (downdraft) and Thermador (which appears to come with mesh filters instead of baffles).

Getting our kitchen, bathroom and general HVAC plans right is really important to us. I'm not getting the sense that this gentleman is really on top of the kitchen part.

Comments from those with the experience to have an opinion?

Featured Answer

transitional

13 years ago

My husband has done HVAC for 12 years in Bradenton/Sarasota, Florida and also wouldn't recommend pulling in hot attic air. With a tightly sealed house there should be a fresh air make-up. This would allow fresh air into the house, generally hooked up to the return side of the AC system. Layman's terms: a pipe/vent that pulls air from outside straight into the AC system.

We ended up getting an Arietta Range Hood with only 400 CFM Blower. After we got home with our clearanced hood, I went straight to gardenweb to see if we got a good deal. Then I got scared that we didn't get one with more CFMs. Since then, we have cooked wright brand bacon (according to my DH the thickest, best-est cut of bacon in the whole world - read lots of grease) and it worked just fine. So 1200 CFM seems a bit much but we're not that familiar with the one you mentioned. I guess it would be nice to have the power if you ever needed it.

Hope this helps.

Here is a link that might be useful: Arietta Range Hood

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Comments (9)

davidro1
13 years ago
ask him about an air curtain.
hpxmirage
Original Author
13 years ago
David, thanks for the suggestion.

Quick question, though: in looking up "air curtain" online, they appear to be long rectangular fan boxes positioned over doors such as those you'd find at a loading dock.

If you have any more information about a residential appliation (such as where one would go), I'd welcome it.

Thanks again.
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davidro1
13 years ago
ok, I'll be less cryptic. 1st, I'm no expert. 2nd, I do know that an equal amount of air has to come inside as goes out the vent hole. 3rd, it seems you are in a climate that makes you want not to lose the conditioned air (which is understandable to me). 4th, I would arrange for an equal amount of unconditioned air to be pumped inside and sent to a grid rimming around the cooktop or range, and let that air be "the chosen" air to be pumped out of the house. This is because I always feel comfortable building my own apparatus to achieve my goal. If you are the same, and you make your own air curtain, in so doing you isolate the rest of the kitchen from the fine grease particulate matter that spreads everywhere whenever a bit of grilled salmon smoke rises up and escapes the hood canopy capture area. An air curtain curtails air movement. It directs the rising steam and grease particles to continue rising in a straight line to the canopy. You create a stream. You pull air in and you pull air out. One motor (blower) for each. The unconditioned air makes a funnel around the cooking surface and channels rising air to follow it to the hood canopy area and get pulled out of the house. Without this channel, the air that gets pulled out of the house can come from any direction and that lets rising steam and grease rise up and slip away in the opposite direction. Very disorganized.

HTH
hpxmirage
Original Author
13 years ago
OK, got that, thanks!

I'm afraid my mechanical skills extend only to boats, cars, motorcycles and 1911 pistols.

I'd be better off trying to build a space shuttle than an air curtain. Both would probably crash and burn. :-) Thanks again, though.

Any other ideas re: make-up air for residential use?
jdew1920
13 years ago
Davidro1 is right that when you expel air, an equal amount of air will replace it. A older house is not nearly air tight so there are locatons where air will be pulled in - around windows, doors, switchplaces, recessed lights, basements, crawl spaces, etc. A newer house or one that has been sealed up, can be so tight that not enough air can get in, so you can't exhaust as much air as you should and possibly you will pull from locations you don't want - like through bath vents or even a furnace or waterheater chimney - that can cause CO poisoning.

Your attic is not considered part of the conidtioned space and its presumably vented, so in a sense it is the "outdoors"- so your HVAC guys idea of pulling air from the attic in theory is OK, but I doubt it meets code. Plus if you have anything vented into the attic like a bath vent (which you shouldn't but a lot of them are), then you can just be recirculating house air. Plus, I would imagine in florida the attic temp is usually very high, seems like you'd be better off pulling air from outside.

There are passive make up air systems that simply allow air to enter the house when pressure in the home exceeds that of the outdoors (a simple damper system). Something like this may provide enough additional make up air so that you avoid other issues.

equaliz-air dot com
John Liu
13 years ago
Hpx, are you a pistolsmith by any chance? I was curious.
cooksnsews
13 years ago
Transitional's hubby does it the same way it is done where I live. Except I don't have a/c. My MUA is drawn into my furnace system, and when the temperatures dictate, through a pre-heater. That's code here...
hpxmirage
Original Author
13 years ago
Thank you each for your comments. Since this house will be really tightly sealed, MUA will be essential, and I very much appreciate transitional's comments from her husband. Pulling scorching hot attic air into the main body of the house I'm paying a lot to cool with A/C does seem rather counter-intuitive, doesn't it?

Johnliu, "inveterate tinkerer" is a more accurate description than "pistolsmith." I have two good friends who are the latter, and while i have taken a one week build-your-own course from one of them, I'm now about passably qualified to clean his files.

transitional and johnliu, you both have short emails.

Make-Up Air from Attic?

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