Filter barometric relief / gravity damper for makeup air?
I’m currently looking into parsimonious makeup air solutions for a ~ 600 CFM remote-blower island range hood. As an air pollution scientist, I really want to get the hood system right, and this seems to mean >400 CFM for my hood. I also am trying to produce a simple and lower-cost system to bring in the makeup air because I — stupidly — forgot to budget this into the project. My contractor favors a barometric damper, which is fine for me for a number of reasons (especially as it might produce makeup air for a number of other processes in the house), but I’m not stoked about bringing unfiltered air into the home. Better than the alternative (down the chimney or in through crawlspace/attic), but not ideal. An active fan system like Joe Lstiburek suggests in his Manure article could be made to have an in-line filter, but I believe this system is quite a bit more expensive and would remove any knock-on benefits of providing makeup air for things like bathroom fans and the dryer. I also don’t like the idea of dumping MUA into the return plenum, re-entraining dust and all sorts of crap that gets stuck in the return ducting (since there’s no filter on the return grills in my system).
I imagine placing a substantial filter over a barometric relief damper would cause too much static pressure (I think code requires a 2-pa sensitive damper), but perhaps there is a product someone might know of that includes some level of filtering — even if just a pollen or tiny-bug filter?
Thanks!
Edit: we do have a Broan 160 CFM auto-balancing HRV pulling exhaust at ~ 1/4 of total from the kitchen. Any chance I can somehow make the 400-600CFM of makeup air run through the HRV without damaging it (seems highly unlikely, especially if auto-balanced) or through the HRV supply ducting to take advantage of a filter downstream of the HRV?
Manure article: https://buildingscience.com/documents/insights/bsi-070-first-deal-with-the-manure
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Personally, I feel make up air is highly overrated. Even "tight" modern houses aren't really that tight, it's not like an exhaust fan is going to suck the water out of your toilets or make your ears pop or even be noticeable.
If you're not using any combustion appliances you don't need make-up air and I would recommend against it even with a 600 CM vent. Certainly the other fans in the house don't need makeup air. If you want makeup air for the stove vent just wire up an electric damper in parallel with the fan and be done with it.
Look into the RangeRelief system. It is a damper wired to a sort of manometer that you install in the duct of the range exhaust, which causes the damper to open when the range is exhausting.
https://www.aircycler.com/pages/rangerelief
Their site shows it connected to the HVAC system, but mine is not - it is just a Panasonic EZ Soffit vent, connected to 4" hard duct, with an inline motorized damper, more 4" hard duct to a boot and what was a return grill.
I replaced the return grille with a 2" filter grille and use a 2" MERV 8 filter. It is unbelievable to me how dirty that filter gets. Very happy that I'm filtering that air.
Thanks for sharing! Any chance you have a picture of your grill setup that you’d be willing to share?
It's just this product, installed on the ceiling against a duct boot. Obviously the photo they show with this is for a square one, and the size linked is rectangular...
https://www.plumbersstock.com/shoemaker-fg2-10x6-10inx6-filter-grille-2-filter-stamped-face.html
Nice! Thank you! I'll take a look.
I wonder if you considered the pressure drop produced by the filter affects the CFM coming through the RangeRelief system in any way that is meaningful under code? Code seems to require makeup air rated to provide CFM approximately equal to the range's exhaust rate (and be sensitive enough to begin operating under a <= 0.01 in/w/c [3Pa] differential in the system)
finePNW,
"I’m not stoked about bringing unfiltered air into the home"
I think whether that matters is very dependent on where you are bringing in the make-up air. If it is in close proximity to the range-hood, and most of the new air is being exhausted, filtration would seem to less useful than if it was across the room.
That’s a good point. I should check out some Schlieren imagery to understand where/how/under what context I might be able to get most of the makeup air back into the hood.
finePNW,
You may find comments #7 and #15 under this article useful:
https://www.greenbuildingadvisor.com/article/makeup-air-for-kitchen-exhaust
Very helpful, indeed. Thanks!
Hood performance has little to do with CFM and a lot to do with hood shape. You want something with a wide opening and large capture volume. Generally most of the sleek designer island hoods don't work all that well despite the big CFM numbers. Most also don't deliver nowhere near their nameplate CFM with a typical install.
I would go for a quiet 400 CFM (actual flow including hood, ducting and wall cap) blower, pair it with a well designed hood and skip the MUA.
If you are going for an MUA, I would pick one of the passive kits that includes a motorized damper, current sensing relay for the range hood and an in-line filter. Unlike a gravity damper, most of these come with a damper with a gasketed blade so when closed it is well sealed. These parts are also readily available if you want to mix and match and DIY your own setup.
As always, very good points. Thanks!
HVI seems to recommend 450 CFM for my 36" island range, but I also understand induction ranges may be able to get by with fewer CFM. Might be worth the gamble of 400 CFM, but air quality is priority #1, so I'll have to do a bit more thinking/research on it.
Also a bit late to this conversation -
Has anyone successfully put together an Automatic Make-Up Air Damper that works of a differential pressure switch rather than a pressure probe in your hood exhaust vent?
I am looking for what type of barometric pressure switch people have used. thank you!
I haven't built one of these systems myself, but I've drawn up a few designs for others. You need a differential airflow "proving switch", and you need one that is pretty sensitive like this:
https://www.supplyhouse.com/Cleveland-Controls-AFS-222-112-SPDT-Adjustable-Differential-Air-Pressure-Switch-05-12-0-W-C
You can use that to trigger a vent to open using a moter operator. You need to be careful to set things up so that you avoid oscillations, such as when the damper opens the pressure change goes away so the switch causes the damper to close, which brings back the pressure difference so the switch causes the damper to open, which makes the pressure change go away so that the switch causes the damper to close, which brings back.... You get the idea. The easiest way to do that is to use the pressure differential across the exhaust fan itself to trigger the damper, since that air path isn't directly affected nearly as much by the operation of the damper compared to the difference you'd see just between indoor and outdoor relative air pressures.
The other way to do this, if you really want to sense the difference between indoors and outdoors is to use a time delay relay so that operation of the pressure switch triggers the damper to open and the time delay relay then holds that damper open for some set period of time (15 minutes, etc.). This doesn't solve the oscillation problem, but it greatly slows it down and should avoid any problems with longevity of the equipment involved.
My preference is typically to just wire things so that the damper opens whenever the range hood fan is in operation, and skip using a pressure switch entirely. You can do this with current sensing relays set to detect the current drawn by the blower motor, those current sensing relays then operate the motor actuator on the intake damper. You can do this all with 24v control wiring using standard HVAC components, and the low voltage 24v system lets you wire it with thermostat wire and not "power" cabling.
Bill