Make up air set to a certain CFM?
Scott
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kaseki
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Braun make up air damper--newer product, know anything about it?
Comments (40)"All that said, if I had an HE furnace within the habitable space in our house, I would definitely make sure it got its combustion air directly from outside the envelope. Apart from anything else, I would not want to draw unconditioned air into the house to provide combustion air for the furnace". Couple of points/questions still on this topic, as I draw closer to actual demo date. First, our local community permit office is now pushing enforcement of mua damper such as above (where as before, they knew, but weren't enforcing). Broan8T or other universal 8" mua damper: for better or worse, my plan is exterior unconditioned air, with critter cage and down line filter; the exterior duct will be 10' away from exterior vent pipes, chimney, and at 1' above grade. How to ensure the newly made 8" exterior hole through our brick is not a magnet for wetness/other (foam insulation) Is a big concern for me. The 8" duct will run a straight line of about 15' through an open crawl space (but not draw from it), then turn to run in the small furnace room to the return of the 80% efficient furnace. Not wild about this solution but it's feasible and reasonably priced (except for me picking up it's installation/brick cut/return duct cutting/ mua analysis, low voltage interface with hood etc). Low voltage unit in hood will communicate with basement duct/furnace to kick on when hood does. Regarding our house envelope: I've worked hard to update chimney rain caps/proper pointing and installed a new, properly size chimney liner, as well as new properly sized ducts for both our gas furnace/gas water heater. I also installed for the first time four window well covers which surround exterior crawl space vents. These slightly angled well covers are on raised clips which allow air flow in for mua. I'm watching this situation closely for sufficient mua, as prior to this the exterior crawl space vents were usually open for free access to unconditioned exterior mua. I'd say the laws pertaining to mandatory make up air (for largely =/ >400 cfm vent blowers) are ahead of reality for many GCs and homeowners and should be given more time and known code meeting types of mua. I understand the need for mua to avoid backdrafting and carbon monoxide poisoning. The industry is just not there yet with feasible solutions. It's the make up air engineers and specialists who benefit the most, as they get hired to check your leaky envelope and help with the universal damper installation plan, if they even agree to come to your house. This is an important and big investment for most homeowners. Do due diligence and bring your check book. Plan early, no your code and invest yourself. Good luck. edited for spelling etc. This post was edited by SparklingWater on Wed, Apr 3, 13 at 16:11...See MoreNew construction: venting and make-up air for 48'' range
Comments (4)Wow! A rare case where the aesthetics part of the performance-aesthetics-economy: pick-any-two limitation is not a factor in hood selection. But first, given a sealed household, I would strongly recommend obtaining a furnace kit to use outside air. This will avoid the possibility of the MUA system not working perfectly and the hood causing negative house pressure and hence backdrafting of the combustion appliance. I know that such devices exist for Beckett burners, and would guess that there are adapters for other burners. As the OP correctly notes, a 200 cfm ERV is not going to cope with a 1200 cfm vent hood. (Actually, what would happen with a sealed house is that at full power, the hood would pull the cfm the ERV would let through into the now minus a couple of inches w.c. house pressure.) So MUA is essential, and in the mid-Atlantic region would be pretty uncomfortable in winter if unheated. Depending on one's tolerance for heat and humidity, cooling in summer might be optional or not. We are starting to get into the realm where performance-economy, pick any two is applicable. MUA can be roughly characterized as passive or active. By passive is meant no fan in the circuit. Active uses a booster fan to keep the house pressure stable. No-fan only works for simple ducting with a vent hood air flow controlled damper. (A recent post here provided some sources for these.) If a filter is used at 1200 cfm (or whatever flow actually could be pulled with all the doors and windows open, then the house pressure will drop. One can see on websites selling filter packs that the pressure drop at such flow rates is too large for combustion appliance safety, which require negative pressures not be greater than 0.03 to 0.06 inches depending on appliance type. Active is needed to overcome the filter restriction. It may be needed to overcome heating heat exchanger restriction and/or air conditioning heat exchanger (expander) restriction. The difficulty with active is balancing the MUA air flow rate against the variable hood flow rate such that the house pressure is near zero. This usually requires a control system of some sort, and can be a "project." What to do? What to do? Only one free-of-processing-controllers active MUA has occurred to me. In the simplest embodiment, the hood control is connected to two parallel wired identical fans, one in the hood exhaust path and one in the MUA path. Then the two will (try to) operate at nearly the same flow rate at every control setting, and one only needs to adjust the MUA duct restriction until it matches that of the hood path. More exactly, adjust the MUA path so that house pressure falls very little as the hood is turned on. Note that this doesn't account for bathroom fans, fireplaces, or other exhaust flows not due to the hood. In such cases, PID control of the MUA fan would be needed. In my case, due to a 1500 cfm hood, 1000 cfm over-oven vent, fireplace, and three bathroom fan household, I am building an active MUA that will use an axial blower in the 2000 cfm regime. It has to overcome the pressure loss of its intake vent, its filter, and its heat exchanger (which is hot water pumped from my oil burner). Control is via a Fuji PID controller operating from a BAPF differential pressure sensor. The motor power control is not yet selected, and a lot of sheet metal action is still needed, along with further attic revisions that I seem to have trouble getting to at the needed rate. I recommend the OP and/or his HVAC person read the "Kitchen Ventilation Systems Application & Design Guide" that may be found at Greenheck's web site. It periodically moves around, URL-wise, so a Google search by name may be fastest. Greenheck or one of its competitors may be able to provide what you need for considerably less agony than a do-it-yourself HVAC project would. kas...See Morevery interesting articles on CFM and makeup air; 250 cfm suffices
Comments (11)Regarding clearing smoke from burning, a nontechnical input. We bought a very low-end insert special order from Lowe's. Don't know the CFM, but there was none lower available as this was the least expensive unit we could find. Soon after moving in, I was called outside for a minor emergency that made me forget all about what was on the stove. Hiking back afterward, though, I remembered fast when I smelled the black smoke of badly burned food. We're not talking scorch here. Scared for our house itself, I ran up the hill, the smoke with me all the way, burst through the kitchen door--and left the smoke completely behind. Outside. Although any flames had burnt themselves out, the pan was still charring away on the stove, but our little-engine-that-could vent was quite adequate to its task. There wasn't even anything to clean up on the backsplash behind the stove. I actually hated to move the pot away from it long enough to rush it outside. I don't regret that very satisfying demonstration of our vent's capability, even if I did have to throw a badly warped skillet away. The end. :)...See MoreAir Make up for high CFM kitchen Exhaust
Comments (13)Thanks for the comment. It's a 10" duct and the blower is inline remote with a muffler. It's all on the exterior of the house past 10" thick ICF walls. The blower itself will be suspended by porch rafters to reduce vibration transmission and the porch rafters are tied to the house with a ledger board on the exterior of the ICF so there's little to no vibration transmission into the house. The inspector is requiring a 10" MUA duct. I know that at full blast, it's not going to be whisper quiet, and I'm only expecting to use it full blast in rare occasions, but we do want the option for that many CFMs. As I mentioned above, the range top is 48" with four burners, a char-broiler, and a griddle for a total output of 111000 btu. I doubt we'll ever use everything full blast at one time but my biggest concern is smoke from the char-broiler and grease/oils from the Chinese cooking I frequently do. The MUA will come through the toe kick of the range top base cabinet so it helps create an air curtain to pull out smoke/grease/oil. Believe me, I have the same concerns about cold/hot air in the MUA, but to achieve the worst case scenario for cooking containment, we need to look at corresponding CFMs. I'll have to see how the controls open the MUA damper. I wonder if it's the case where the damper only opens over 500 CFMs, but I would imagine that with our tight house construction, we might not want that....See Morekaseki
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