Last in first out: My Wolf/Broan external roof-hugging blower (which aims down the roof line) seems to avoid being gagged here in NH USA even with one-foot wet snows. However, I can easily see that there could be conditions (Buffalo NY) where the snow depth would preclude its use without taking additional steps. In any case, I would suggest a different approach. An upblast unit (on the smallish side, not a massive restaurant unit) mounted on a base suitable for the snow depth you would have to deal with, should stay free of obstruction. Upblast units are more obvious than down slope centrifugal units, but most will not notice or will blank out the new feature after a few views.

Note that whether the fan is internal to the hood and pushes out through a roof cap, or is embedded in a larger roof cap, one has the same problem with snow. Go external, you will not regret it unless your roof is difficult to access. In that case, an internal fan may provide easier repair, if ever needed, and also more noise. You will still need a roof mount that brings the cap up beyond the possible snow line.

MUA: You have is the most difficult problem in residential MUA, balancing house pressure, filtering and heating, dealing with fireplaces and combustion appliances, keeping toes warm in the kitchen. The complex of competing demands calls for a complex answer, which is not the direction most will want to go, so lets see if some simplification is possible.

First, the amount of time needed for higher flow rates needs to be considered. If hours, then like for restaurants heating is needed to bring the air to tolerable temperatures. If only for the duration of grilling or wokking, then some cooling may be allowable. One has to consider that there will be mixing of MUA and kitchen air no matter how the flow path is configured.

Even if the house is relatively unsealed (perhaps especially if the house is unsealed), air leakage allowing reduced MUA system flow rate will cool the whole place off. At -40F/C this won't take long at 1000 cfm.

How to heat the air? One approach is a heat exchanger in the path (like a car radiator) heated by a water loop taken from an oil-fired hydronic heating system. Another, significantly less hassle system, would use electric heating coils. This electric heating may be expensive, but it is only for short durations during limited seasons, so may be economically tolerable.

MUA can be introduced anywhere that it can get to the hood without causing significant cross drafts. If released under the stove, then it will cool off the cook. It may be possible to release it so it rises up behind the stove. One needs to confirm that this doesn't violate some requirement in the users manual for the particular stove. The goal is to replace the air rising from the pans and not displace the air rising from the pans.

I recommend you review this whole subject using some of the references called out in My Clippings. In particular, the Greenheck brochure on ventilation available somewhere on their website can provide a lot of basic concept about the subject.

Consider the ducting requirements and possible paths, both coming in and going out. If possible, and only if using an in-line or roof-mounted blower, use a silencer to further reduce the noise. I can attest that it is a pleasure to cook and have the sizzle noise dominate the blower noise.

Without addressing it adequately, an MUA path with restriction will lead to lower internal house pressures, and it doesn't take much to backdraft. In such cases an MUA blower is needed. You may be ok with one that just runs at a single speed when the hood is on, or when the hood flow rate (measured with a vane in the hood duct) is above some threshold value. This won't balance the air pressure, but will suppress back drafts.

The large building technique of constant MUA flow rate with a damper controlled bypass is another possible scheme. You might imagine a blower MUA system dumping into a basement with a register under the back of the stove, with another pressure damper allowing the excess pressure back into the intake side of the MUA blower, or even releasing air back outside. Unlike the mechanical space allocated in a large building, a house has a lot already packed into it so every situation has a potentially different solution.

I probably didn't touch on every question, and introduced more of them, so feel free to quiz us further as necessary.

kas

Wow kaseki!! Thank you so much for such a detailed and thorough response. With all these requirements it appears that I'll have a very expensive range indeed.

I originally budgeted ~$10,000 for the range with hood, but if you include external blower, and MUA unit it's actually closer to $15,000 without even touching energy cost. That is more than my winter vehicle is worth! Is that a normal amount for someone who installs a 36" pro style range?

I've been thinking about going induction after learning about all the assocciated costs involved... but I asked a few guys at work what they thought - "You don't work your bag off up here to NOT get what you want. Get what you want" (I work 300miles north of my primary residence and commute between my income property and primary residence week in, week out.)

The approach cooksnsews took shown in the image at the link was reportedly fairly expensive, but I think some lower complexity might be possible for those on a budget. Prices in different locales may be different also.

I consider kitchen reno's to be money pits of indeterminate depth, so I can't comment on normal.

kas

Here is a link that might be useful: topic called myths about cfm's and mua

This post was edited by kaseki on Thu, Dec 11, 14 at 11:17

Based on the location where I live I think a heated MUA would be the only option that makes sense. A passive 12" hole in the wall to the basement would turn the house into a freezer in no time! I was looking at a 10-15kW unit from Electro Industries (I'll have to confirm sizing with my GC/HVAC contractor) They are all in one units and I read that they are around $2000 for the 10kW model. That doesn't seem too expensive IMHO.

Here is a link that might be useful: Make up unit here

It appears that industry is starting to catch up with the residential code promulgators, MUA-wise.

kas

You can run the Make Up Air via the air recirculation fan, which in turn blows air around the whole house when your hood is turned on. if your thermostat drops by 2 degrees the heating will kick in.

I would suspect this has to less expensive than other options.

It depends, Trevor, on the rate that the house furnace can add heat to new (-40F?) air. Most house heating systems are scaled to a particular rate of heat loss through the walls, plus some extra so rooms can heat quickly when desired and hot water can be made (where applicable). The "advantage" of a really "tight" house is that the furnace can be smaller. Open the windows and turn on the hood and see whether the house can stay warm.

Heating a 1000 cfm of really cold air to near room temperature has a simply calculable BTU/hr rate (get values from the web), that may be higher than the furnace capacity. More than100k BTU/hr heating rate may be needed for some cases.

Even systems not legally needing deliberate MUA that depend on house leakage may cool the house faster than the heating system can compensate.

kas

We weren't required to install a MUA system in our now very tight house; I just open a nearby window when I turn the hood on. It's inexpensive to implement and works perfectly, except for what can be a pretty cold draft from the window to the hood. That affects only a very small area of the house, only for the short times the hood is on high. The idea of paying a fortune to heat the air you are about to exhaust to the great outdoors seems dumb beyond imaging.

At low fan settings the ERV and general leakage seem to provide sufficient air, I only need to open the window when I'm actively cooking and need to crank the hood up.

We installed all sealed combustion appliances, so backdrafting is not a concern.

If I were a lot wealthier I would have considered ducting outside air in to a point under the range (aiming for a sort of laminar flow situation), with a powered damper coupled to the hood blower. There's no way I would ever waste the energy on tempering the makeup air in such a system.

Contact some commercial HVAC contractors in your area and pick their brain about how they handle MUA for restaurants in your area.

It seems you would be a good candidate for a MUA system where the MUA comes in around the perimeter of range hood and then is sucked back out with the smoke from cooking. This seems far better than haveing the MUA come into some other area of the house and cool it off (making it uncomfortable) or having a huge MUA heating system that can keep up with a 1000CFM blower.

A perimeter MUA system around the hood would require more design expertise and expense at the hood to design a system that works correctly, but it would cost a lot less to operate. Perhaps even a hood-perimeter MUA system would need some heating to keep the cook comfortable, but less heating than a different MUA system that would potentially have to "make up" for heated air pulled from throughout your house.

See the face supply and air curtain commercial hoods below.
http://www.accurex-systems.com/Products.aspx?m=s&s=1

Billy

For more information see this article.
Billy

Here is a link that might be useful: Designs for Makeup Air

The critical aspect of air curtains and hood feeds of MUA is that the air that has to be replaced is that rising from the pan, starting down at the pan, and replacing it elsewhere can disrupt the capture of the rising effluent from the pans.

My expectation is that air curtain type MUA can work when the hood aperture area is much greater than the effluent cone area at the hood. MUA from somewhere still has to reach the stove top.

In commercial applications, the kitchens are generally quite warm, and a cool breeze onto the cook from above might be welcomed. This is not necessarily true of a residence in Alberta, or even in New Hampshire.

kas

kaseki,

I agree with everything you say. The PDF article I linked to shows the effectiveness of various approaches.

Talking with a local professional will be helpful for OP.

Maybe MUA under the range would be a good solution, especially if it could be partially tempered as to not be too uncomfortable. I can't see any reason to have MUA delivered far away from the hood.

Billy

hvtech42,

A damper might be fine but what you're missing is that WHERE the makeup air enters the house does matter. That's what we're discussing near the end of the thread.

It matters in terms of how much heat you lose and whether or how much heated air you might need. My last suggestion was to have it enter near the bottom of the range.

BTW in my house we open an awning window over the kitchen sink for makeup air for a 1400CFM hood. All of our appliances are direct vent so there are no backdraft issues. Yes, my wife complains sometimes in the winter but it's not too bad -- temp in the 30s. I suspect at minus 40 degrees in central Alberta it's a different story.

Billy

This is what makes MUA such "fun." If the air is conditioned, it can be introduced distant from the kitchen or at least distant from the hood and have the best chance of not disrupting the rising effluent plume. If the air is unconditioned and cold, then close proximity is called for (although it is unlikely to be so close as to not chill-out the cook. This could have long-term ramifications. :)

Insertion under the range is a good approximation of proximate, but might have these deficiencies:

o Some ranges may not like this. Someone on this forum in the last year, I think, pointed out that high-end Brand X gas range instructions prohibited it. I don't recall who X was. I do not know what the basis of the manufacturer's objection was.

o For cooktops, cabinets will be in the way. A grill at the feet may be used instead of a cabinet base, and for peninsulas and islands, another on the other side is plausible. Keep in mind that the grill will have to have a rather strong air velocity unless the grill is as large as the hood.

Alternatively from floor insertion, a slotted counter top design around the cooktop would provide an ideal air feed location, but inadequate area for the flow rate. Also, it could be an opportunity for difficult cleaning.

Pop-up vent systems run backwards come to mind. The air flow onto the cooktop could be disruptive to the flame pattern, so probably should be aimed outward. Flow would likely be too low without a very large pop-up.

kas

In Bluestars installation manual it states "Any opening in the wall behind the range and in the floor under the range should be sealed." I will have to contact them regarding this statement, but it appears that it's not supposed to have MUA supplied under or around the range.

I was considering ducting the MUA behind the fridge to flow over the condenser coils. This would likely reduce the energy needed to condition incoming air.

@hvtech42: One of the reasons I wanted this range was so I could grill indoors when it gets cold. I am the only cook in the house and I would not be concerned with a draft. What I WOULD be concerned about is venting very very cold air directly into the kitchen; causing problems with condensation where ever the ice cold MUA enters the kitchen.

@rwiegand: In perfect truth the lows at night are -30F or colder for a large portion of the winter. If I had a window open the window would freeze open. This has happened to me countless times as a youth and my father had to replace the window opening mechanisms due to stripped gears when I tried to close the windows.

Well this is anomalous; I got this email yesterday from Houzz, but there seems to be no new comment here in the thread itself.

I look forward to learning the rest of the message from @Franco Oyuela or to the eventual appearance of the message in this thread.

I wonder if the poster deleted it after Houzz sent the notice to you.

That plus not noticing that the thread had surfaced anyway.

It was SPAM.

Thanks, LWO. In such cases, it might be nice of the admins removing the message to replace it with a couple of words.