You won't regret getting a bigger/more powerful hood if you have the space for it, and proper makeup air.

Yes, I have the space for a bigger hood.

Speaking of make up air, the sales person suggested an inexpensive approach -- install a 10" BEST universal automatic air damper somewhere inside the house, rather than tie the make up air system to the HVAC system.

Does the air damper approach make sense? I am in NJ.

I am replacing the air handler as part of the kitchen remodel, so maybe it makes sense to tie the make up air system to the HVAC system... I am not exactly sure what's involved in doing that. Say if replacing the air handler costs $5K total. Approximately how much more would it be to add a proper make up air system?

Thank you very much.

Edit to add:

I just read a bit more on the forum about makeup air system. It seems the passive approach (i.e. install an automatic air damper) is acceptable.

This post was edited by ILoveCookie on Tue, Mar 25, 14 at 15:34

One advantage of having a large vent is that you can run it on lower speeds a lot of the time which will be quieter. IE, a 1200cfm running at half speed will be quieter than a 600cfm at full speed.

The other thing you need to consider with the barometric damper is some kind of inline filter and heater. The HVAC guys should be able to bend some tin to make up a filter holder. Larger is better (less pressure drop). Thermostatic heaters are available in various duct sizes and BTUs for a few to several hundred dollars.

Replacing the blower is one thing. Adding ductwork is something else and would need to be discussed with the HVAC guys. Doing the outside stuff (cutting a hole for the intake) might be done by GC (carpentry).

I'd go for the larger vent too. I don't think it's overkill. I'm going to get a 36" BS RNB and I'm looking for a similar hood to what you're looking at, 1200 cfm, 27" deep (though I want a 42" wide). The point weedmeister made about running a more powerful hood at lower speeds is good. I had a salesperson make that same point to me. I'm still figuring out which hood to get. Ventahood's filter is pretty easy to clean I believe. The same salesperson showed me how easy it is to take off, and then you can wash it in your sink or put it in the dishwasher. One thing I didn't like about VAH is it only has two speeds. I like the idea of having multiple speed options depending on the type of cooking you're doing at the time. I haven't ruled out VAH yet, but hoods are really challenging to decide on imo. I've got all my other appliances figured out, but the hood is not easy. I'd love to know what you end up getting and why once you decide.

Been there, did that. :) I have a three element Induction and a two burner gas under one large hood and had the same dilemma. They stopped making the intermediate speed and 600 cfm, like my old hood, didn't seem like enough for all guns blazing. I got the 1200, with continuous speed control (which you can probably add if it doesn't come with it). I don't regret it at all. It's not quieter on low because the low is higher, but it's worth it. Low is good enough for small stuff: a little steam, a little saute, a simmer, Somewhere in the middle for a quick sear. High when every burner is blazing away! On low to medium I don't need make-up air. There's a sufficient volume of air in the house, and sufficient cracks for refilling it, that there's no problem. I'm in a temperate climate where it doesn't affect the HVAC. For higher speeds, I crack a window in the kitchen. At that point, there's enough heat coming from the stove that the fresh air moving through is quite pleasant. ;)

I would go with 1200cfm. People, including many sales staff tend to be fixated on the size of the stove or btu to dictate cfm. I have a 1200 cfm 54"x27" vah over my 48" bs, and when woking I couldn't imagine a lower cfm. Since you can wok as easily on your 30" as I can on my 48 I would highly recommend 1200.

As for the the claims by vah having an "equivalent" rating higher than actual cfm I think its a bunch of bolagna. And as for vah being quiet? No way. Ive had two, first one was either 300 or 600 cfm (cant recall) and current is 1200 and they are anything but quiet. If I was to buy a hood today I would look around at others. Not saying I wouldn't buy vah again, but I would take closer looks at competition.

Well, I'll disagree. I have a 600 CFM hood over a 30" DCS range and I rarely run it on high even when wokking. Depending on the code in your area, you may not need make-up air with a 600 CFM hood and for me that would be the deciding factor. My hood is only 30" wide and with flanking cabinets that is not a problem, but I do wish my hood was deeper - I do get some grease on the outside front of the hood.

A plug for 27" deep hood which quite frankly, isn't even deep enough. I was worried about standing underneath it and the hood being in the way: no problem at all.

I don't remember how many bazillions of cfms we got but it's a lot, with an inline blower placed high up in the attic. It's still noisy. The variable fan is way-nice; I would not, personally, install a system without it. I use the whole shebang dull to take-off roar.

I can't speak to the necessity of the monster suck. What bad thing happens if you don't have enough suck? I presume a smaller version of what happens when you have, say, no hood at all, which I lived with for the first 50 years of my life. It wasn't the end of the world, but like everyone says here, once you experience a good hood, you kinda never want to look back. It is really nice to live and work in a kitchen that's not coated with weird nasty sticky ick. I think that's the bad thing that happens when you don't suck enough, the surfaces suck instead.

If you can afford it, I'd go for the massive one with a variable speed dampener that will give you the best of all worlds, less noise at more moderate speeds, and the ability to wick it all away when needed. It is a purchase I have never once regretted, fwiw.

I have the 30" RNB with a crummy hood that goes 320-560 CFM. I think a 36" hood up to 600-800 CFM will be adequate for my needs, but I want one a lot quieter than what I have.

I've been having a really tough time finding a hood. I got some good advice here in my thread "super-quiet 600+ cfm range hood for condo - mission impossible??"

My top pick would so far be

Kobe CH9136SQB-1
QuietMode™ 300 CFM (1.0 sone)
Speed 1 370 CFM (1.4 sones)
Speed 2 440 CFM (2.8 sones)
Speed 3 540 CFM (3.5 sones)
Speed 4 640 CFM (4.2 sones)
Speed 5 760 CFM (4.5 sones)

22" deep (I would consider building out from wall to improve capture area)

suitable for 6" duct

underside is somewhat concave which should improve performance

I also have a very similar duct setup to yours so I'll be interested to know what you choose!

This post was edited by feisty68 on Wed, Mar 26, 14 at 1:55

I did a little geometry and it looks like I'd have to put a 27" deep hood super high due to my 6'2" husband to avoid head-bumping - high enough to undermine the suck factor of the hood. That leaves the dilemma of whether to have a shallower hood/lower CFM, or deeper hood/higher CFM (and more $$$). Also, the higher the hood the more noise.

I think the OP might be in the same situation as me where the external exhaust is too close to make a remote blower feasible.

Just to correct some miss-impressions by sales people: The air flow rate (CFM) required is proportional to the aperture area of the hood and to the uprising effluent velocity from the HOTTEST pan. It does not matter how many burners are on if the aperture is large enough and the required velocity in the aperture is met.

A VAH hood will not move its rated CFM unless the hood is standing alone in a field. There are pressure-loss restrictions from the ducting to the outside, and make-up air (MUA) pressure-loss restrictions, even from replacing air through a window screen.

However, giving VAH the benefit of the doubt that their reported CFM is for the hood with blower, then baffle pressure loss in conventional hoods, along with some internal transition losses, will make the ratio of real-world CFM to zero static pressure CFM for conventional blower hood duct and MUA systems a little lower than for a comparable VAH hood with duct and MUA systems.

For conventional systems I always assume a 2/3 factor unless analysis suggests otherwise, and analysis requires not only calculations of losses through all the pieces including the rarely specified hoods and baffles, but also the fan curve. Thus, barely educated guesses are likely to be the best one can have before installation and the opportunity for measurement occurs.

The second mis-impression I'd like to correct is that hoods suck effluent from the pans, or even from the area between pans and hood. Hoods do have an input air velocity, and this air comes from the area around the cooking zone, (albeit rapidly decreasing with distance) and this velocity helps pull effluent into the hood, but hot pans can emit effluent at 3 ft/s upward, and this velocity gets the effluent to the hood without much help from the hood doing any sucking. What the hood has to do is have enough air velocity that when the rising hot effluent hits the hood parts, the momentum change tending to reflect the effluent out of the hood (visible in Schlieren photos as a curling out) is overcome by the hood's own air velocity.

If, for some unimaginable reason, you wanted to remove odor from the kitchen emitted from a bunch of cilantro set on a cold cooktop, then all you would have to work with is the hood removing air from the kitchen, which is certainly suction at the aperture, and by extention there has to be some airflow to the hood at the cooktop, if not suction.

In any case, people bend over to get their heads under hoods, so a stick figure cartoon will help reveal what hood height is sufficient to avoid bumps. The higher the height the hood is placed at, the larger the hood aperture has to be to capture the rising and expanding effluent, and the larger the CFM capability has to be to meet the rule of the first paragraph.

kas

This post was edited by kaseki on Thu, Mar 27, 14 at 11:25

feisty68 you might want to have your husband go to a store and see what hood height he needs. My husband is 6'1" and this was my concern also with a 27" depth hood. The salesperson I referred to in my original post was 6'. I asked him about mounting hoods higher then the rec of 30" above the cooktop b/c of my husband's height. He demonstrated with himself that he didn't hit his head on a 27" b/c you do bend a bit when you cook. I do think I would want to mount it 32-33" higher than the cooktop to be safe, but my husband will be going in to "test" this issue, as I'd like to mount it as close to 30" as possible, though I think 30" will be a bit too low.

Thank you so much for your inputs!!

I am inclined to go with 1200 cfm, 27" depth (if Prizer / BlueStar makes it). The main goal of my kitchen remodel is to significantly improve the cooking power and ventilation. If I don't go with 1200cfm, I think I might regret down the road, which will defeat the purpose of this remodel. I am sure any hood will be better than what I currently have (downdraft)...I just don't want to regret my decision.

weedmeister -- I am going to need to look up what a barometric damper is, and try to educate myself before talking to an HVAC guy about inline filter, thermostatic heater, etc.

plllog -- I read on the forum that some people put their make up air thingy under their fridge, so the cold air could get heated by the fridge somewhat. Very clear. :)

Regarding the continuous speed control, I think Prizer / BlueStar hoods only come with a fixed speed control. ctycdm posted a while ago that they don't recommend using a variable speed control with their hood. I never used a continuous speed control before, so I guess I won't miss it?

Converting a 3 speed hood blower to continuous control

``I was informed by my hood mfg. (Prizer) that their 3 speed motors are not compatible with variable speed controls, and advised against it. They stated shorter motor life, and humming were two possibilities, besides voiding the warranty... "

feisty68 -- My husband is 5'8". In the store, he tried standing next to a 24" deep hood mounted at 29" high, with his shoes on. His fluffy hair touched the hood when he bent forward. So we decide that if we mount the hood at 30" high, he should definitely be fine.

Now, if we can get the 27" deep hood, we might need to mount it slightly higher than 30". I will try using kaseki's method to find out. :)

``People bend over to get their heads under hoods, so a stick figure cartoon will help reveal what hood height is sufficient to avoid bumps."'

This post was edited by ILoveCookie on Wed, Mar 26, 14 at 12:22

ILoveCookie, I know that Sone ratings need to be taken with a grain of salt, but does it concern you that Blue Star hoods don't have published Sone ratings? I have a hood that does a pretty good job of ventilating at 320-560 CFM - but I hate using it because of the noise (4.5-9.5 Sones).

And the Pfizer hood that you linked to - the fans that they make for that hood shroud only go up to CFM600 in the 36". Unless I am missing something?

This post was edited by feisty68 on Wed, Mar 26, 14 at 12:48

While making your decisions about hood height, do remember to pretend cook beneath it. There's a big difference in the way one stands to cook and the way one stands when a looming presence is threatening! In real life, one is used to the hood and not intimidated, so doesn't square up to it, and no one is looking the top of the backsplash in the eye except while scouring splatter spots. I don't hear about tall guys bumping their heads until they're at least 6'5". :) Not that it can't happen--just be sure what you need, rather than being intimidated.

Oh, and if you're worried about just walking by, my sincerely too low garage door put the bent down part of my new tailgate into the headbopping range, and it only took getting bopped a couple of times to learn to duck without thinking about it. :)

I know enough physics to follow Kas most of the time, but I know more about IRL cooking than the science. I have been chopping an onion on the island about six feet away from the draw zone of my 1200 cfm hood, with nothing cooking, and used the hood to suck the onion fumes out of the air. It works. Maybe not 100%, but enough to take it from tear gas to smells like good dinner.

I don't think that chef height is too much of an issue for the OP. Here's a drawing using 30" Bluestar RNB dimensions, with the range trim adjusted to the recommended 11/18" height over the counter surface (36" above floor in this case). I don't want to threadjack so I will be taking further commentary about chef height/hood depth to my thread.

feisty68, thank you for the drawing! It's very helpful.

``The Pfizer hood that you linked to - the fans that they make for that hood shroud only go up to CFM600 in the 36". Unless I am missing something?"

Hmmm. The 1200cfm fan option is indeed only listed under 48"+ Prizer hood. However, my sales person was able to quote 42" Prizer hood with 1200cfm internal blower for the 36" RNB that I was originally considering. I am going to double check.

I prefer the rounded front bottom edge of the Prizer hood, over the square edge of BlueStar. But if turns out Prizer doesn't do 1200cfm for the 36", then I will probably just go with BlueStar.

RE: noise level -- I haven't read much noise related complaint about Prizer / BlueStar hoods, so I guess it's on the reasonably loud side? Or maybe all the owners are so happy with the performance that the noise issue is negligible?

I haven't lived with a quiet vent, and don't really expect my new vent to be quiet either. I guess there is a difference between reasonably loud and intolerably loud, but as long as I can still hear my phone ring (inside the kitchen), I think it will be good enough. If husband needs to tell me something when I am attending the stove, he could always come closer...

pillog:

The onion chopping ten feet away from the hood can be expected to fill the kitchen air volume with fumes that the 1200 cfm hood removes at a rate that roughly depends on the actual air flow rate and the volume of the kitchen, or house, depending on how open the kitchen is. Sixty seconds of chopping may represent a few air-change periods by itself, thereby significantly diluting the onion odor by temporal exponential decay without us having to deal with any near-field hood flow patterns and their capture and containment interactions with hot rising effluent.

kas

RE: fan options for 36" Prizer Incline Wall Mount hood

``The Pfizer hood that you linked to - the fans that they make for that hood shroud only go up to CFM600 in the 36". Unless I am missing something?"

I contacted Prizer, and found out that the 36" is compatible with 1200CFM internal blower. This combination is not listed in their spec because most people don't need such a powerful vent.

I also found out that Prizer can build the Incline Wall Mount hood that I want at 27" depth. :)

This post was edited by ILoveCookie on Thu, Mar 27, 14 at 13:20

Okay, Kas, I usually follow you, but I'm totally lost in that last paragraph. My overall feeling is that you meant the fumes might dissipate by themselves in the volume of air in the kitchen. I don't know enough about the physics, nor the distribution properties of onion fumes to follow.

What I know is (not for the first time) I chopped half an onion on the island, about 6 feet from the center of under the hood, with myself between the two. I could barely get through the half from tearing up. So I turned on the hood (which I needed to for the saute, anyway). When I went back to do the other half of the onion, unlike when I don't turn on the hood, there was no tearing, and I was able to chop the second half, with the hood drawing, without tearing up again. Since it was the same onion, and the tearing only gets worse as the onion warms up, I'm going to continue to believe that the hood makes the difference. Maybe it's just circulating the air to make the fumes dissipate faster--maybe that's what you were saying!--but whatever it is that it does, the onion smell and tear fumes were gone, and the landscaper was commenting about smelling it outside, but not when he came into the kitchen. So however it works, it's a good thing, and I'm satisfied. :)

No no, I wasn't saying that, nor was I saying that the hood wasn't removing the onion fumes. I was saying that it removes those fumes pretty much as it removes any fumes that are introduced into the kitchen air, by removing the kitchen air at.X cubic feet per minute. When enough kitchen air has been replaced, the onion is hard to smell. During the cutting, depending on the flow paths of the air (rarely uniform), heavy onion oils may be swept out faster near the hood than if they had the dilution rate (molecular velocity) into the kitchen air that, say, gasoline, would have.

kas

Oh! Thanks for the explanation, Kas. I was totally lost, but I understand the translation. :) And I was thinking that the onion didn't disperse that much, and totally get the "heavy" and lower dilution rate. That makes a lot of sense if one knows onions. :)

And another endorsement for the powerful hood. :) Because we use far more onions in the kitchen than gasoline. :D

I don't think one can have too much ventilation. I went with 1000 cfm over my 36" RNB with griddle, thinking it would be more then enough. Turns out, it is adequate, but I often wonder what 1400 cfm would have been like?
BTW, my 36"x27" is mounted 36" above my range and works just fine with no head knocking, or sight problems...

This post was edited by ctycdm on Thu, Mar 27, 14 at 22:44

I just wanted to add my experience with my 30" RNB and Kobe hood. It's the same one feisty68 posted. 36" with 760 CFM. The hood is vented with 6" smooth wall pipe with one 45 degree offset straight up through the roof. I'd estimate 6' of pipe.

With typical cooking of boiling, light frying, etc, it does a decent job. Anything smokey like bacon or heaven forbid woking will just fill up the house. You can see the smoke just rise up, out and over the front edge of the hood.

So after reading other people's input, if you plan on doing any woking, searing, or char broiling, you can pretty much never have enough CFM to pull out all the smoke. You can only hope to minimize it, and from my experience 760 CFM is not sufficient.

Ventilation for powerful ranges is a sticky subject. On one hand, you don't want to stink up your house. On the other hand, you are often going to run into consequences if you try to exhaust that much air, especially in a cold climate. With no makeup air, those consequences can range from discomfort while cooking to asphyxiation. Powered, heated makeup air is expensive to buy and run.

The kitchen/appliance people say more CFM is better. They ignore the effects powerful hoods can have on the rest of the house.

The HVAC/building science people say less CFM is better. They ignore the desire to maintain a clean kitchen and an odor free house.

You have to decide which camp you fall into. Usually the sensible thing is compromise and do it Goldilocks style. Not too much CFM nor to little.

It is possible to have your cake and and eat it too, but that often ends up costing far more than most people factor into their kitchen budget for ventilation.

HVTech42 is right, of course. One has to choose where in the trade space of odor vs. CFM vs. MUA approach one wants to live and pay for. I've suggested before a maxim: Affordability, performance, aesthetics -- pick any two. Affordability, normally considered as the cost of the hood and related parts also includes recurrent costs. Conditioned MUA is certainly a recurrent cost, but fortunately one that should for most of us only occurs when both the inside to outside temperature difference is high, and heavy duty cooking is in progress.

In my pursuit of MUA, the most difficult aspects were finding appropriate places for the components making up the path and dealing with CFM control issues for my more complex situation. (Full disclosure: Multiple seemingly never ending renovations extending from the kitchen to interior areas to deck and yard areas have interfered with my completion of the control portion of my MUA system, so I have been unable to report on its design or level of success.)

kas

Thank you for sharing your experience EcoCheap! How disappointing for you. It sounds like the issue may be largely related to capture area? You mention smoke billowing outside of the hood area. The hood is only 22" deep. I realize it may be too late for your installation, but do you think it would have helped if your hood was built out from the wall? Of course, that may require installing it higher as well to avoid head bumping. (See my diagram posted Mar 26, 14 at 13:30)

I hope that bumping out that same hood will work for us because it just doesn't make sense for us to have higher CFM in a condo. But I am so tired of the smoke detector going off! We still don't have a hood installed!

Perhaps my post wasn't as thoughtfully constructed as it should have been. The following comments on makeup air were very good points to consider. I think the best take away is that for a reasonable setup, you can't expect heavy smoke to just funnel up into the hood and out. I'm just trying to set expectations a bit more reasonably.

Feisty, I thought you had chosen a different hood and had one by now. I know how long and frustrating the process can be, so hang in there. I don't think bumping out the hood will help that much. There seems to be a cone from which vapors get entrained and evacuated. The cone tip starts at your baffles and spreads out. Once you leave that cone, it doesn't get pulled in. So the smoke that doesn't make it into the cone rises up to the lip of the hood where there isn't any real flow towards the baffles, and some spills over on the outside. It's really disappointing to see that smoke just hit the hood and bounce out.

That said, moving it out further can only help. I'm not sure how you plan on achieving that. Do you plan on building out the wall behind the hood and then having some kind of trim to cover it? I would assume you'd want the hood flush with your cabinet box or door, so that would require those to be built out too.

Maybe I should start a post on my experience with the Kobe hood, but I think the audience would be small. The hood looks great. It is stainless steel, so it will scratch easily. The knockout for the electrical connection didn't actually get perforated, so our contractors cursed the thing as they tried to hack that hole open. It's not as quiet as I thought it would be, but it is acceptable. My sister commented on how quiet she thought it was though. The LED lights flicker if the fans aren't on. That's not a big deal since I don't know when I'd just have the lights on. There are two baffles and two spacers to install under the hood for the 36" model. It's not clear whether placing the spacers in the center (baffles all the way to the edge of the hood) or spacers to the edge (baffles in the center of the hood) provides the best performance. The instructions aren't clear about this. Placing them close together may increase the power of that cone I described to pull in smoke. Spreading them apart may increase the capture area but reduce that capture power or velocity.

Overall, the hood looks nice and has nice features. It's not a dream, but it's the best option I could find for our situation.

Thank you EcoCheap! Your experience is extremely helpful. I'm not sure if we have a better option than the hood that you bought. MUA has to be opening the window - we're in a multifamily condo so elaborate venting schemes are not going to happen.

"Do you plan on building out the wall behind the hood and then having some kind of trim to cover it? I would assume you'd want the hood flush with your cabinet box or door, so that would require those to be built out too."

I am planning on building out the wall and covering with trim painted to match wall (?). We don't have wall cabinets on either side so that's not really a consideration. The hood will also be close to the 8' ceiling so support for it may be partially ceiling mounted (?).

MUA has to be opening the window - we're in a multifamily condo so elaborate venting schemes are not going to happen.

If you're pulling a permit on this, you don't get the final word on what is and isn't going to happen - the inspector does. Code does not allow opening a window for a makeup air. According to them you either need to downsize the hood and live with inadequate ventilation on a powerful range, or downsize both the hood and the range.

If you're not pulling a permit or live in an area where they don't enforce that code, disregard the above, but be careful nonetheless. Makeup air is in the code because it is a safety issue.

Actually, disregard the part about inspectors - I just read your earlier post and I see you already have the range and it looks like you're just replacing the hood, not a full-on renovation. Still - tread with caution.

Thanks hvtech42. We are not pulling a permit. I'm not sure what regulations apply here, but I do know that there is no safety issue regarding MUA in this home. We have radiant floor heating, not anything furnace-like. Hot water is supplied remotely from a distant boiler. No ducting or ventilation except for the bathroom fans.

That's good to hear. Hopefully no fireplaces either. I did a similar thing in my own house. 600 CFM hood, no makeup air, no permit. Works great. I knew my house could handle it easily, but I do get worried whenever I see someone else talk about skipping it. I just want to make sure people are aware of the potential issues, which it seems like you are. Sadly not everyone else is and makeup air is a tempting thing to bypass because of the cost.

Nope no fireplaces. I learned a lot about this whole topic thanks to the awesome information and patient replies offered here on GW :) .

I went w/a Prizer 42" w/1200 cfm dual blowers (2 600 cfm's) over my 36" RNB w/griddle. When wokking or searing meat I most definitely have the blower cranked all the way and feel it's just adequate to pull most of the smoke from around the cooktop. I say most because I still get grease build-up on the front and top of the hood, it's only 24" deep, a 27" would do a better job. I'm 6"2 and once in a while bump my head on it but like mentioned above most of the time I'm bent a bit so it's not an issue (especially if I'm paying attention). I turn it on ~ 5 minutes before I start to get the flow going when doing something on hi heat. I don't think anything will be perfect, it's a combination of sucking up as much as you can and cleaning up what doesn't make it into the blower ASAP. I wipe down the exterior once a week, put the baffles in the DW every other week and deep clean it about every 6 weeks. These hi power ranges create a lot of mess, diligent cleaning s/b part of the kitchen routine.

Thanks Mistman - that gives a realistic idea of how much CFM is really required to deal with searing/wokking.

I've been contemplating many of these issues in my kitchen redesign and the issue of heated makeup air seems the most challenging to me. The only solution I'm aware of is from Electro Industries, and that supposedly is very expensive and requires an 80 amp breaker (which probably would require a service upgrade). The building inspector in my town doesn't require makeup air for residential installations, so I'm tempted just to go with the open window approach.

Electric MUA heating should scale with the flow rate that it has to deal with at the temperature delta that it has to overcome. For high flow rates this can be quite a few kW. However, a self-contained heater such as Greenheck sells will be the least complex approach.

Another approach, suitable when one has a boiler and hot water baseboard heating, is to use a hot water fed heat exchanger (looks much like an automobile radiator) controlled by a circulating pump that is triggered by thermostats. I have this setup. One thermostat sensor is in the air space below the heat exchanger to measure the temperature of the air put into the house (MUA feeds into ceiling from attic), and a lower setting thermostat is attached to the heat exchanger copper plumbing to force circuit heating if the attic is cold enough to risk water freezing. The two thermostats are operated in an OR circuit for control of the water pump via the furnace/pump controller logic that prioritizes my many circulator zones.

For those with gas heat, it may be sufficient for the lower range of cfm to trigger ON the furnace when the air temperature at the MUA outlet falls below some value, thereby getting a head start on warming the air. Most furnaces are designed for normal house heat losses, so won't be sufficient for the 1200 cfm MUA cases, but may well work when the flow rates are in the 450 regime. Also, electric toe kick heaters installed in the kitchen (if MUA is introduced directly into the kitchen) may be another solution.

Other, more industrial solutions come to mind, but probably wouldn't fit well with modern kitchen styles.

kas

Thanks Kas. I do have a boiler and baseboard heating. Does any heat escape from the heat exchanger into the attic? My concern would be that it might cause ice dams in the winter.

Well, "any" is potentially a very small amount, and I'm sure that there is some slight amount. My attic, however, is vented all around the periphery, at the ridge, and also with an attic fan housing. Ice dams at the roof edges tend to occur when the outside air warms up during the day and heats the snow bottom up through the vents instead of top down.

In my present half-completed configuration, the ~ 2 x 2 ft heat exchanger sits above a Cooley and Hart 3 x 3 diffuser in a hall ceiling. There is a furnace filter taped down on top of the heat exchanger. This style of filter (Honeywell Filtrete) needs significant pressure drop to move much air through it, and I was pleased to observe that warm air doesn't seem to rise through it in the winter, or hot attic air settle through it in the summer. The sides of the heat exchanger and its plumbing are buried in insulation.

When kitchen fans are running and the house is closed up, air is pulled through and the thermostats, the larger-than-typical-size Taco pump, and the furnace controls do their thing to heat the air. (The circuit is capable of well over 100k BTU/hr depending on furnace and air temperature.)

The problem, as I have pointed out a few times here, is that pulling air through a filter and heat exchanger requires a pressure drop -- a drop too large for combustion appliance safety. My only combustion appliance is an oil furnace, and it now uses its own MUA system to avoid back-drafting. Nevertheless, if I were to run both kitchen fans at once at full power expecting all flow to be made up through the heat exchanger without fan boost (possibly 1400 actual cfm with restricted MUA), the pressure drop in the house causes some furnace exhaust to be pulled into the house via tiny cracks not normally relevant when there is a positive draft, so I don't do dat without an opened window.

My intention is to duct the heat exchanger to a mushroom air intake already installed on my roof via an axial in-line fan and a four-inch pleated filter caddy so that at the maximum possible flow rate (possibly 2000 cfm, say) the house pressure can be balanced and all the MUA comes from outside without mingling with the attic air. A damper may be needed, although as noted, the Filtrete coating will be pretty resistant to air passage without some deliberate pressure drop from the in-line fan.

kas

ILoveCookie, what hood did you end up going with? Can you share your experience with it - esp noise and function? I'm still researching hoods (rolling eyes).

i am so new to all of this. i'm moving to a new home, renovating, and will be purchasing a 36" 6 burner range with 2 20k BTU burners. haven't decided yet... BS? thermado? but my question is, how do i know if MUA will be an issue? i live in NC, zone 7. thanks!

lilmagil1, you may want to start a new thread with your questions :) .

thank you kaseki :)

I just wanted to cross link a helpful Hood FAQ page for readers who are finding this thread helpful for reference years later. You'll find even more helpful advice about adequate venting at this additional thread here, and be sure to read through the comments section as well: https://www.gardenweb.com/discussions/5161173/hood-faq#23472242

That link is so helpful! Thank you very much for sharing.