Fireplace and range hoods

[98kx1927]

Not sure if anyone can help, but I thought I'd ask anyway so bear with me

I'm remodeling my kitchen and will be putting in a very large gas cooktop that requires a 2000cfm range hood for ventilation. I've been reading up on the need for make up air when the hood is running.

The concern is that when the range hood runs and is pulling 2000cfm out of the house, there can be backdraft down the chimney and out my stove. Has anyone dealt with this issue before? See I did tie it into a fireplace . . .

I do have the results of a blower door test on my house before foaming the attic and crawl space, so I do have an idea of its leakiness. It is pretty leaky. I found a couple resources on the web as well:

(broken link removed to http://www.broan.com/tools-landing-page/make-up-air-damper-tool)
and
http://www.greenbuildingadvisor.com/blogs/dept/musings/makeup-air-range-hoods

Just looking for first hand experience with this issue. I'm not opposed to addressing the issue, just wondering if anyone here has had to deal with this issue themselves.

david

 

[begreen]

Are you sure that number is correct? Usually these units range from 600-1200 cfm. 2000 cfm is significantly higher than most central HVAC blowers. It will definitely pull air out of every orfice of the house that is not well sealed. Be sure you get a multiple speed unit as the noise at full speed will be loud. My SIL put in a large range and hood. They usually run the hood on the lowest speed. Their house is large and old. So far they have not had an issue with the fireplace but that is several rooms away and very rarely used.

 

[Oldman47]

2000 scfm is a good sized window fan/box fan. That seems wrong to me. Can your stove use a simple recirculation fan with a charcoal filter in it? That way you would not be exhausting huge amounts of heated air.

 

[BrotherBart]

Yep. Pro range hoods are 2000 cfm.

 

[begreen]

Don't wear a chef's hat near one of those 2000cfm range hoods. It will get sucked into it. Also, wear ear protectors while cooking.

 

[jaychino415]

David, I am currently running a 900 cfm ventilation hood and it creates a negative pressure in the house if i don't crack window s. It's worse when i have the fireplace going. Smoke comes back in the house and fire alarms go off. The house is super airtight. Thinking about installing a fireplace insert and OAK since there's a ash access door i can use.
Interesting place to put the make up air kit behind frig. in article, question is will it help with cooling frig. or add more dust to the frig. cooling coils. I think this idea is novel, but i wouldn't do it. More cleaning of coils and how often you planning to pull frig. out.

Good Luck! J

 

[Oldman47]

If you expect to get cold air in it should help cool down the cooling coils. What a novel approach. Someone was thinking in terms of whole house when they came up with that location.

 

[98kx1927]

I was considering a couple solutions.

Broan recommends connecting the MUA damper to the return air duct for the furnace. This would be very easy for me to do and kind of makes sense in that it would pull the air in through the HVAC system, not sure if you need a lock out on this. Don't want the HVAC system sucking outside air when the hood is running. I would put a filter on it prior to it entering the return air duct.

The other idea is to put two floor registers underneath the cabinet where the cook top is. The MUA duct would then connect to these registers. The idea would be that the MUA would flow up through the cabinets around the cook top and out the vent, taking the smoke with it. I'm not sure how well this would work or if it would it impact the cook top burners or not. The desire would be to have the outside air (unconditioned) be sent right back out the vent fan reducing the costs of conditioning it.

Or maybe I'm just over thinking it. The hood has 6 speeds, I don't even know if I would ever use the highest speed. I don't think that anything under 75% speed would need to even open the MUA damper. My house is fairly leaky even after foaming the attic and sealing the crawlspace.

 

[begreen]

If the full power of the range hood is very unlikely to ever be used or needed, why not get a less powerful hood?

 

[98kx1927]

Yes, using the lowest rate hood is the desire.

 

[Sparkster]

In areas that have adopted the 2009 IRC building code, it is spelled out.
Range Hoods – Exhaust hood systems capable of exhausting > 400 cfm shall be provided with make-up air approximately equivalent to the exhaust air rate and have automatic closers that start and operate with the exhaust system. [M1503.4]

 

[98kx1927]

Well my area has not, but I still want to do it.

I've sized my hood to be 3" wider on both sides than the rage (54" hood vs 48" cooktop), if I could find one that is 27" deep then I could probably drop the CFM and reduce the issue, though not eliminate it.

david

 

[Ski-Patroller]

Commercial Kitchen Hoods often have a makeup air unit installed with them, often with a plenum right next to the exhaust hood. They often have a makeup air heater installed also so they don't blow 10 deg outside air into the kitchen.

 

[glennm]

Mine can reverse the draft and pull smoke into the house on full speed if the conditions are right. Don't ask me how I know? I only ever run it on high if I have a lot of smoke from over cooking something. I just crack the kitchen window a bit and there is no problem when this happens. Low is all I need most of the time and that doesn't create any issues.