# Make up air



## Cougars32 (Mar 7, 2013)

We are installing a 900 CFM hood vent in a residential home and we are told we need to bring in 900 CFM of make up air. Any ideas of a system this size for residential homes?

Thanks,
Lloyd Martindale
C&K Custom Remodeling

www.CkCustomRemodeling.com


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## txgencon (Jan 4, 2011)

Seems like you're close to the threshhold of commercial kitchen equipment. 

It will be interesting to see if anyone can give you any specifics here.

Good luck.


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## duburban (Apr 10, 2008)

my old heat recovery system boss made a make up system for a fireplace that opening and blew in air only when the fire was burning or in your case when that fan is switched on. size vent and fan to 900 cfm?


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## beenthere (Mar 5, 2009)

Hope you have mild winters and summers. other wise you'll be needing 60,000 BTUs of heat for the make up in winter, and 2.5 tons of cooling for the make up in summer. This is in addition to the homes normal heat and cooling.

Sorry, I don't gt to any residential places where they have hoods this large, so I can't tell you anything about who to contact for a make up unit.


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## duburban (Apr 10, 2008)

is the house actually tight?


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## AccuGreenHP (Mar 7, 2012)

I think the first question should be: Why are you installing a 900 CFM range vent hood?


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## Cougars32 (Mar 7, 2013)

Thanks for comments. These homes are ultra tight and I know this because I have remodeled other homes in the neighborhood. The reason for this large of a unit is they cook with a lot of oil and they want the biggest CFM unit in the neighborhood. This is the largest I've been asked to install so I'm at a bit of a loss.


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## griz (Nov 26, 2009)

Problem with make up air I encountered on range vents is you will draw cold air into the home. This was quite objectionable in my case.

Typically one does not run a range hood for long periods of time. If cooking vapors are an issue it is very natural for the owners to just crack the kitchen window until the issue is resolved.

You are also going to have to wire in the make up air to come on automatically with the hood. If you fool with any of the factory wiring you will likely void any warranty.


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## Cougars32 (Mar 7, 2013)

*Thanks Griz*

I have been told the same things here in Portland. I have heard there is a way to bring the air into the existing heating / cooling system to control temperature but I have had trouble getting any HVAC guys willing to tackle the project.

I have also been told that we can use a negative pressure sensor vs wiring directly to the switch but I am still waiting for confirmation from the inspector. 

I'll try to post any information I find out here.

Lloyd Martindale 

www.CkCustomRemodeling.com


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## beenthere (Mar 5, 2009)

Cougars32 said:


> Thanks for comments. These homes are ultra tight and I know this because I have remodeled other homes in the neighborhood. The reason for this large of a unit is they cook with a lot of oil and they want the biggest CFM unit in the neighborhood. This is the largest I've been asked to install so I'm at a bit of a loss.


Ah, so they really don't need one that big, they just want to be ahead of the Jones.

Is the hood already ordered? If not, then just order one with its on make up air. 

No residential furnace is gonna do well with 900 CFM of outdoor air coming in. Specially when your area is at its lower outdoor temps. The A/C won't handle it either. 

On a 3600 sq ft house with 10 foot ceilings through out. That hood could exhaust 25% of the homes volume in 10 minutes.


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## Cougars32 (Mar 7, 2013)

Beenthere,

Great information, looks like I need to do some educating before ordering.

Lloyd Martindale

www.CkCustomRemodeling.com


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## Inner10 (Mar 12, 2009)

griz said:


> Problem with make up air I encountered on range vents is you will draw cold air into the home. This was quite objectionable in my case.
> 
> Typically one does not run a range hood for long periods of time. If cooking vapors are an issue it is very natural for the owners to just crack the kitchen window until the issue is resolved.
> 
> You are also going to have to wire in the make up air to come on automatically with the hood. If you fool with any of the factory wiring you will likely void any warranty.


That doesn't fly here...they make you install a big enough HRV for fans over something like 300cfm...Or something like that...not my area of expertise.


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## slowsol (Aug 27, 2005)

Talk with a commercial HVAC contractor. They do this type of thing everyday in commercial kitchens.


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## Eaglei (Aug 1, 2012)

I would tell them that for that size exhaust that they would need to consult with a HVAC engineer. On some of the higher end homes we work in the whole house is sized up by a mechanical engineer and HVAC together . I know if I was told that , I would'nt do it


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## flashheatingand (May 3, 2008)

Cougars32 said:


> We are installing a 900 CFM hood vent in a residential home and we are told we need to bring in 900 CFM of make up air. Any ideas of a system this size for residential homes?
> 
> Thanks,
> Lloyd Martindale
> ...


Who told you this? The building inspectors? or the manufacturers? If this was mandated by the inspectors, I suspect this was due to a commercial grade range. I


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## thom (Nov 3, 2006)

I did a few commercial kitchens. We used a single switch to power a contactor (relay) with a 110V coil. That will turn on the hood and make-up air at the same time. You can get the air with a typical squirrel cage blower, an evaporative cooler works just fine, leave off the water. 

The air needs to enter very near the hood. Preferably right at the range. 

Some commercial systems include the make-up air in the hood as was suggested earlier. You could do this and it would provide a better system.


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## ScipioAfricanus (Sep 13, 2008)

My personal opinion on this (for what it is worth), Thom has the right idea. I worked in many a commercial kitchen installing hoods, exhausts, blowers etc. and I always understood the idea to be to get the make-up air close to the hood so that the exhaust will take in the greasy vapor from the grill kitchen area only.
I think that we designed for the make-up air to be about 75-80% of the exhaust CFM.

Andy.


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## thom (Nov 3, 2006)

You might try a power activated damper directly behind the range below the hood. This should allow enough air without the power to run a powered vent. I've never seen it done this way but it should work as long as the opening for the vent is large enough.


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## beenthere (Mar 5, 2009)

ScipioAfricanus said:


> My personal opinion on this (for what it is worth), Thom has the right idea. I worked in many a commercial kitchen installing hoods, exhausts, blowers etc. and I always understood the idea to be to get the make-up air close to the hood so that the exhaust will take in the greasy vapor from the grill kitchen area only.
> I think that we designed for the make-up air to be about 75-80% of the exhaust CFM.
> 
> Andy.


The other 20 to 25% came from the min fresh air that the units for the rest of the restaurant were set to. 

In a tight house, he may not have enough leakage to make up the rest of the air.


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## Hardly Working (Apr 7, 2005)

Wow this is becoming a pretty good thread.

I called my HVAC guy today (that's an Eng.) and after spewing all kinds of math calcs. at me he said wait till they get the heating bill. You not only need make up air but heated make up air. If it's in the 30's it wont take long to cool that house down in just a few minutes. We're talking an extra 45K of BTU in addition to what the house already has. 

This can also become an issue when it comes to reselling the house. Is the new homeowner really going to want to spend an extra $30 to cook dinner when they turn the hood on? If it's drawing that much air it's more than likely to suck up grease vapor and collect in the hood. Now let's think safety and fire suppression. He said you could be talking between $4-$12 per CFM. Tell the HO to stop shopping at the discount restaurant supply. 500 CFM should be fine he said.

With that said I no nothing about HVAC. That's why I call him! Basically you've got a big can of worms there. Best of luck and let us know how it turns out.


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