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Old 01-11-2010, 01:27 PM   #1
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makeup air


Boston area two storey home-Heat-lennox hydronic ----A/C american standard two stage condensr. variable speed air handler --air return top of stairs----- PROBLEM-kitchen gas stove range hood 500 cfm needs makeup air. What do you think of following----6" intake -insulated flex duct to electrically controlled damper (normally closed-power off) connected to AC return air plennum. When range hood is operating damper would open allowing make up air?????

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Old 01-11-2010, 03:23 PM   #2
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makeup air


Not enough air.

You aren't going to get 500 CFM through a 6", without putting the whole house into a high negative pressure.

Your hood probably isn't able to really do 500CFM. But you still need more then a 6".

8", if not a 10".

Of course. You should use the range hood sparingly. In winter, the average 2,000 sq ft house with 8" ceiling. Would be an ice box in less then 20 minutes with 500 CFM of fresh air coming in.

Make up air is best brought in near the appliance that needs it. Not through the whole house.

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Old 01-11-2010, 03:50 PM   #3
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Originally Posted by wmmurphy View Post
Boston area two storey home-Heat-lennox hydronic ----A/C american standard two stage condensr. variable speed air handler --air return top of stairs----- PROBLEM-kitchen gas stove range hood 500 cfm needs makeup air. What do you think of following----6" intake -insulated flex duct to electrically controlled damper (normally closed-power off) connected to AC return air plennum. When range hood is operating damper would open allowing make up air?????
Return air is not make up air. Make up air is outdoor air. Usually a small duct from the outside to the return air. Required by code in commercial systems. Now if you mean that to connect the 6 inch duct to the outside to the return air it may work, but only if the duct is a short run and connected very close to the fan coil. Otherwise an 8" size might be better.

Last edited by H. Phillips; 01-11-2010 at 03:52 PM.
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Old 01-11-2010, 03:55 PM   #4
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Originally Posted by beenthere View Post
Not enough air.

You aren't going to get 500 CFM through a 6", without putting the whole house into a high negative pressure.

Your hood probably isn't able to really do 500CFM. But you still need more then a 6".

8", if not a 10".

Of course. You should use the range hood sparingly. In winter, the average 2,000 sq ft house with 8" ceiling. Would be an ice box in less then 20 minutes with 500 CFM of fresh air coming in.

Make up air is best brought in near the appliance that needs it. Not through the whole house.

It probably is getting more than 500 CFM of infiltration on a windy day, at least with 500 CFM of outside air it will be presureized keeping out infiltration. However houses do not get 500 CFM of infiltration on calm days.
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