Heating, Air Conditioning, Fridge, HVAC/Bath vent

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Question
Thank you for taking the time to help with my problem.

I have two bath fans that are exhausted through one roof vent. The two flexible ducts join at a tee at the roof. Although both fans have dampers (that are moving freely and not stuck closed or open), when only one fan is in use, some exhaust air is coming in through the other fan. Adding a second roof vent is a possibility, but I would prefer to cut as few holes in my roof as possible. Could I add two dampers right at the tee by the roof? I have seen two types; one is all metal, the other is a metal frame with a plastic/fabric "sock" inside that only permits airflow in one direction. This is a link to the second type:

http://www.tamtech.com/store/one-way-air-flow-valve-6-duct-bath-fan-range-hood-e

Do you think that either damper set-up would help? If so, do you think the second type is worth the money for this application? Thanks again for your help.

Answer
John,

I recently installed a system similar to your application in my residence, I did not care if I was drawing air from my other bathroom when that bathroom was not in use, I took my total cfm of both bathrooms and bought one that handled both rooms. It was not important that both dampers opened when using one room. The sock type looks  to be a back draft type check valve type ,doubt that they would work. The only way a setup ( that you and I have ), would be to use two powered motorized dampers. Just isn't practical. The instruction that came with my bathroom kit ,did not mention as an option some type of isolation damper to run either or .

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Joe

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40+ years diversified experience.An HVAC/Refrigeration Self Employed Contractor since 1986. NATE Certifield. Answer questions pertaining to Residential and Commercial Air Conditioning , Warm Air Heating, Heat Pump systems.Mechanical and Electrical troubleshooting of these systems.Be as detailed as possible when describing problem.Packaged unit or split systems.No appliance questions.

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Installation and Troubleshooting, Mechanical and Electrical, in following areas, Refrigeration ( Walk In and Reach In Coolers and Freezers ) Commercial Roof Top and Packaged Heating/Cooling ( Natural Gas,Propane, Electric, and Heat Pumps ) Computer Room Air Conditoning Systems,Commercial Residential Packaged and Split Systems Air Conditoning and Heat Pumps.Warm Air Oil , Natural and Propane Gas Heating systems.

Education/Credentials
Graduated from Private Technical School in 1975. An HVAC/Refrigeration Contractor . Have Unlimited Heating/Piping and Cooling Contractor License.Limited Sheetmetal Contractors License.NATE Certifield. York Certifield Master Heat Pump Technician 1986. Served 33 years combination Active Duty Air Force , Air Force Reserves and Air National Guard in the HVAC/Refrigeration Shop/Mechanical Shop. Troubleshooting/Installing HVAC/Refrigeration Equiptment Worldwide. Retiring in 2003 as a Senior NCO ,and a Mechanical Superintendent.

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