Hi,
I am in the process of adding Central Air to our home. It will be an attic install and will need everything from a trunk, return, and ducting. I have done a lot of reading and research online, and have come to the conclusion the most correct information is in Manual J and Manual D to make sure the system is sized correctly and the right ducts are chosen.
I have also learned there are a lot of seat of the pants contractors who use rules of thumb. I want to protect myself and verify that what ever recommendations I get are at least close to proper (which I guess would require me knowing the rules of thumb).
The house is ~1300 sg ft. I know the rule of thumb for this size house in MD is ~2.5 Ton, but there are some additional factors, like we have a sun porch facing north, so I assume having 30 feet of windows will affect the tonnage size, and may put me at 3 ton or more?
Also, it seems like some contractors will just use flex duct for ease of install, is this bad or should I require a trunk with metal take offs?
Seems like the rules of thumb I have found are the duct CFM should match the room sq ft, the duct velocity should not exceed 600 FPM, and you do not want to over size the system to prevent short cycling and get a cool clammy home.
How concerned should I be about getting the most accurate system, it seems like there might be a lot of wiggle room in sizing and ducting, and the main drawback is you might lose some efficiency.
Also, should every bedroom require a return? I have seen retro fit installs where there is no return in the bedroom.
Any help would be greatly appreciated!
Jim
I am in the process of adding Central Air to our home. It will be an attic install and will need everything from a trunk, return, and ducting. I have done a lot of reading and research online, and have come to the conclusion the most correct information is in Manual J and Manual D to make sure the system is sized correctly and the right ducts are chosen.
I have also learned there are a lot of seat of the pants contractors who use rules of thumb. I want to protect myself and verify that what ever recommendations I get are at least close to proper (which I guess would require me knowing the rules of thumb).
The house is ~1300 sg ft. I know the rule of thumb for this size house in MD is ~2.5 Ton, but there are some additional factors, like we have a sun porch facing north, so I assume having 30 feet of windows will affect the tonnage size, and may put me at 3 ton or more?
Also, it seems like some contractors will just use flex duct for ease of install, is this bad or should I require a trunk with metal take offs?
Seems like the rules of thumb I have found are the duct CFM should match the room sq ft, the duct velocity should not exceed 600 FPM, and you do not want to over size the system to prevent short cycling and get a cool clammy home.
How concerned should I be about getting the most accurate system, it seems like there might be a lot of wiggle room in sizing and ducting, and the main drawback is you might lose some efficiency.
Also, should every bedroom require a return? I have seen retro fit installs where there is no return in the bedroom.
Any help would be greatly appreciated!
Jim
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