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I like to convert a window A/C unit into something like a central A/C. The unit I have has a standard Return Air grill and an Out-Put grill. It is Kenmore and has touch pad controls. I would build 2 boxes to match the surface area of each grills. Each box will have 2 insulated flex ducts (4 inches dia.), return and supply for 2 bedrooms. Each duct will be no longer than 6 feet. I would put this A/C in the attic and attach it to the window there. There will be a drain pan. I thought I can do this as long as I don’t restrict the volumn of air for return and supply. I figured that going up to the attic to turn it off and on would be small price to pay. Is this feasible? Will the hot air in attic do something to the unit, both when it is being used and not used? Will using 4 inch duct restrict the air movement and blow out the motor or condenser or make the unit inefficient? Thank you to all and I am looking forward to hearing from all the tinkerers.
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You don't say how many BTUs the unit is and even for a small unit, sending several hundred cfm of air down 2, 4 inch ducts is really pushing it. The other problem is the heat being dumped into your attic. Unless you have a way to get the heat out there, the air conditioner is not going to work very well. Air conditioner efficiency really goes into the tank when the outside air temperature goes significantly above 100 degrees F. Attics easily exceed 120 F and with your air conditioner dumping the heat from the bedrooms up there it is going to go much higher. Up the duct size to at least 8 inches and provide an attic fan to get rid of the heat before you launch this project.
*Kwan - Many window air conditioners today are designed to take the condensate that collects in the drain pan and blow it into the cooling coils. The configuration you describe may leak into the room below. Plus you are fighting static pressure forcing the air into small ducts as noted.Jeffb Been there, done that, mopped it up
*Kwan, Go for it! I've been considering a similar project and would like to know how it works.One consideration I had was any step down in the size of air in or out. I was going to make the runs as short as possible. My main interest was to get that loud machine a little farther from the room. Let me know how it works out.Skip
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Thank you all for the suggestions. I found out a bit more. The a/c is 9100 Btu. I called the factory but there is no technician at hand. It may move 250 cfm. My reasoning was that the face grill size would tell me the duct needed. The return side (inches) is 16 by 12 and supply side is 6 by 12. I will use at least 8 inch sheet metal duct. It does splash condensate. That's another problem to think about. Anyway, I am starting an addition and this will be a project for next year. Again, thank you.
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I like to convert a window A/C unit into something like a central A/C. The unit I have has a standard Return Air grill and an Out-Put grill. It is Kenmore and has touch pad controls. I would build 2 boxes to match the surface area of each grills. Each box will have 2 insulated flex ducts (4 inches dia.), return and supply for 2 bedrooms. Each duct will be no longer than 6 feet. I would put this A/C in the attic and attach it to the window there. There will be a drain pan. I thought I can do this as long as I don't restrict the volumn of air for return and supply. I figured that going up to the attic to turn it off and on would be small price to pay. Is this feasible? Will the hot air in attic do something to the unit, both when it is being used and not used? Will using 4 inch duct restrict the air movement and blow out the motor or condenser or make the unit inefficient? Thank you to all and I am looking forward to hearing from all the tinkerers.