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Thread: Dryer Booster fans ?

  1. #31
    DIY Junior Member Chris in Dallas's Avatar
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    If the fan motor is turning, the blades are turning. It may be that the booster is working against pressure, and is not able to reach a rate of airflow that you can feel. Additionally, the lint screen box may be leaky.

    Regarding tight homes needing air exchanges, that is definitely true. But it is ideal to control the rate of those changes, and to filter and condition the outside air as it enters the house. An HRV in a tightly sealed house allows that. The humid air entering from outside will still be dried out by your AC system before it goes to the dryer, so, one way or another, changing the RH of that air to absorb moisture from the clothing is accomplished.

  2. #32
    General Engineering Contractor ballvalve's Avatar
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    I like the pipe in a pipe idea to scavenge the waste heat and bring in make up air. I do it with a Polaris water heater. But you might have a serious condensation issue at certain times. Better use aluminum pipe.

  3. #33
    DIY Junior Member Chris in Dallas's Avatar
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    If I'd stuck with the coaxial pipe idea, I'd have switched to an 8" outside pipe to be sure to have very little resistance on the intake side. But because I would have to insulate the whole thing anyway, I just went with 1.5" duct board, and cut it to fit very tightly between my ceiling joists (it extends beyond the top of the joists). Here in Dallas, condensation should only occur during a few times a year, so I just sloped the exhaust pipe down from the beginning of the duct board heat exchanger to the vent outside, and put the seam up.

  4. #34
    DIY Member Agu's Avatar
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    Solved the problem with the malfunctioning FanTech. Turns out the increased air velocity moved old lint in the ductwork down the pipe until the duct clogged. Pushed a drain cleaner snake up the outlet from outside about ten feet and knocked loose a huge ball of lint.

    Showed the Mrs the ball of lint and she responded, "That's the biggest chunk of belly button lint I've ever seen." I just threw it in the trash and shut up .....

  5. #35
    DIY Junior Member Chris in Dallas's Avatar
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    Update on my modified dryer venting: Finished the system, installing a gravity-operated damper on the intake, insulated all the ducts, and still working just great. Lots of velocity at the exit, full loads dry in 40-50 minutes. So, I can tentatively recommend this type of system, though it adds expense, and is detail-intensive. I've not needed any boosting for either the intake or the exhaust, and that is probably at least partially because this modern dryer seems to have a high-capacity exhaust fan. The manual lists acceptable equivalent duct runs that far exceed the typical recommended run of 25'.

    I'm a bit taken aback still by what I consider unwarranted negativity regarding the design, and I think that negativity comes from a failure to understand the mechanism and assumptions, as well as the common reactionary aversion to innovation and breach of convention. I've dealt with that a lot, particularly from engineers approaching retirement. Maybe I'll be like that one day, too.

  6. #36
    Retired Defense Industry Engineer jadnashua's Avatar
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    Industry standards for free air makeup on a gas appliance are fairly well estabilished...you don't have that. Regardless, it's your house, and if it works, fine for you. there may be situations where it doesn't, as the standards are set to cover many contingencies, which you may never experience, or have yet to experience. What works in one situation, may not work for all. Providing unconditioned combustion air to a gas appliance is a good way to save money, but it has to be designed properly.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #37
    DIY Junior Member Chris in Dallas's Avatar
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    Code dictates that when a combustion appliance draws air through a duct directly from the outside, an opening of 2 sq in per 4 kbtu/h is required. A dryer produces less than 40 kbtu/hr, so only 20 sq. in are required. My 6" duct provides 28 square inches. BUT, more importantly, the combustion air for a dryer is not supplied passively, which is what that particular code is written for. More relevantly, for forced air combustion appliances, code dictates that all of 1 cfm of outdoor air is required for every 2400 btu/hr. So for 40 kbtu/hr, that comes out to all of 17 cfm. A dryer PULLS 150 cfm or so of air through the cabinet.

    Incomplete combustion is almost completely impossible.

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