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  1. #27
    Join Date
    Aug 2003
    Posts
    626
    Forced air HVAC filters, are in place to keep the air handler coil clean. This is the reason the filter is there. A filter at the air handler does NOT depend on non leaky ducts to filter the air before the air reaches the coil. Filter grill filters HAVE to have air tight returns to be effective.

  2. #28
    Join Date
    Nov 2005
    Posts
    35
    Very true!

    Filter grill filters HAVE to have air tight returns to be 100% effective.

    Filters at the return grills certainly do nothing to the leakage.

    Whatever the percentage of the leakage in the total intake air flow is, say x%, filters at the return grills only effect 100-x% of the entire flow. Some thing is still better than nothing.

    Leakage exists everywhere. We can only hope that x < 50.

  3. #29
    Join Date
    Nov 2005
    Posts
    35
    uktra,

    Just in case you’ve missed my earlier posts. The “thin” filters at the return grill are an addition to the filter at the main unit, not a replacement of it.

  4. #30
    Join Date
    Aug 2003
    Posts
    626
    Dual filters are not need to keep the coil clean, and as mentioned before can cause problems.

  5. #31
    Join Date
    Nov 2005
    Posts
    35
    Very true!

    The purpose of the air filters at the return grill is to keep return duct clean, or at least help keeping the return duct clean a little so that duct cleaning isn’t or less needed.

    Most filters can catch 90% or more dust. Say someone clean duct once every 3 or 5 or 10 years, using a filter at the return grill may allow it go for 20 or 50 years.

    Yes, dual filters can cause problems. Dirty duct can cause problems too. I guess we’ll just have exercise the god given right to choose and pick one to live with.

    As I said earlier, a HVAC system is like a breathing elephant in our homes. The duct work is the long trunk of the elephant, much longer and complicated than the real thing. Maybe the most of us don't mind dirty duct at all. The fact is that a small duct cleaning industry exists. I do believe most system have enough engineering margins to handle the extra restriction of a few filters at the return grill. If not, the filter at the main unit better be replaced VERY frequently, since a dirty filter causes restrictions too.

  6. #32
    Join Date
    Nov 2005
    Location
    On Tour or Central FL or Michigan
    Posts
    49
    Good luck on your quest for this new product and system. As I've seen noted here, most of the professionals seem more interested in the filter protecting the equipment. Keeping the air clean is only a side benefite.

    Adding a filder at the return grills will likely increase the duct leakage due to the likely restriction of air flow through the return grill. Therefore, somewhat defeating the purpose of the filters at the return grills. The ductwork would need to be very well sealed. The ductwork and return grill size might need to be bigger to cope with the restricted flow.

    The assumption that existing buildings are overengineered enought to cope with the extra restriction may be rather optamistic. The impression I have gotten on thsi forum is that duct systems are more often undersized.

  7. #33
    Join Date
    Nov 2005
    Posts
    35
    Thanks.

    I agree with you on the leakage. I hope the leakage is a small percentage of the total air intake.

    Your impression may very well be the fact. That’s why I plan to sell it to the luxury new constructions first. A few hundreds bucks give them something to talk to their customers for 5 extra minutes.

    My plan is to make the minimal changes to the traditional return grill to allow the option of taking a filter. Minimum change will preserve the tradition appearances of the return grill, easier to be accepted and keep my cost as well as my customers’ cost low. Minimum change and preserving the tradition appearances will make my thing a replacement of what people already have. I’ll also try to sell it to hospitals, hotels and office buildings.

    Since I guess not many people have their duct cleaned more than once, I’ll try to sell it to the duct cleaners. I’ll help them expand their market by providing them a way to help their customers keep a cleaned duct clean so that cleaning makes more sense.

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