HVAC seeking to boost air

B > Trying to remedy a rube goldberg duct work system that results in, ..., B > less than optimal air flow to the far end of a run. What I can determine B > by eye, tape, and feeling around up inside the duct looks like this: B > B > * GMPN080-4 furnace/AC, plenum & duct work originally serving 1288 sq ft B > * All original branches used top take offs & 6" flex pipe - all work fine B > * Two long runs into garage/workshop area were added later - 576 sq ft B > * Each run to 3 4x12 registers spaced above windows & along outside walls B > B > The concerns I have with one particular run are all the twists and turns an
B > I know thats killing the air flow. I make it about 65 feet but I know each B > change in direction makes it seem like more. How much more I don't know... B > B > * Top take off to 18 ft of 7" flex pipe between floor joists B > * Then to a metal 90 and 5 ft of 7" flex pipe across the bottom of the jois s B > * Then to a metal 7" round to 7" oval straight boot B > * Then to 2 vertical 45s 7" ovals to get back up inside the joists B > * Then to a 90 and 10 feet up inside the wall cavity with 7" oval B > * Then to another 90 to get horizontal again B > * Then to a 7" oval to 7" straight boot B > * Then 24 ft (or so) straight 7" metal pipe with 2 of the registers B > * Then a 90 to 8 more feet of straight pipe with 1 of the registers B > B > I can't see any other way to have done the ducts given the constraints of B > joists / walls / register locations. I can see 3 different things to try: B > B > 1) get rid of the flex duct and go all metal (reduce resistance ?) B > 2) install an in duct aux fan in basement and/or out in work shop B > 3) boost the main fan speed B > B > #1 appears easiest/cheapest thing to try but will it help ? B > B > #2 might be exactly what is needed but I really have no idea. B > B > #3 is beyond me. I have no manual & no idea how to check it but I've read B > that this unit has 3 selectable speeds. I'd really hate to pay a pro $100 B > or whatever to come out and flip a dip switch. If anybody has the book on B > this unit...
I would suggest going with a version of Option #2 first: might be easiest and cheapest of the three. Put a fan at the outlet (in your workshop) to pull the air from the furnace/air conditioner. The blower is currently pushing, so a little help pulling may do the trick. If you have a suitable fan you could test, else a vent-mounted fan should be obtained for around $20.
I have a bit of an airflow problem here in the Computer Room, located in the upstairs of a 1-story house. Gets a little warm in here in the summer and sometimes a little cool in the winter. Tested using a 4" muffin fan (electronics surplus) which helped but eventually died after several years. Was at the hardware store and found the 'official' vent fan: thermostat control, magnetically attaches to the vent cover, bigger blades (think it was $19.99). Seems to work even better; quieter than the muffin fan.
Note: you might want to support or suspend the vent fan. Either because the vent cover has been painted a few times or the type of metal but the magnets on the vent fan didn't hold like they should.
- barry.martinATthesafebbs.zeppole.com
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