What do you know about ductwork??

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Need help here...scenario, old house that needs floor jacks. Ideally, I'd like to stretch an I-beam or 6x6's across basement ceiling, but old, round heating pipes are in the way all over. Ductwork is filthy and largely inadequate, & I'd like to take it all out, but to replace with new metal that would fit between the floor joists would cost a FORTUNE! The blown-up oil burner will have to come out, but wood-burning furnace next to it will stay.

Are there any alternatives to buying sheet metal ductwork? Would sure like to know of a source for aluminum-wrapped, pressed fiberglass in a rectangular shape that would fit between the floor joists, as in a mobile home. Or, someone said that some new homes are being built with metal sealed on the bottom of the floor joists, using the joists as the carrier for heat until it goes up the walls or registers. Is this true? Would it dry the wood out too much? Anyone got any ideas??? Sure would appreciate any and all comments... Thanks!!

-- Bonnie (chilton@stateline-isp.com), August 16, 2001


First figure out what you have, Is it a heating duct or a cold air return? The metal on the joist and use the wall as a cavity is true, even on new houses but that is ONLY for return air. Heated or cooled air must be contained inside some duckwork, meta, plastic etc. Do you still have an old furnace or a new modern unit. You may be able to shrink down the size of return air vents and ducks

-- Gary (gws@redbird.net), August 16, 2001.

Thanks, Gary. Someone told me if I lined the floor inbetween the joists (and the joists) with aluminum, I could use it as a hot air channel also. What do you think?

-- Bonnie (chilton@stateline-isp.com), August 16, 2001.

Bonnie there is a system called mini ducts, it is for retrofitting older homes that have never had A/C or Heating, like historical homes, I have been checking them out for my dome home because there are no ceiling for ductwork.

-- Deborah (theant00@yahoo.com), August 16, 2001.

I tend to know a ittle bit about this subject,worked in A/c trade for 25 years,even owned my own company. You can go to any lumber supply house,buy 4X8 sheets of foil backed duct board,and use it to manufacture any size or shap ducts you need.Cut it with a razor knife,duct tape and staple it to seal it.You can cut it to fit over the floor joists and use that for either supply or return air ducts. Where it first starts out from heat source,put peices on top and sides,as well as bottom of course,for about 8 feet.This keeps the wood from getting o hot right at that point. Also,you can buy and use Flexible duct.This is duct made of plastic,wrapped with spring steel wire,then covered with insulation,then covered with a plastic covering.This comes in all sizes from 4" up to 24" and it comes in 25 foot lengths.Comes in a box about 3 feet tall ! Highly compressed in box. You can use this anywhere you can use metal duct,and a lot of places you cant... Both of these system are code compliant,perfectly safe to use,and will last many years. Hope this helps. Also,where you run flexible duct,you can sort of flatten it to get around or under joists. Good luck. Don

-- Don Sloan (twosloans@texxoma.net), August 16, 2001.

I agree with Sloan, the fiberous and flex duct combination is the only way to go. I also had my own a/c business for 20 years and taught a/c at a community college for 5 years. The only thing I would add are two very important points:

First make sure you size correctly, especially your return ducting. Undersizing is the most prevelent mistake I have observed in the market today and it is a rampant problems. Because 6" duct is cheaper than 8" duct, etc. it always gets squeezed down till it's just not big enough. you'll probabably have to seek some professional advice on this subject and the Trane A/C company makes a sizing device called a ductulator that is absolutely indispensible.

Second. You need to be sure that your ductwork is PERFECTLY sealed. Liberal quantities of a product called mastic with mesh cloth is essential on all joints and seams. This is another area that most contractors shortcut and it can have a profound effect on your system performance as well as indoor air quality. Just 10% leakage can cause major problems and reduce your systems capacity significantly. The contractors usually compensate for this by oversizing your system which can lead to a host of other problems and is very inefficient. Doing it yourself is not out of the question but it's a big undertaking if you haven't had any training. My advice is try and find someone with experience to coach you along. If you have a trade school in your area that's often a good source and we routinely used to help homeowners with problems where I taught. Usually fixing contractor screw ups. Good luck with this one.


-- Carter (chucky@usit.net), August 16, 2001.

Your local Lowes or Home Depot should have books availab;e on the latest techniques,many of which are not that quite expensive.

-- Jay Blair in N. AL (jayblair@yahoo.com), August 16, 2001.

What would be wrong with using thin-wall pvc? Its cheap, very easy to use, easy to clean (inside) if needed, and sure won't leak.

-- charles (clb@dixienet.com), August 16, 2001.

Two problems with pvc. First, to install it with the required cross sectional areas for proper duct sizing would be cost prohibitive and secondly, it's not a good ideal to have pvc anywhere around your air distribution system. In the event of fire it gives off deadly poisonous gasses and the smoke from burning PVC is probably responsible for more deaths than any other burning building material. Some municipalities have even banned it for installation above grade which I personnally think is rediculous and paranoid and only adds unnecessary cost to construction but thats what building departments and code requirements usually do.

-- Carter (chucky@usit.net), August 17, 2001.

What great suggestions! You've all given me hope, and I thank you so much!

-- Bonnie (chilton@stateline-isp.com), August 17, 2001.

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