HVAC Ducting - Material and Path Questions

[robs400]

Hello All - First post in the HVAC section.

Please take a look at what I am working with in my little thread I have going in a different section:

http://garagejournal.com/forum/showthread.php?t=170103&page=4

I currently have done some work to an area of my house that I would like to finish off as a work shop/garage for myself. It is currently pretty bare bones. I have had most of the electrical run and even attempted some of it myself with the help of someone that knows what they are doing.

My next big step is to move all the existing HVAC ductwork. This area was never finished off, so the ductwork was just sent straight across the room, hanging low and using lots of flex. I want to sheetrock this area now and need to move it up as much as practical, and get rid of the flex.

I had a guy stop by to give me a quote that does this for a living, and its like pulling teeth to get a quote.....I also have another buddy that said it would be fairly simple to do myself. I started looking around for duct materials...but I dont really know what I am looking for. What is up there is an insulated panel product that looks like it was cut, and folded...but I cant find that anywhere (my local ace hardware or home depot).

My question is...whats the best stuff to use? Does it need to be insulated...and lastly....how do I properly size it? I feel it is undersized right now as the one end of the house stays cooler than the other half.

A few pics to give you an idea of what I am working with...

The supply is the silver duct coming through the wall above the red trailer. The basement area is split down the center of the house...that one duct heats around 1000sq feet (with 8 ft ceilings) above my new work area.








Now dont beat up on me too bad about the flex all over the place...keep in mind I am trying to fix it! The heating system is a geothermal unit with forced hot air. The guy that knew what he was doing said he would increase the trunk line and have it hug the back wall until it hits the center lvl support beam. He would then run it along that support beam, and the branches could then be run in between the floor joists above to keep everything up high to help with the sheetrock installation.

Any info or pointers would be appreciated. Even a good website for reference. Thanks everyone.

 

[Ohmthis]

The trunk line is what we call duct board or insulated duct board. It comes in larger sheets and you vee out the insulation on the bend lines and Ben it into square or rectangle lenths. The seems are taped together. I haven't used it in twenty years. It is the cheapest way to run duct. It's restrictive, usually not done correctly and the seems will leak with age. The flex is also restrictive and a cheaper route.
I can't help you size anything without a lot of info about the air handler and room sizes. As far as routing, we don't know where the air handler is, but if it is in the corner on the back wall. Then I agree follow the wall and then turn and hug the center beam. Run the branches up in the floor joist. This is the most common routing. I would only run metal ducting and if the basement is not conditioned (no heat or air) then it has to be insulated. You can have duct built with insulation on the inside, though you could save some money and wrap it yourself. Use the insulation from the flex and put it over round metal duct and save some here too.
I won't beat anyone up over thier house, but with geo thermal that is an inefficient duct system. I would almost bet that a proper system would also solve your comfort problems too. Hope this helps!

 

[robs400]

ohmthis - Thank you for the reply....I know I dont have a lot of info at the moment, but I will work on getting some more info for you to give me some input on. I dont recall how many ton the geo unit is...but I did get that checked after I bought the house and it seems its sized correctly...just the duct work is a mess and too small on that side of the house. Thanks again, I'll be back with more info...

 

[ishiboo]

If the garage is a conditioned space, you don't have to worry too much about insulation. Flex is self-supporting, modern and is not restrictive… but it will probably take up too much space for you to get the flow you need.

Duct board you can easily do yourself, sheet metal is more of a pain. It may make sense to go with prefab plenum ducts from Home Depot/etc., and then joist panning to the rooms.

The central duct definitely looks small, as do the room vents. Find a CFM calculator, look up your furnace's CFM and venting, and get to work. It looks like you'll need one or two large plenums depending on how you'll get around the central beam. For the feeds to the rooms, you could simply branch off the plenum going "up" into the joist cavity, and use joist panning which is offered in both a metalized cardboard and the traditional galvanize steel.

 

[Ohmthis]

Get the model number off the furnace/air handler and tonnage of geo thermal. I would call around some contractors in your area and have them come out and look everything over. A good one should spend a couple to several hours doing calculations and then someone can correctly give a layout that will be best for your place. Putting in duct is not difficult, bit it can be time consuming and most don't want to be without heat or cold for very long. Take all in consideration and go from there.