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designing my OWN HVAC ductwork

8972 Views 9 Replies 5 Participants Last post by  rightit
Hi Forum, long time lurker, first time poster.

I have some ideas about a much "cooler" way to cool my home... I'm the kind of guy that thinks he can redesign all the wheels in my reach, and somehow make them rounder. ;) so if you guys would be so kind as to set me straight on a couple of ideas i've had rattling around in my head... my wife and I will appreciate it!

Right now, I have a 3 ton goodman condenser, 3.5 ton lineset (i know, weird right?), furnace in the hallway, and flex duct connecting to rigid duct connecting to more flex throughout. It's a one story 1950's ranch home, you know, the kind that has the hallway ceiling a foot lower due to the rigid rectangle above it! Also, it's a 3 sided central return, it has a return register in two rooms and one in the hallway.

So, my plan is to run a main 14" trunk of spiral pipe through the attic, strapped to the rafters, then feeding the rooms air. Also, maybe 16" spiral pipe next to it grabbing air from the ceilings of the rooms and feeding the return, replacing the ugly central return system it has now?

I hear usually it's very expensive to buy and install rigid ductwork... But at $7 a linear foot for 16" spiral pipe in 10' lengths... that really doesn't seem expensive to me... considering the entire house is so small! I know I'd have to tape and seal the joints, then also insulate the outside of the supply pipes...

So unless right off the bat I'm missing something really obvious... here are some questions that would help me get the right parts I plan to install:

1) What is the disadvantage to running a huge main trunk line the length of the house, just 40ft of 16" spiral pipe, then each room tapping into it with, say, a 10" branch VS. dropping down after each delivery of a pipe to a room, like the contractor wants to do?

2) I read it's best to suck return air from rooms from the ceilings near the inside walls... does that mean the best place to put the registers for supply air near the outside walls of the rooms, thereby making a sort of wind tunnel effect?

I can manage some serious picture overload if you guys think it would help to size up my situation? Thanks!
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Awesome, thanks! Let's say I want to go with a 3.5 or 4 ton unit in the future... Would it be OK to just get 18" rigid spiral ducting for the supplies now or would that be just too big for the current 3 ton I have now?
Marty, right, 3 tons doesn't seem to keep it cool in here. Of course, it may be that two rooms don't have ceilings or insulation... AND a lot of the windows in the house are the steel kind, single pane, very old... and the filter was very clogged up... so maybe 3 tons should be enough if the house was properly insulated.
Is all spiral pipe created equal? I'm noticing a lot of these pipe shops online are talking about dust collection systems, and only some mention HVAC... Is it that these spiral pipes are not as good for carrying cooled air?
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