Ducting Question

Old 10-11-02, 11:08 AM
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Question Two Bids on Rerouting Duct - 1200 bucks apart? Who do I believe??

I am interested in redoing some ductwork in my basement:
- I have a 3 ton furnace (old). The main duct coming out of the furnace is currently 8x18.
- The furnace, existing ductwork, and registers are all completely exposed.
- There is no need to run any ductwork behind the finished walls to the second story registers.
- I plan on replacing this furnace in 1-3 years.

I asked for two bids to date:

1 heating contractor indicated I needed to do the following:
1 - Replace the existing main duct to a 10x18 (custom duct) b/c the 8/18 was restricting the airflow below the 3 ton output of the furnace. He indicated that leaving this 8x18 duct in place would be problematic when I wanted to upgrade to a newer furnace and the duct would have to be replaced at that time to avoid burning out the heat exchange on the new furnace.

2 - This new 10x18 duct would be extended to the other side of a specific beam where I wanted all the registers be tied into it.
Essentially he would be extending the duct on a straight line about 15 inches and ripping out some existing ductwork that is sitting under a stair landing I want to lower and replace.

3 - The main run would be turned left on the otherside of the beam and all 7 heat registers would be tied into it at that point. 3 of these heat runs are new runs I am adding to the basement, the other 4 are existing registers, all of which sit right over where the new main duct is being routed.

4 - A second air intake would be added in the finished basement room - about a 4 foot straight run with no access issues.

5 - He will seal all ducts with duct sealant and all 7 heat registers would be equipped with manual dampers.

Final price - 2800 bucks.

The second heating contractor just bid on rerouting the existing main duct (no size change) with the same amount of new runs and no additional air intake. His price was $600.

Was the more expensive contractor just being more proactive in telling me the "right way" to do this or is he upselling me?

Please help!
Old 10-11-02, 01:11 PM
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Lightbulb Install TWO systems

For the price of redoing the ductwork you might want to consider going with TWO separte system for up and down.
Comfort would be greatly improved.
WThis would reduce the problem of hotter upstairs all the time.
Old 10-11-02, 02:15 PM
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2 systems are good, but you also multiply your maintenance and equipment by 2.

I had a dual system in previous house, and it was an OK performer. The AC for the 2nd story ran constantly and the electric bills were very high. But, we were comfortable upstairs. I thought I would save $ when we did this, but that was not the case.

We moved into another 2 story house with a single system. We replaced the 20 year system with a new system with a variable speed blower. The fan runs constantly (at low speed) and circulates the air thru out the house that virtually eliminates hot spots and the 2nd story is very comfortable on the hottest days.

The AC is very efficient (16 seer) and electric bills are lower than previous dual system house.

Now, the VS blower was a little more expensive, but well worthe the addes $.
Old 10-11-02, 10:10 PM
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But what about the cost?

Thanks for the suggestion on 2 systems. The problem remains that I do need to reroute the existing ductwork to accomodate my new stairway route.

Given my original description, does 2700 sound like a lot or was that contractor specing the job correctly?

Thanks so much!
Old 10-12-02, 07:43 AM
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Question Stairway route

Just install the 2nd system in the attic, then you you won't need to re route the ductwork ??
Old 10-12-02, 12:46 PM
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Duct work

That 8x18 duct you have is not big enought for 3 ton no way.
Thats 48" per ton any good book will say, you need 60"to 80" per ton for a good job. That 10x18 would be just at the 60" per ton and down the line with a new unit and a VS blower i think it would work out for you up and down.Cost less to have just one unit stoping and starting ED

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