Heat Pump Ductwork/Trane XR14

16 years ago

I have received estimates from 5 HVAC companies. The contractor that I liked the most came in with a quote significantly higher than most of the others--however, he seemed more thorough. Background: We have plaster ceilings and need all ductwork put in in the attic. It's a one-floor ranch. About 12 supplies and 2 returns.

The proposal is for either a Trane XR14 or XL14i heat pump (with a Trane variable speed air handler). The contractor will build a plate from in attic to install aux-drain pan with air handler over a drain pan. Duct made of metal trunk duct with exterior wrap insulation and flex drops. Duct seams sealed with mastic for maximum efficiency.

Questions:

(1) Is the XL14i really preferable over the XR14? It is more expensive.

(2) Are metal trunk ducts necessary? Are they much more preferable than rigid fiberglass?

(3) Is it important to have the ducts sealed with mastic?

(4) A competing proposal includes a "spider" set up. The proposal we are considering is for ductwork that limits the length of the flexible branch ducts.

The proposal comes in around $14,000+. According to the contractor, the items above push the cost up (especially (2), (3) and (4)).

Comments please. Your help is appreciated.

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Comments (2)

garyg
16 years ago
I am only a home-owner, not an HVAC pro, but here are my 2 cents:

1. Post the model numbers of both the condenser (outside unit) and air handler. Example: Condenser is 2TXW..., air handler is 2TEE... With model numbers of both units, the output (BTUs) and system performance (SEER, EER, HSPF) can be determined. I think the XL14i may be being phased out (that's not a bad thing, but you should ask the contractor)

2. I have all-metal ducts in my 1986 home. They are a little noisy. The diameters can be made smaller because of less air flow resistance. I think that metal is preferred but I'm not sure.

3. Yes. Since your ducts are in the attic (hot in summer, cold in winter), they must be sealed properly to prevent loss of supply air or pickup/loss of heat in return lines.

4. Not sure but I would want to minimize spidering. Your new Trane system is only as good as the installation and ductwork. Bad ductwork = bad air flow = bad system.

I would guesstimate that more than half of that $14k is for ductwork and labor associated with the ductwork.

Can you get more than 2 returns? The returns are very important for proper air flow.

I would also get a 10 year PARTS AND LABOR warranty for your piece of mind.

Best to you.
thull
16 years ago
Also just an owner/DIYer, although I have a day job as an engineer.

Garyg has it right on rigid duct being preferable to flex. If you can, you want to limit flex duct runs to the 5 feet or so at the end of each run. I don't have any experience with rigid fiberglass duct. I'd also go for several more returns to get full coverage.

Since you're investing in a new system, you want that system sized properly. The gold standard for sizing is ACCA Manual J for the cooling equipment and Manual D for ductwork. I'd be concerned about anyone who was just going on square footage to determine AC tonnage.

The other thing I'd want done is a duct blaster test on the installed system. Basically this determines how leaky the ductwork is. If the contractor has the capability to DIY the test, that'd be a great sign.

If not, there are 3rd party testers who'll do it for a couple hundred bucks. But, and this is a big one, if the contractor hasn't had his ducts blown before, I'd have him talk to the tester before starting to understand what kind of extra steps he may need to take that he isn't accustomed to. A good leakage rate for a newly-installed duct system is 0.05 cfm/sq ft- that's cubic feet per minute per square foot of your conditioned space.

My perspective is that we used a contractor (existing house, new system in attic) who said, "yeah, I put in tightly sealed duct." It tested at over 1-ton of leakage on a 3.5-ton system. Even though I thought we'd made it clear up front what we expected (and that he had the opportunity to adjust pricing accordingly), it turned into a big mess. And I inherited the job of going back and finding the leaks and patching them.

If I had it to do over, I'd still want the system sized properly and installed with minimal leakage. And I'd have hired someone else.

Here are some resources:

http://www.southface.org/web/resources&services/publications/factsheets/22blowdoor.pdf

http://www.southface.org/web/resources&services/publications/factsheets/2duct_q&a.pdf

http://www.southface.org/web/resources&services/publications/technical_bulletins/HCES-HVAC-selection%2002-779.pdf

http://www.southface.org/web/resources&services/publications/technical_bulletins/DD-Air-sys-design%2002-0782.pdf

http://www.southface.org/web/resources&services/publications/technical_bulletins/DIS-Air-sys-install%2003-0783.pdf
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Heat Pump Ductwork/Trane XR14

Comments (2)

garyg

thull

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