Attic vs roof mounted AC:


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Old 03-08-11, 10:49 AM
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Attic vs roof mounted AC:

Attic vs roof mounted AC:

We have an 1,800 sq ft, ranch style house, with block (CMU) outer wall construction (on a slab), and no basement, that was built in 1966, in Phoenix, AZ. One original main trunk-line duct for the original gas furnace and the original evaporative cooler runs the length of the house. The evaporative cooling unit on the roof was soon replaced by a centrally mounted (just below the ridge away from the street) self-contained roof type AC unit which died in 1983. The current TempStar 4 ton AC/gas furnace installation is in a hall closet that formerly contained the gas furnace (and a gas water heater, moved to the laundry room to facilitate the 1990 AC/furnace installation). The compressor had to be replaced in 1997 because high pressure start-ups (indicated by very loud start-up noise that we were mostly ignorant of due to block wall suppression of the noise) wore out its valve system. The technician who replaced the compressor had to spend 5 to 6 hours trying to eliminate that high start-up noise in the new compressor. (I assume in hindsight that he was gradually reducing the refrigerant charge from the factory specification.) During the hottest part of a Phoenix summer the current unit runs a very long time.

The current AC/furnace uses the original "furnace only" right angle, side entry sheet metal duct for the supply air connection to the main trunk-line duct. Rerouting (or expansion) of supply air connection for top entry into the main trunk is constrained by a ceiling joist, and the size of the closet limits any shifting of the position of the evaporator/furnace unit. The main return air register (nominal 12" X 38", actual 10" by 36") to the plenum below the closet door is very noisy just in terms of air flow noise through the vanes. Expansion of the main return air through the plenum register is constrained by the surrounding bathrooms and hall cabinetry.

(There is a 2nd air return that uses the old hallway ceiling register leftover from the old rooftop AC unit. It is connected by a long flex duct that arcs up and then down through the closet to enter the top of the plenum at the back of the closet. A single sheet of paper will stick to the ceiling register grille when AC is running. But it has not diminished the main return air register noise.)

We have both a return air restriction causing noise and a supply air restriction limiting efficiency. I won't shock you by stating the number of AC contractors who looked at this system and gave us estimates for a Trane AC system replacement before one of them noticed the supply air restriction problem. After a few more contractors came out one contractor estimator got out his official Trane duct sizing, airflow capacity cardboard wheel calculator, a tape measure, and a device for measuring 'static air pressure'. In short order he declared that we would never be happy with any new system if it was installed in the hall closet. "If I fix the supply air restriction, the return air noise will get even worse. And solving the return air problem would require moving the closet and/or invading the cabinetry. If you want an AC installed in this closet, we won't do it."

So many contractors were willing to give us whatever they thought would quickly satisfy our desire for a new AC unit, even though we stated emphatically that we wanted the return air noise problem solved. They confidently reassured us that a Trane new system installation would solve all noise problems (with various expedients such as a baffle and acoustical insulation in the plenum to force the 2nd air return to pull more air into the hall ceiling register) and operate at the new Trane unit's rated efficiency. Even after I alerted them to the airflow restriction problem inherent in the current closet design they continued to adjust the closet design. They seemed to be following the sales path of least resistance. Part of this is my fault as I recounted our continuing problems with the roof leaks and sheathing deterioration left over from the old roof-top mounted AC unit.

(Just last summer we finally had the old rotted sheathing replaced with radiant barrier, code thickness sheathing, and also had new 30 year 'Certainteed' asphalt, architectural shingles installed on top. We also intend to have a 2" foam EFIS stucco insulation system applied to the outside of the block wall within the next 2 weeks, which should drop the heat load calculation considerably. And we intend to upgrade the attic insulation from R-11 to R-30 after the AC system is installed. All glass windows and sliding doors are dual pane, fiber-glass frame.)

I am very loath to have someone cut a big hole in our new roof. So I asked the more impressive contractor estimators to give us estimates for both a roof-top mounted and a split system with the evaporator/furnace hung in the attic. The one contractor that seems to know the most about what he is doing (he was the only NATE certified estimator in the bunch) tells us that it will cost $2,800 more to put a split system in the attic as compared to a single unit roof mounted model (which is approximately $10,000 including tax, give or take rebates for a Trane XL16c 4 ton, 16 SEER, two stage compressor). That would make his attic system price $12,800. Obviously the NATE certified estimator wants nothing to do with an attic split AC/furnace installation. (These are all "Trane Comfort Specialists" that we have estimates from.)

Attics are nasty but its still March. (Maybe we could get by until October.) Both installation designs require rerouting of electrical and gas connections, and a crane to help install the unit (the attic split would enter through one of the gables). The roof mount requires cutting that big hole, an angle iron stand, a special sheet-metal 'elbow' 2-way duct connection, and special care to see that roof penetration does not develop leaks. The attic design requires new refrigerant line connections, walking around slightly bent over while doing the installation, special hangers for connection of the unit to the rafters (maybe even vibration dampers). Trane roof-top single unit ('self-contained') models appear to be rated as less efficient than comparable Trane split system models. The attic temperature may impose more heat load than a roof-mount system (even with the radiant barrier sheathing).

Should I ask the NATE certified estimator for an itemization of the extra costs of an attic split system? Or would that just waste time as he would most likely invent expenses to prevent us from choosing a split system attic installation? (The NATE dealer "standard warranty" is compressor 10 years, parts 5 years, and 2 years labor. An extra $590 gets you an "upgrade" to a factory 10 year warranty on parts and labor.) Should I just go with another contractor that seems to be more at ease with installing an attic split system for not much more cost than installing the roof mounted package? (A second contractor's attic split system package will cost about $11,000 including tax, not counting rebates. The factory warranties are 10 years for parts and labor, and 12 years for the compressor. The dealer warranties are 10 years on all installed parts and labor. I don't understand why the "factory warranties" for the same brand and same model # AC unit should vary at all from dealer to dealer. This other contractor did not submit a roof installation estimate.) Or would that just lead to an unsatisfactory installation and future problems because all of these other contractors are still just taking the path of least sales resistance, or worse they really don't know what they are doing? Is an attic installation fatally flawed engineering-wise compared to a relatively simple roof-mount installation?
 
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Old 03-08-11, 01:18 PM
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I can tell you this, you get what you pay for, take that for what it is worth. Installation done correctly is going to net you a more comfortable home and increased longevity of the the HVAC system.

Warranties on the same unit........Factory is 5 year parts on trane...PERIOD..... If one contractor offers you longer warranty on the same equipment then it is simply the contractors warranty or they are including the extended warranty in their price and not giving you the option of the lesser warranty.
 
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Old 03-08-11, 07:27 PM
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I have further figured out that the factory warranties whatever their length do not cover the labor or other costs to replace the worn-out or defective part. And the dealer/installer warranties only cover labor for the non-factory parts. But the "extended" warranty that the factory offers (the only way to get a factory labor warranty) costs about 2/3ds the labor cost to replace the compressor, probably the most expensive part to replace.

Extended warranties are inherently inefficient because not everybody antes up. The admin costs of keeping track of who has an extended warranty increase the costs that must be covered by all of the customers that purchase the extended warranty.

Plus the company knows it can add on some more profit as some people always purchase the more expensive options. It's not quite like the classic "tapping the demand curve" from economics class, but it comes pretty close. If everybody who purchased a product received the same warranty for the same one inclusive price the company would have more incentive to reduce the cost of that warranty, because it affects the competitive price of their entire, main product line.

An 'extended warranty' is a side item like French fries, or the super-duper sports car trim package. Once you've decided to purchase a McDonald's hamburger, or a Ford Mustang, or a Trane air conditioner, then any other options that you want, you will have to purchase from McDonalds, or the Ford dealer, or the Trane dealer. So monopolistic pricing is a factor in extended and/or expanded warranties. Once you've decided on the brand of product that you want you are locked in to purchasing the extended warranty from the same company (certain credit card programs notwithstanding).

All in all purchasing an extended warranty just don't seem warranted to me. But I might be convinced by some hard practical, 'specific case' facts that I am not yet aware of.

I am now leaning even more strongly toward the attic split installation configuration. But I might expand the brand name limits to more than just a Trane air conditioner. Supposedly the comparable Lennox model has smaller dimensions and might be easier to install in the attic. Well it's off to the Lennox website. I've got to decide this question in the next week. Otherwise it will be to hot in the attic to install anything correctly. Thanks
 
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Old 03-08-11, 07:49 PM
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Beware, Not to deter you from Lennox as I used to work for a Lennox dealer. They are more a monopoly in my area than any other brand. This may not be true in your area, do your research. Lennox parts tend to be less universalistic, if that is a word. What I mean by this is that Universal parts for lennox equipment is harder to come by and Lennox parts are harder to come by in my area. There is no Lennox parts wholesaler or parts warehouse in this area. There is only a HVAC company with a local name who is owned by another company who is owned by Lennox. Therefore, that company has a monopoly in this area for Lennox parts. I can get these parts, but it will take longer to do so, and I also purchase them at a higher price. This brings the point up that a consumer would be better off using that HVAC company because the repair could potentially be done sooner and at a lower cost to the consumer.

I bring all this up just as a notion for you to do some homework on availability of parts and prices. Also to do some homework on the servicing and installing company to be sure you are happy with them and that you have options available for other companies to provide you service should you become dissatisfied with installing company.
 
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Old 03-09-11, 03:25 PM
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Thanks for the heads up. I ran into that problem in another context. I unfortunately bought a Westinghouse 47" LCD TV and after 2.5 years I can't even get the parts to have it repaired. The phrase "Westinghouse Parts" is an oxymoron, a contradiction in terms. And Westinghouse couldn't care less.

With regard to the AC install I have been told that currently most new home construction in the Phoenix area involves in the attic AC installations. Obviously an attic AC installation is a much easier operation during the construction of the house. But it does indicate that there are contractors in Phx that know how to do attic AC installations and have a lot of experience with doing them. I am now asking the competing contractors for the names of reference customers who have had an attic AC installation, and also the stats on how many attic AC installs the contractor has done in the past year. I think that references and install stats should indicate the best contractor to go with. Currently I have 2 estimates for an attic installation that are only about $1,000 more than a roof-top installation. The second Lennox estimate for a system comparable to the Trane was about $2,000 more than the Trane estimate from the same contractor due to the higher Lennox product price.

I have also been told that the reason that the majority of homes in the Phx area still have roof-top mounted AC units is that we don't have basements in Phx. And just like my current post-construction, hall closet, split AC installation, hall closet systems, whether during construction or post-construction, have more come-back problems than roof-top installations and their initial installation is more expensive.

Again, thanks for the heads up about Lennox parts availability.
 
 

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