Central Air Prices

[mysticokra]

We are doing extensive remodeling, so I got bids on a zoned Central air system.

3 Seer 13 Heat Pumps were recommended from vendors ranging from Lennox to Trane.

The prices ranged from 13 thousand to 34 thousand.
How can there be that much variance?
Are they playing "how stupid are you" with me because we live in rural setting?

The house is two stories and about 4,000 square feet.
2,800 of that would qualify as new construction, so installation should be a breeze. (Pardon the pun) [img]/forums/images/icons/grin.gif[/img]

[Pat]

mysticokra, 13 SEER??????????????? WHOA there, not enough. Unless your electricity is free or nearly so and guaranteed to stay that way for the next couple decades, you need to be considering a higher SEER unit.

Be advised that the majority of HVAC sales and service outfits have no engineers on staff and typically sell too large a unit for two reasons: !. they don't really know how to figure the right size so they over do it to make sure it cools, and 2. the bigger units make them more profit.

I have a couple 19.2 SEER Lenox units that have subsequently been improved and are now being sold as 22 SEER units. Do the math. Check the cost of the equipment, installation, estimated maint for the liife of the unit (20 yrs), and the cost of running it for 20 years. If you don't have a crystal ball use todays energy costs knowing it will most likely get more expensive over time.

When you add up the lifecycle cost of the various candidate systems you will get a realistic comparison between units. The standard system for my mom's house was electric resistance heating and A/C. Cheaper to buy but hellishly expensive to operate. I got quotes for a heat pump and an upgrade to a high SEER heat pump. I did the math and estimated a breakeven on the cost of the high efficiency unit as about 3 years and after that the savings would be money in the bank, literally.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[Nat]

To add to what Pat said if your AC unit is bigger than what is needed it will run less often an therefore will dehumidify less. If you need AC then you need it to remove as much humidity as possible and a larger than needed unit wil cycle off to soon and not do the job of dehumidifing that is so critical in being comfortable. And as he said most will try to sell you a bigger than needed unit. A smaller more effeicent uniyt will keep you much more comfy. Later, Nat

[Pat]

Oh, and there is another consideration too besides adequate dehumidification making you comfortable at higher temps so the delta T is lowered giving lower op costs.

There is an efficiency curve on the compressor based systems. Efficiency at startup is low and increases during a run approaching the best it is going to do within say 45 min or so. An oversized unit knocks the temp down fast so it doesn't circulate much air which is why it dehumidifies so poorly. BUT the short run is at poor efficiency with the unit shutting off before getting to better efficiencies. Then several minutes pass and it comes on again at its lowest efficiency and runs briefly and shuts down before getting up very far on the efficiency curve. (lather rinse repeat)

So, you pay more to run it because you are never getting to the "advertised" SEER and you pay more because you have to use a lower setpoint to feel comfortable because of the high humidity. The lower setpoint means a greater differential between inside and outside temps which drives more Btu through your insulation.

A "rightsized" installation is more difficult to engineer so folks lacking in ability just oversize the unit, take the extra profit, and don't get callbacks from you because it does cool doesn't it? But at significantly more expense in the utility bill and all the short cycling will wear the unit out earlier (maybe past warranty) which is good for the service side of the company that installed it. Job security.

There are units on the market that have variable speed compressors and units with multiple compressors. These run at a low speed a lot of the time in hot humid weather and dehumidify fine. If they cant keep up they speed up for a while untill they catch up and then go bacl to low speed. The two compressor units run one (usually the smaller) unless it won't keep up so it is also running efficiently and dehumidifying. Either is a good way to go, 2 compressor models or multi speed compressor. Copeland scroll type compressors are the way to go now.

You will find the initial cost is likely higher to "do it right" but total cost over the life of the equipment will be significantly less with the right installation. Also be sure you either have metal duct or high quality flex duct, not the old style. Ensure that all ducts are sealed well. The majoprity of HVAC ducts in use today are leaky and average over 15% leakage (hemoraging $ into the attic.) You can pay now or pay more later in monthy installments to the util company.

If you can, run the ducts in conditioned spaces rather than the attic. This makes a significant difference. For example you can have a multi level ceiling in some rooms with a sofit around the perimeter. the ducts can be run in those. You don't need to insulate the ducts when they are run in conditioned spaces. make sure that all joints are sealed with "duct butter" or equivalent elastomeric joint sealing compound. Do not, I say again, DO NOT use duct tape on ducts. It is good for many things but sealing ducts isn't one of them. It will "let go" and leak like hell in short order. Only use adhdhesive backed foil tape or better.

I know I sound like I am indicting the HVAC industry as a bunch of marginally skilled pirates who mostly do oversized poorly engineered installations. You can verify this opinion by reading in the Government DOE sites and the trade mags. Want to stump a chump? Ask your HVAC guy if he will do a blower door test and see if he has a clue what it is. He may have heard the term but it is a small minority who actually do things like that. You mean you want witness a duct leakage test? We dont test the ducts. We been doing this for 30 years and never done one yet! Typical attitude. Bragging on how long they have been doing it wrong and never trying to modernize or learn anything new.

There is more to getting a good HVAC job than getting 3 bids and picking the cheapest.

[img]/forums/images/icons/smile.gif[/img] [img]/forums/images/icons/smile.gif[/img] [img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img] [img]/forums/images/icons/smile.gif[/img] [img]/forums/images/icons/smile.gif[/img]