I am replacing my 25 yo unit with another 5 ton, but am increasing the current 13 seer . The ac guy I like from talking to several is recommending a 16 seer, but most of what I read have me interested in the 18. My summer bills are crazy high. Is there any disadvantage from insisting on the 18?

You pay up front for more efficiency in exchange for lower electricity consumption. Do the math on the break even, when I did the math 8 years ago on 14/16 the 16 didn't make a lot of sense. Likely diminishing returns as you go up the efficiency scale (think 36mpg vs 40mpg in a car isn't the same as 16mpg vs 20mpg)

Agree with DrillAg 99%

1) on the other hand, guys like me that drive their cars into the ground, as well as HVACs & WindowsOS ... there have been future benefits well down the road for going to the very latest model to last 20-30 years w/o services/parts being limited or out.of.stock or freon/Puron/etc being phased out
2) local HVAC guys have always preached in-stock, lower SEERS for less money, ideal for shorter term ownerships
3) but newer models used to be better quality and now days we have to research to confirm that with little street history to monitor

If I had the option, would replace the ONE system with TWO = much better energy savings monthly, regardless of SEER, et al. Lots of client reports on file support their bragging rights.

Are both two-stage systems? If so, what is the cost difference?

Is it a heat pump? If so, Check to see if you can get a tax rebate. Otherwise try to do the math on cost savings vs up front cost. Also if the 18 is more complex, it'll be more to fix.

I just got a new two stage 15 seer and I can tell it's a lot better than my old unit.

Agree with this. Spending 130k on a new truck is fine if you are buying another one in 25 years. HVAC is the same kind of thing with a shorter lifespan. It's tough to actually calculate consumption of the two without having them both installed so the only question you need to answer is whether you are willing to spend the extra for more efficiency. You won't be able to really tell how much efficiency you're getting though other than using the energy guide info which will be iffy at best.

Lot of variables. But the house make a huge difference on what you will save. Fully variable system is cool, I have one. Doesn't make up for the 50 yo house, even with efficiency upgrades though.

Have to run the numbers, I guess. Lot depends. On the price difference.

Electricity won't be getting any cheaper

Builders used to (and maybe still do) oversize the AC systems, so you may want someone to run some calcs to see if you still really need a 5ton unit.

I know you are not in my service area but if you want to call me just to ask a few questions I will be glad to help best as I can. Jim Wolf Wise Guys Heating & Cooling 832-347-0807 is my mobile....I would concentrate more on the speed of the system than getting wrapped up in the SEER rating....meaning a single speed 16 SEER unit isn't as good as a 2 stage 15 SEER unit. AND True Variable speed offers the best climate control and overall comfort over both single and 2-speed. Single speed is for budget pricing, rentals, not planning on staying in the house for more than 4-5 years etc.

And does the 18SEER cost more to repair (ie parts) than the 16SEER?

I miss my variable speed unit. Our house was really efficient so not sure we'd ever see a payback, but man it was comfortable. Nice to just have it run at a low speed all night and maintain a steady temp vs. kicking off the covers, pulling them back on, etc.

pnut02 said:

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And does the 18SEER cost more to repair (ie parts) than the 16SEER?

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Again...its not the SEER that determines the repair COSTS. A single speed 16 SEER unit vs a 2 speed 16 SEER unit both use contactors as an example and there is no price difference....at least we don't charge you a difference. The difference comes from a 2 ton unit versus a 5 ton unit.

however, let's just say that the compressor on a single stage 16 SEER condenser unit goes bad in warranty. It is going to cost the same to repair because the labor/work to change it out is the same. If you go BUY a single stage compressor because it is out of warranty it will be slightly less expensive than the 2 stage compressor sure.... but not by enough dollars to justify the increased electrical cost and less climate comfort that you get with the single speed unit. There are just way too many scenario's out there to pin it down like that.

I will say this that I have NEVER had a customer tell me that they wish they had their old single speed unit over the new true variable speed matched systems.

My AC unit was acting up last summer. Looked to go with a 16 SEER 3.5 ton unit. I got quotes from multiple companies. Price was between $11k-14k for basic stuff up to $29k for a variable speed all the bells and whistles unit with multiple extended warranties.
I had my home warranty company fix the unit 3x instead.