HVAC System Replacement - Tons vs SEER Rating - DIY Advice?

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Old 05-05-18, 10:57 PM
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HVAC System Replacement - Tons vs SEER Rating - DIY Advice?

Hi Guys,

Considering replacing some of our AC units. Was checking out the prices of the 4 Ton units vs 5 ton units, and saw they were virtually identical. In other words - the 18.3 SEER 4-ton Goodman system was the same price as the 16 SEER 5-ton Goodman system.

Which system would have a lower cost of ownership? A larger tonnage and lower seer, or higher seer and lower tonnage?

I know this is much more involved than watching a few youtube videos, so wanted to make sure my idea was practical before trying to tackle replacing the units one at a time.

House Specs:
  • 3 Story - 4100 sqft
    • First Floor: 1500 sqft
    • Second Floor: 1800 sqft
    • Third Floor: 800sqft

Current System
  • Age: About 20 Years Old
  • Make: Trane
  • Model: XL1000
  • Number of Units: 3
  • Unit Sizes: 1.5 Ton, 2 Ton, 1 Ton

Fuel Types
  • A/C: 240v Electric
  • Heating: Propane

Goals
  • Reduce our electric bill - our worst months can be $500+
  • Reduce our propane bill - since we installed our wood insert, our heating costs have come way down. Originally, our worst bills were $600+, now they're closer to $200+ in winter
  • Humidity Removal: I can't stand feeling sticky. We're in Charlotte, NC, so the summers here (Jun - Sep) can easily average >90 degrees with high humidity.

The main reason I'm considering doing the install myself is the costs contractors want to charge - they seem totally ridiculous. I want to say 2 years ago, we were looking at a 3 Ton - 14 Seer Goodman system installed - and it was around $10k, and that was just for 1 of our 3 units. Naturally, I checked out ACwholesalers...and found the complete system was less than $2k. After checking around, some contractors were (surprisingly) higher, and a few were lower, but I still couldn't wrap my mind around why having a crew install the system, which I was told would be done in a day, would cost me $6-8k. So, I figured I could maybe start with the 3rd floor system since it's the easiest to access and the smallest, and maybe try to install a new system myself. Meanwhile, the other 2 units could keep the house semi-comfortable. Thanks for any advice.
 
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Old 05-06-18, 03:00 AM
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A larger tonnage system should never be considered an upgrade of any kind. You should start with a heat load calculation to see what size you actually need.
If your current units are between 1 to 2 tons, a 5 ton is ridiculous.
 
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Old 05-06-18, 06:54 AM
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Bigger system = cools faster = less run time = less humidity removal = lower temp needed for comfort = longer run times = higher costs. See how there is a conflict with a bigger system.

To help with hiding the problem with over sizing you can get a two stage or even variable stage system.

Heat load calculation / Manual J - HVAC Load Calculation - Maunualj - Whole House Loadcalc

You need the EPA certifications and tools to do it yourself. First is removing the old system and recovering the refrigerant - then working with a recycler.
 
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Old 05-06-18, 07:53 AM
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DIY is possible, but much time is needed to do the research and learning. Not practical for most people. DIY will also void the warranty, consumers reposts says that new coils have a 10% failure rate.

First thing to do is the heat load calculation shown above or hire someone to do it. Then read about sizing duct work, called a manual D, this is where most systems are messed up.

Get more estimates, going through life I usually got 2 or 3 estimates for anything and sometimes just hired the people that were recommended without getting estimates. This time I got 11 estimates, 9 of which had no idea what they were talking about! 2 estimates from knowledgeable people one of which was real high, likely did not want the job. 1 estimate in the ball park. Estimates were $4k to $8k, some of which I referred to as drive by estimates or as pro's call them smash and grabs. Best price and knowledgeable contractor was $5700.

I liken high SEER ratings to more problems and higher repair costs. All of this is of course only my opinion and worth what you are paying for it.
 
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Old 05-06-18, 03:42 PM
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Whole system install is not a DIY job. Try to shop around and ask as many questions as you can. Current estimates are some where between $5000 and $10000 depends on where you are. Consider one system with 3 zones which may save you some money.
 
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Old 05-12-18, 04:55 PM
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Originally Posted by Astuff View Post
Bigger system = cools faster = less run time = less humidity removal = lower temp needed for comfort = longer run times = higher costs. See how there is a conflict with a bigger system.

To help with hiding the problem with over sizing you can get a two stage or even variable stage system.

Heat load calculation / Manual J - HVAC Load Calculation - Maunualj - Whole House Loadcalc

You need the EPA certifications and tools to do it yourself. First is removing the old system and recovering the refrigerant - then working with a recycler.
Thanks Astuff...that's about as clear and concise of an explanation as I've heard with regards to larger AC systems.
 
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Old 05-14-18, 01:31 PM
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I'm not sure how the 5 ton came into play if you have a 1.5 Ton, 2 Ton, 1 Ton.
 
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Old 05-15-18, 08:40 PM
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If you DIY this, you should leave the refrigeration (brazing, evacuation, charging), gas and venting work to a pro.


You mentioned high propane bills.

It may be in your interest to look into heatpumps instead of a/c units. They use electricity, but when electricity and propane are price similarly (as they often are) or better yet electricity is cheaper than propane, the 200 to 300% efficient heatpump saves money.

You keep the propane heat for when it gets too cold for the heatpumps to keep up. (you start using the wood insert at this point to reduce propane use) A dual fuel thermostat with outdoor sensor is used to control the system.

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Edit: I just looked at your climate data, winter highs average well above freezing it seems so with heatpumps you would barely have to burn any propane.

What's your all inclusive electric rate?
Propane rate?
--------------

As far as high efficiency equipment goes, certainly today's equipment will reduce the bills. But, it's more important to have a well insulated house, good duct system, proper airflow, etc.

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You can't just upsize a unit without re-doing all the air ducts to handle the higher airflow required.

You'll be better off staying in the 1.5 to 2 ton range for each unit. three 4 or 5 ton units is crazy, there are energy efficient homes out that your size that cool with one larger unit.

This isn't like buying a television where bigger is better and you just take it home and plug it in.

These systems are engineered, have to be tuned on site. The machine is just like an engine for a custom car, and it needs to be a good match for every other part.
 
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