Another AC Decision

Personal Finances Building / Maintaining a Home
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I don’t know that I have a specific question, but comments and thoughts are solicited.

My house here in Connecticut was built in 1989; 2144 sq ft ranch. I bought it in 2000. This is my first time having central air. It has worked fine. The 4 ton compressor out back was made in 1989, so it is original - and over 40 years old. The air handler (fan coil) in the attic was replaced in 2016 when the house received a major overhaul. The AC is all one zone, with eight ceiling vents around the house, air return and thermostat in the central hallway.

40-plus years is pretty old for a compressor, and I’d rather not be reacting to a failure during peak cooling season. I’ve had one HVAC outfit in, checking it out and giving me a quote on upgrades.

I had hoped to just replace the 1989 compressor. Nope. It uses the old - banned - refrigerant, and as a result the air handler (fan coil) and tubes that run between the two are lubricated with stuff incompatible with the proper refrigerant. All that can be salvaged are the ducts, the concrete pad, and the power connection. The refrigerant tubing, currently in the wall, will be replaced with exterior tubing into the soffit, with some sort of cover for the vertical stretch.

I’ve got a quote from a local Carrier dealer. Three quotes from them, actually. The base model proposal is $12k for a 13 SEER single stage. The middle choice is $15.8k for a 16 SEER single stage. The top of the line choice is 19 SEER variable speed for $18.4k. That one has variable speed for both the compressor and fans.

Complicating the choice is that I am getting close (at least I think so) to going solar, with the south facing roof carrying 12.8 kW of Solar Panels, with 2 Powerwalls in the basement. That was configured to handle the old AC, at least in theory. The starting surge of the AC is the critical point for running off the Powerwalls. Between the sun and the Powerwalls I should be able to last through a few days of the power being out.

Anyway, the “savings” from higher efficiency AC is offset by the fact that my electricity is going to be really cheap. Just as the “savings” from going solar are based on my old usage pattern. But I really didn’t decide to go solar based on saving money, it just seems like an obvious thing to do. (The first time I saw the house, with that unshaded, south-facing roof, I knew it deserved solar.) And I’m not usually one to cheap out; what does motivate me is reliability.

Thanks for any thoughts.

1 Like
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Do you have forced air furnace? Are they replacing furnace too.

Part or the deal for highest SEER is replacing ac fan motor with electronically controlled variable speed motor. That usually requires replacing furnace too. They usually require a service contract to keep it running.

I’d go with the 16 SEER unit. More reliable. Less finicky. Not as service dependent.

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Just saw an analysis saying Heat Pumps will cost less than a gas/oil furnace and an AC unit for total energy cost - and this was with oil prices as they were a year or two ago. Yes heat pumps can’t compete when it is below say 10 or 15F outside - so HP systems us resistance heating to supplement the heat pump on those few days per year with really code weather.

I want to say MA recently pass a rule prohibiting fossil full during heating units in new construction - but maybe it was Boston.

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Would you be going 100% solar or would you still have a connection to your local power company? If you are still connected, you’d have power for your AC unless there was a power outage. In that case you could turn off the AC until power was restored, or just run it for part of the time.

Leana

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Would you be going 100% solar or would you still have a connection to your local power company? If you are still connected, you’d have power for your AC unless there was a power outage. In that case you could turn off the AC until power was restored, or just run it for part of the time. – Leana

One possible solution would be to have a whole house backup generator in case the solar meets a situation that it can’t handle. Assuming the solar has some sort of energy storage to handle stuff like nightfall.

Rob
Former RB and BL Home Fool, Supernova Portfolio Contributor & Maintenance Fool
He is no fool who gives what he cannot keep to gain what he cannot lose.

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Do you have forced air furnace? Are they replacing furnace too.

No. Heat is oil-fired hot water baseboard, two zones.

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The two Powerwalls provide a backup when the utility power is out. The solar panels can charge them during the day. I would have to adjust usage to stretch it out, but I should be able to keep the essentials (oil fired boiler and circulators for heat, power to refrigerator and freezers, also probably internet and computers) running for a good while in the winter and perhaps indefinitely in the summer.

The house will still be connected to the grid. In theory excess that doesn’t go into the Powerwalls will go to the grid and make me some money back. In fact there is an agreement that when the grid needs power of a summer evening it can draw on my powerwalls, for which I get paid.