We had our old ac system replaced last week. System was 11 years old and had a pretty much run its course. Had some significant leaking issues and just really started to become inefficient. We had it replaced last Thursday.

We were looking at power usage today and it seems the new system is even more inefficient. It seems like the new system runs quite a bit more than the other one and we haven't changed what we keep it at temp wise (76 degrees).

Is there any reason that the newer system is all of sudden sucking energy in a major way compared to a decade old system?

How are you measuring energy usage? Are you actually seeing more usage in Kw-hrs or are you just seeing the system run more often?

What is the Seer rating for the old versus new? It's possible your old unit was a better more expensive unit than the replacement.

Have you checked the installation in the attic, it's possible a duct became disconnected.

kWh, although it does seem to be running more. We installed on the 15th. And it's been up ever since. We were out of town from 5th-13th. I can think of any reason why it's up so much.

Looks like the same SEER rating of 15. The old was Carrier and the new is Rheem for whatever thats worth. Same tonnage.

Yeah - looks off at first glance, but really hard to say without more data, ie weather, run profile, what day you actually made the swap (looks like there are some low days as well), etc. I don't think you would see significant difference with the same SEER rating, and as above poster mentioned, checking your ducts is a good start. There are guys that post on here with much more HVAC knowledge/expertise and post regularly.

No clue about old vs new system, but as someone suggested, "Running more" isn't necessarily an indication it is inefficient.

I believe newer systems have 2/variable stages for compressor. So you may have it running more often but at partial speed.

We all want to help but so few facts = guessing.

If you could post
1) the specifications of old HVAC, then new would help (e.g. 36,000 BTU, SEER=8, Heat pump or heat=gas, cool=elect
2) size of living area in SF (on both floors if 2st)
3) power use month questioned, then last year's same month power use
4) did installer use existing ductwork, was it metal, was it a problem fitting new to old


Without that, I can only offer these observations
Our new experience was Jun 2021
Heat pump tonnage DOWN 1T
SEER UP 4
From stage 1 to variable
Same Living SF, same metal ducts, no install problems reported & I was present nearby

• cycling was about the same but comfort much better + gentle breezes instead of jet engine
• energy costs didn't show improvement for a few months but really saved $$$ this last summer when others were complaining

Guessing prior to facts, should they not come forth

• leaks in unit or ductwork, either prior or during install, both unnoticed (suggest insulation if revisited)
• lag in power co monitoring, future reporting to be more accurate in consumption (if you are not doing it)
• smaller tonnage new, perhaps much less than 1T/475SF
• hot, record summer & drought consequences
• installation moved some attic insulation around, needs to be replaced over ceilings
• no new installation inspection, which if not SOP can be done with an annual service plan BUT such a daily spike such as this ... would call in an emergency as possible electric short inside unit (any electricians out there?)
• inferior brand new system vs the old one ... visit Consumer Reports for ratings

tgivaughn said:

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We all want to help but so few facts = guessing.

If you could post
1) the specifications of old HVAC, then new would help (e.g. 36,000 BTU, SEER=8, Heat pump or heat=gas, cool=elect
2) size of living area in SF (on both floors if 2st)
3) power use month questioned, then last year's same month power use
4) did installer use existing ductwork, was it metal, was it a problem fitting new to old

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Sorry for the late response

1) Old AC: Carrier 3.5 ton, Heat pump, BTU 42000 ; SEER=15
New AC: Rheem 3.5 ton, Heat pump, BTU 42000; SEER=15

2) 1765 sq ft (1 story)

3) This is the month in question. Like I said earlier, the new system was installed on September 15th. The dip in the chart is from us being out of town and the AC was set on 82. The beginning of the month the AC was on 75/76.



For comparison, this is our energy from July during that insane 100 degree weather streak.



4) Installation used existing duct work and had no issues putting everything in.

RHEEM needs a semi-emergency call in case there's a short ... I guess.
There's always going to be excessive power consumption on HVAC install & even service days as they run it through its paces BUT that day has passed.

Of course, many other power consumers in your house can be suspect shorting out OR left on/unattended but the calendar fingers are pointing to HVAC, I agree.

TONS/SF right on
Connecting the ducts properly TBD upon the service call suggested that is to check power hookup & consumption.
Rheem has had very good tech support history in Aggieland.

Failing all that, a Master Electrician might have to be Sherlock Holmes here, otherwise you can't afford this new system ....

Appreciate it.

I did get the AC company out last night and he looked for leaks and went through everything. He did adjust the fan speed and refrigerant level. Said to give it a few days to see if the adjustments help. I did ask if the next step was possibly changing the thermostat and that if it was the root of the problem.

Looking at the thermostat history showing how frequently it was running and over the weekend with those big power draws there were times were the AC ran straight for several hours. Yesterday was better even with the guy running diagnostics (in terms of how long it ran).

Obviously we're mainly just frustrated because I'm not sure what else we can do if there is nothing wrong with the equipment.

We replaced our system in July. kWh usage has halved since replacement. Granted we went from a single stage system to a two stage system.

I assume your old and new unit are both single speed?

When it ran for several hours straight were you home? If so, did the temperature feel normal, hot, cold? I'd imagine if it was a thermostat issue and it ran for several hours your home would have been significantly colder than normal?

bco2003 said:

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We replaced our system in July. kWh usage has halved since replacement. Granted we went from a single stage system to a two stage system.

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Yeah, we went from a single stage to a variable. Even with our electric rate doubling, our summer bills have been lower this year than w/ the old unit.