HVAC problem (undersized unit)

Peace_Maker · Aug 3, 2015

The company that built my home installed a 3 ton unit for a house that is 1900 sq ft. My electric bills are running $300-$350 this summer. I have spoken with my neighbors and their bills are $125-$200. My wife had a HVAC guy come check our system and he said the ducts, insulation, and the unit looked good. When he asked her the size of the house she told him 1400 feet so he said the system was ok. When I came home I reminded her the size was 1900 and she called him back and he said 3 tons was in fact undersized for our house. I do keep up on changing the filters.

This house is only two years old and has good windows and no noticeable leaks. I seriously doubt that going to the builder will yield any results especially this late.

Is the small system the cause of my high electric bills? I keep the thermostat at 74-76 and it pretty much runs constantly. Is a new unit the best solution or could I try a window unit or a mini split in my master bedroom and turn off the vents? Any ideas?

RichardA76 · Aug 3, 2015

I would need to actually see it in person however a 3 ton "could" do it just not real effectively. You may have some options to help with the bill however this year although not near as hot as last year is showing higher bills. There was an increase from what I am seeing from OGE.

doctorjj · Aug 3, 2015

You need to have an energy audit and blower door test done.

If I were closer, I'd come check out your house with my Flir camera.

_CY_ · Aug 3, 2015

Peace_Maker said:
The company that built my home installed a 3 ton unit for a house that is 1900 sq ft. My electric bills are running $300-$350 this summer. I have spoken with my neighbors and their bills are $125-$200. My wife had a HVAC guy come check our system and he said the ducts, insulation, and the unit looked good. When he asked her the size of the house she told him 1400 feet so he said the system was ok. When I came home I reminded her the size was 1900 and she called him back and he said 3 tons was in fact undersized for our house. I do keep up on changing the filters.

This house is only two years old and has good windows and no noticeable leaks. I seriously doubt that going to the builder will yield any results especially this late.

Is the small system the cause of my high electric bills? I keep the thermostat at 74-76 and it pretty much runs constantly. Is a new unit the best solution or could I try a window unit or a mini split in my master bedroom and turn off the vents? Any ideas?

the fastest/cheapest solution to boost your main HVAC is a big honking window unit, Sam's has decent prices.

there are many factors that goes into sizing a HVAC unit .. a pro will do a Manual J calculation ... http://www.loadcalc.net/
you just had an HVAC guy out .. either you trust him or not ..

easiest way to confirm sizing is to ask your neighbors with low bills and same size house and quality of build. there will be a plate on outside condenser with brand/model/size info.

you need to ask HVAC guy that was just out what the subcooling and superheat reading were .. also need to know if your unit uses a piston or TXV? are ducts properly sized?

have you checked if outside condenser has been cleaned? is the inside A coils clean? inside filters clean? hows the airflow?
your HVAC guy should have checked all of above ..

71buickfreak · Aug 3, 2015

I have 2 AC units in my house and I run a window unit all of the bedrooms for personalized control. I'd rather not, but it has to be that way.

Peace_Maker · Aug 3, 2015

Thanks _CY_ the HVAC guy was my wife's cousin and I was not here when he checked the system. I know he changed the filters and he did clean the evaporator, my wife told me he said it was dirty (honestly I did not know I needed to clean it). I'm not sure about the readings. I'll go check the plates on my unit and my neighbors.

saddlebum · Aug 3, 2015

_CY_ said:
the fastest/cheapest solution to boost your main HVAC is a big honking window unit, Sam's has decent prices.

there are many factors that goes into sizing a HVAC unit .. a pro will do a Manual J calculation ... http://www.loadcalc.net/
you just had an HVAC guy out .. either you trust him or not ..

easiest way to confirm sizing is to ask your neighbors with low bills and same size house and quality of build. there will be a plate on outside evaporator with brand/model/size info.

you need to ask HVAC guy that was just out what the subcooling and superheat reading were .. also need to know if your unit uses a piston or TXV? are ducts properly sized?

have you checked if outside evaporator has been cleaned? is the inside A coils clean? inside filters clean? hows the airflow?
your HVAC guy should have checked all of above ..

out side evaporator? a pro would know the difference between an evaporator and a condenser

ConstitutionCowboy · Aug 3, 2015

Our house is over 3100 square feet and our highest bill so far is $198.00. The house is 7 years old. We have two A/C units, one at 5 ton and one at 2 1/2 ton. We keep the house 71 to 73 degrees depending on the humidity.

Look for major air leaks around windows and doors. Check to see if your windows are at least double pane. If you have a real fireplace, make sure the damper is closed when the fireplace is not in use. Make sure bathroom vents and kitchen exhaust vents have flappers that close when the units are off.

Check to see if attic insulation is adequate and that the soffit vents are not covered up with insulation. Make sure you have adequate attic venting at the peaks of the roof. Give all your ductwork a through inspection. You might be inadvertently cooling the attic!

Woody

Peace_Maker · Aug 3, 2015

This should be the plates from my house 1900ft, my neighbors 1825ft, and another house 1875 ft.

saddlebum · Aug 3, 2015

the first is a 3 ton ,the other two are 3.5 ton

HVAC problem (undersized unit)

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