Any HVAC guys in the house?

[AZjeff]

Got an AC tonnage question. My daughter bought a new house 12/15 in Prescott Valley Az. 1600 square feet, 10 foot ceilings, R38 in the ceilings and R18 in the walls. Low E glass. All electric. This past weekend the AC quit working. Got a service guy out from a reputable company, not the original installer. Discovers the coil in the Lennox unit has ruptured. Lennox will send a new coil only and cover no labor or shipping. He suspects the coil was faulty but over work could have contributed to the failure. Also the HVAC guy is telling daughter that this unit is way undersized for this house and likely the electric furnace is also. She works with a woman who's husband is with this company so she doesn't think she's being upsold or whatever.

Can anyone tell me based on the specs of her house I listed what size unit would be appropriate or do you need more info? Curious what a disinterested informed party would say was correct without knowing what was installed. Are there industry standard formulas for HVAC sizing? thanks Jeff

 

[Jimzz]

What type of insulation is in the attic? Is the air handler in the attic or living space? And what is the SEER rating? Is the duct work in the attic or wall?

You could get by with a high efficient 2.5ton in many cases. Without seeing I would lean toward a 3ton myself though.

 

[Leo99]

A quick Google search says 3 tons for 1500 to 1800 square ft. Maybe the 10' ceilings in AZ push that to 3.5 tons but with that good insulation it might even out and 3 ton is the correct size.

 

[zuluplus30]

I just stepped up from a 2.5 10 SEER to a 3 ton 16 SEER. House is only ~1300sq/ft but very poorly/cheaply insulated. 2.5ton wouldn't keep up when heat went above 93. 3 ton was definitely the solution for us.

 

[Nick1994]

My A/C was having some issues and I was doing some research on A/C units the other week. In Phoenix it looks like A/C are often sized for 400 square feet per ton. My house is 1,400 square feet and has a 3-1/2 ton unit. Was just low on refrigerant because of a leak. A top off and it runs perfect now.

I'd say in Prescott Valley probably 450-500 square feet per ton, but I'm no expert. A 3 ton unit would probably be ideal for your daughter.

If it helps others Prescott Valley is a pretty warm climate. Almost no humidity and it can get to around 100'in the summer, some days maybe slightly higher. Not Phoenix climate though.

 

[dishdude]

Sounds like my house, the builder originally put a 3.5 in and I had it replaced with a 4 ton unit and feel it's sized right.

I've never heard of overworking a coil.

 

[SZR48207]

The 500 sq ft/ton rule is pretty common where I'm located also (OK).

However, the correct way to know tonnage is to do what is called a Manual J Load Calc. It factors in many many variables, but most of the old school HVAC companies don't do 'em and just work off of the easy rules.

But regarding your daughter's house - I would not automatically assume that you need to upgrade to more tonnage.

Undersized units tend to be more efficient and longer lasting because they cycle on/off less. In humid areas, a system that runs longer does a better job of reducing indoor humidity which makes it more comfortable indoors.

I know humidity isn't a factor in AZ, but she may be able to do some simple measures on the house to reduce the cooling load. Tinted windows, improved attic ventilation, air-sealing of wall penetrations, and dark drapes can all make a drastic difference.

If the backyard faces west or south, hanging a outdoor patio shade from the ceiling to block light from reaching the house can also do wonders.

 

[JustinH]

Had a 2.5 ton 14 SEER unit installed in Central Texas a couple weeks back.

House is 1040 sq feet.

 

[bioburner]

The intense heat and duration(100 even at midnight) of it has been a trial on most adequate systems in southwest this year. Insulation is the fastest payback on home improvement. I have r60 in the roof. Reddy is right about cycling of the units and getting out moisture that's more of an issue here in MN. Insulated drapes help a lot and are not that expensive and rewards both heating and cooling bills.

 

[AZjeff]

Thanks guys. This is a BRAND NEW house. One would hope it was spec'd with the correct size heating/cooling and the AC unit wouldn't fail going into it's 2nd cooling season. Not impressed with Lennox at this point. They're frugal with their resources, I've never seen the thermostat below 78 in the summer or over 66 in the winter so they aren't asking too much of it. All windows have insulated drapes.

More info: attic insulation is about 14" of white blow in, the air handler and ducts are in the attic and SEER unknown but will find out. She has noticed that it seems to run a lot but always keeps the set temp. This might be what Reddy45 mentioned about an undersized unit.

Her area sees 100 on the hottest days but certainly not at midnight.

 

[dishdude]

How many tons is the unit?

 

[AZjeff]

Originally Posted By: dishdude
How many tons is the unit?


2.5ton don't know SEER yet.

 

[NStuart]

My house is 1500 sq ft open floor plan.we just renovated( full gut job) spray foam in walls and attic. Complete new a.c. system and ducts. We went from a 16 year old 4 ton down to a 16seer 2 ton. Our house is "L" shaped with a 450 sq ft master on the short side of the L. The master is farthest from the air handler. A.c. freezes you out in the entire house except for the master and thermo is set on 73. We turned the fan speed up and ran a dedicated duct. We live in savannah ga so it gets hot here too our a.c. doesn't exactly run constant and the bedroom gets a little stale but not bad. My point is the good insulation and small unit has great potential

 

[NormanBuntz]

I'd be ragging on the home builder for using an HVAC company that installed an undersized unit with possibly a damaged coil. Maybe the squeaky wheel gets the grease.

 

[i_hate_autofraud]

A "overworking coil" that burst is really a defect in the tube at that one spot, these copper
tubes are stretched and work hardened a lot during forming, so you have a 1 in a million that was going
to let go anyway!

If this A/C was run in a cold ambient on purpose, it's possible to return almost liquid freon
to the compressor that would over pressure the outdoor condensor coil, also a 1 in a million
since they're mostly designed not to do that.

 

[AZjeff]

Not exactly sure what you said but the HVAC guy she had look at it said it's a defective part.

 

[hemitom]

2.5 ton condensing unit is to small for a 1600 sq ft home with ten foot ceilings and r 38 insulation in the attic, in your climate.
If the house had a better r value you might get by with a 2.5 ton

 

[North to Alaska]

Did the fella that is doing the work perform a manual j calculation?
Simple solution to her problem, get 3 or more hvac companies out to give an estimate.
Don't ask them to do a manual j calculation.
If they do it on their own, go with those bids.
There are MANY factors that go into figuring out what size unit she needs.
New home builds are notorious for undersized ac and furnaces. Lowest bidder.

Also an even better question to ask her...does the house ever get warmer than what she sets the temp at? If yes then it is undersized. If no then it isn't.
You want a unit to run most of the time. An oversized ac unit is much worse since it will cycle on and off more...and that is whats hard on the ac.
The tech that said that her ac is overworked is full of [censored].

Definately get multiple opinions.

 

[Linctex]

Most new homebuilders in Texas offer a warranty on the home.

Did she have any kind of home warranty?
I can't imagine a respected homebuilder would regularly hire subs that install inadequate equipment.

2.5 tons is fine if there was more insulation.

 

[North to Alaska]

Originally Posted By: Linctex
Most new homebuilders in Texas offer a warranty on the home.

Did she have any kind of home warranty?
I can't imagine a respected homebuilder would regularly hire subs that install inadequate equipment.

2.5 tons is fine if there was more insulation.


Key word here is "respected"
I am the unhappy owner of a 1.5 ton ac installed by builder. Should have been 2 ton.
Gets into the 90's and it can't quite keep up. Added anotther 8 in of cellulose insulation to bring it to r49. That help quite a bit.