new ac unit

[Herkie Walls]

I need a new AC unit in my house. We are going to upgrade from a 2.5 to 3 ton system. The duct work has been upgraded for the 3 ton. Does anyone know if $2,300 installed is a fair price for a R22 unit. I trust the guys that gave me the quote and they have done good work for us for 5+ years.

 

[midtown]

Why did you up your tonnage? Did the A/C people measure your house and calculate that 2.5 was too low? What SEER rating?


The below response is why I asked. Unless you added sqftge or the unit was designed wrong in the first place thats a bad idea.

 

[accuratehorn]

"Upgrading" tonnage is not an upgrade, unless your house needs the extra tonnage. Each system is designed for an appropriate tonnage. More just wastes electricity.
Here's what happens: the house cools down faster and the system shuts off. It never dehumidifies the house. It shuts on and off more than they appropriately sized system, which actually uses more energy than a smaller system running longer when it is on. The smaller compressor uses less energy to run compared to a larger one.
There is a guide to sizing systems for houses which a qualifed A/C engineer, or someone trained to do this, can decipher this guide and apply it to your house.

 

[brntorng]

Timeout.

Arbitrarily raising the tonnage is not a good idea. The AC unit needs to be matched to the house--not too big or too small. If it's too small it won't cool adequately. If it's too large it won't dehumidify properly. Many contractors use various "rules of thumb" to determine the proper size, but there's only one right way: a heat load analysis of your house. Some contractors offer this as a service, but most don't because it's over their heads or they don't want to take the time since it's not as profitable as just winging it. (It's included in their training to get licensed, but most don't remember how to do the calculations.)

Perhaps a comprehensive analysis has already been done which would be good, but if they haven't done it or don't know how, you should be able to hire an independent HVAC engineer to run a computer analysis for you. This should also include an analysis of the ductwork to make sure all the drops are properly sized for each room, the return air path is large enough, and the air handler is the right size. Should cost around $200 or $300, money well-spent considering how much you'll be spending and how long the unit will be in service.

Get some competitive bids if you want to know if it's a fair price. If you're in Austin I can PM you the name of my AC guy who does great work for a very reasonable price.

Are you replacing the inside unit as well as the outside unit? (At that price it doesn't sound like it.) If the inside unit (especially if it's more than a few years old) and the outside unit are not matched, you won't get anywhere near the SEER rating of the new outdoor unit and you'll be missing out on most of the financial benefits of a high SEER outdoor unit. Again, the HVAC engineer can point you to the properly matched system for your house. Again, if you're in Austin I can point you to the HVAC engineer that did my analysis for me.

I upgraded two complete systems (upstairs and downstairs) last year after doing a heat load analysis and the results are impressive. Our house has never been so comfortable. And guess what, the original systems were both improperly sized and contractors I got quotes from prior to hiring the HVAC engineer all recommended improperly sized units using their "rules of thumb".

 

[Herkie Walls]

the indoor unit was replaced last year. This unit is for the upstairs area of the house which is appr. 1600sq ft. The upstairs unit has never cooled the house properly for the 4 years that we have lived in the house.

 

[brntorng]

HW, you're making it sound like you want to know if 3T is appropriate for 1600 sq ft of upstairs space. That's not nearly enough data. A heat load analysis will account for where the home is located (to account for environmental heat and humidity), wall insulation R value, ceiling insulation R value, window size and type, window shading, window exposure, duct sizes and locations, air vents, duct insulation, floor plan, return air path, air handler size, filter type, ceiling height, appliances, etc. It could be that 2.5T is adequate cooling capacity, but your ductwork was inadequate due to size, location and/or, insulation. It could be nothing more than an undersized return air grate or a kink in a freon line. Or maybe your old 2.5T system wasn't performing up to spec. Getting HVAC systems done right is an engineering problem with an engineered solution. Hire an engineer and get it done right unless you want to just throw money at the problem without knowing if it's the right solution. Don't you see a dentist, medical doctor, mechanic, plumber, etc when you need a specific problem solved?