How do you determine what size central a/c unit a house needs?

[rboyer]

From what I've been told, companies will stop servicing R-22 units since they are stopping production of the stuff.

It's gonna be years before it's totally phased out. Alot of HVAC contractors around here will still service an R-12 system if the owner of it happens to have a stockpile of R-12 laying around and I believe that's been phased out since 1995 and I still see people selling it on ebay and craigslist. I personally am going to be putting a used R-22 unit in the house that I just bought mostly due to the fact that I can service it myself and plan on keeping a jug of freon and a spare compressor for it stored away in the basement.

 

[hvacowboy]

Wow, theres a lot going on in this thread.

In the original question, blue83 asked what size? Well the cheapest answer would be the same as before, unless you want to spend the extra money of replacing the evaporator, and possibly the lineset.

You need to hurry and get a R-22 condensor before the manufacturers stop production, or deplete their inventory.

And as far as deals online, you need a minimum class 1 EPA refrigerant handling license to purchase a condensing unit.

For everybody's information don't be scammed by the dealers saying they can't repair you're R-22 unit anymore, total BS!
Even when new unit and refrigerant production stops, replacement parts will still be availiable, and there will be several options of interim refrigerant options to allow continued operation of R-22 equipment.

 

[hvacowboy]

According to the guys that fixed our heater in the winter and looked over our central air. For a 2,000 sq/ft, we have a 3ton unit. Our consists of high cellings in the living area and master bedroom. 13x double pane windows around the house. As it is, its okay. It will keep the house cool at 72*F in the summer until outside temps start hitting above 88*F, then the house stays around 75*F. When ours goes, we're planning on getting a slightly bigger unit or just a better one.

FYI: A/C units are changing their free-on. They are going from R-22 to something called Pure-on. From what I've been told, companies will stop servicing R-22 units since they are stopping production of the stuff.

You're system operation sounds about normal to me. Most people complain that there unit runs all day when its above 85 during the day, it needs to have long run times to remove humidity.

 

[blue83ranger]

I'm not sure what class my dad has, but he does have some kind of license to deal with refrigerant. He's not a pro though, he just took a class on it in the '90's and mainly does our cars when they have a problem. and he couldn't pinpoint what's wrong with the one we have but he wants a more efficient one anyway.

 

[LittleHorse]

I'm a plus one to suggesting that this is the work for a licensed contractor. A system that is oversized can function just as poorly as a system that's undersized, and there are just too many variables going into it to just go on square footage. Either way, at least in my state, you have to have a contractors license to even buy a condensing unit or refrigerant.

R-22 will be phased out as of Jan 1 2010 - as in no new R-22 equipment can be installed after that date. You can still get service after then, but as the manufacturing of the refrigerant slows down and stops, it will get more expensive, just like R-12 did when automotive systems moved to R-134a.

The new stuff, Puron is I guess a brand name, the actual designation for it is R-410a. The pressures do run significantly higher (typical condenser pressures as high as 450psi or higher) so the entire system must be designed to operate with it. Also you must use synthetic oil rather than the mineral oil from an R-22 system - so if you switch to 410a you will need to replace the indoor unit as well. It's possible to flush the line set between the units to get the mineral oil out, but it's often easier to just replace the lines since the line sizing may need to change anyway. I've only changed one system over to 410a so far and I replaced the line set.


I haven't done the math for an exact number of years, but unless you plan on living in your house for quite a long time, I wouldn't waste the money on getting any higher SEER than the government mandated minimum of 13. The price jumps a LOT as you go up in the rating so you'll have to stick around for awhile to break even, much less realize any benefit. The real ridiculous part is the fact that the design changes they make to achieve a higher rating are extremely minimal in manufacturing cost, so when you buy an 18 SEER unit, what you're really doing is putting the next 8 years of your utility savings straight into their "profit margin" column.

 

[Will]

Biggest problem as a homeowner I've found is the ductwork is generally really bad. Doesn't matter how big the unit is if the air flow is anemic.

 

[LittleHorse]

Biggest problem as a homeowner I've found is the ductwork is generally really bad. Doesn't matter how big the unit is if the air flow is anemic.

agreed. Ductwork design is something equally complex as load calculations, and should be left to a licensed contractor.

 

[Onebadezgo]

When its 120 degrees out here ive seen run up to 700psi and higher especially when you lose the outdoor fan motor. Can get sketchy when you take the gauges off.

Puron is just a brand name developed by the carrier corp. so they can market it to the tree huggers and hippies long before the ban on R-22 truth is countries in Europe(I think i spelled that right) are already moving to ban 410-A in favor of an even "cleaner" CO2 based refrigerant, We're not far behind.

And yes we still fix R-22, R12, and even ammonia systems Bout 98% of AZ runs on 22. we just wont be able to buy fresh R22, Its all recycled now and about ten times the cost it was 5 yrs ago.

 

[LittleHorse]

700 psi exceeds the critical point of R-410a (can't even cross it over on a T-P chart), and the pressure ratings of many of the system components. I don't think it should get that high unless something is very wrong.

 

[skippy]

Littlehorse,Onebadezgo and Will have it right,just call the man.

Oversizing is BAD!

 

[blue83ranger]

it does sound like getting a pro is the way to go. and as far as how long we will keep our house. I know i probably won't be able to afford to build a new house on the same property and I'm planning to live out the rest of my years here, if i can still stand my dad for that long. I'm 26 now so it'll be along while. At least my dad is guaranteed to be here for the rest of his. and if i'm not here then, i'll come back.

 

[skippy]

it does sound like getting a pro is the way to go. and as far as how long we will keep our house. I know i probably won't be able to afford to build a new house on the same property and I'm planning to live out the rest of my years here, if i can still stand my dad for that long. I'm 26 now so it'll be along while. At least my dad is guaranteed to be here for the rest of his. and if i'm not here then, i'll come back.

Just get written estimates,should be free,and then you will know what size you need.Not to mention sticker shock.

 

[Legend]

I can not stress how important it is to have the system properly sized by a reputable licensed contractor.

Sizing is done according to ACCA manual J and takes into account heat loss/heat gain of the structure based on location,building materials,elevation,exposure,etc..

If not properly sized,health issues such as mold can develop.

Most reputable contractors can give a free estimate,which includes a calculation on the trusty laptop.Then get at least 3 estimates.

We will service hcfc-22 systems forever,the refrigerant is being phased out,not outlawed.Puron is the refrigerant of choice for most manufacturers going forward and performs well,but runs almost double the pressure of 22.

I pretty much agree with Skippy. The problem is that like most professions, about 2% of the professionals you encounter are actually competent. (Hence the need to get at least 3 estimates.) Just remember that their real motivation is to sell you a system. Some of them will low-ball the job to make their estimate cheap and get the work, so the system they recommend is poor quality and undersized. Others will go to the other extreme to sell you as much as possible.
I suggest talking to friends about who they use for HVAC and who they recommend. After you get 3 to 5 good referrals for the same contractor - then use that one for one of your estimates.

 

[blue83ranger]

I don't know what for sure happened but i was checking over our old a/c unit to try to see what size it was and all the writing was wore off it. So, for no reason really i gave the thing a kick and we decided to turn it on and see what happens and the damn thing works now. The air out of the vents was 47* for awhile then it stayed at 54* and it still works a few days latter. (we turned it off for a few days) I would assume the kick didn't do it but all that matters is that it works and i think the last time it did was in the '90's. AHHH cool air again, i love it.

 

[skippy]

I don't know what for sure happened but i was checking over our old a/c unit to try to see what size it was and all the writing was wore off it. So, for no reason really i gave the thing a kick and we decided to turn it on and see what happens and the damn thing works now. The air out of the vents was 47* for awhile then it stayed at 54* and it still works a few days latter. (we turned it off for a few days) I would assume the kick didn't do it but all that matters is that it works and i think the last time it did was in the '90's. AHHH cool air again, i love it.

I believe you should have it serviced for the season,which includes electrical check out,coil cleaning,performance check,etc...The unit might need a start capacitor or have a control wiring issue,hard to say without a service check up.

I can usually tell the size of the unit by using the compressor data plate info,primarily the btu/hr rating.