Big F'n Dave Posted August 12, 2008 Share Posted August 12, 2008 My A/C sh*t the bed last Friday. The entire unit (inside and outside) was really old so I'm gonna bite the bullet and buy a new system. I'm trying to decide how much A/C I need. The old unit was three tons. It ran a lot, but it did a decent job of keeping the house cool. I'm trying to decide whether I want to bump up to 3.5 ton. The house is a little over 1700 sq. feet and is decently insulated for its age (built in the mid 70s). Anybody have any A/C ackumen for BFD? Quote Link to comment Share on other sites More sharing options...
geeteebee Posted August 12, 2008 Share Posted August 12, 2008 Methinks you shouldn't be the one making this decision, a licensed hvac contractor should. When I had my units replaced, I had techs come out and tell me that if I got too big of a unit (heh-heh) then the system would not be efficient. It's not a matter of upping the tonage to decrease the amount of time it is on. Quote Link to comment Share on other sites More sharing options...
Big John Posted August 12, 2008 Share Posted August 12, 2008 Calling Chief Dick Quote Link to comment Share on other sites More sharing options...
The Irish Doggy Posted August 12, 2008 Share Posted August 12, 2008 Calling Chief Dick Yes, CD has good advice. Might check into heat pumps if you plan to stay there long term. Quote Link to comment Share on other sites More sharing options...
Gonkis Posted August 12, 2008 Share Posted August 12, 2008 1700 with basement? Quote Link to comment Share on other sites More sharing options...
Big John Posted August 12, 2008 Share Posted August 12, 2008 1700 with basement? No basements in that part of the country. Quote Link to comment Share on other sites More sharing options...
Gonkis Posted August 12, 2008 Share Posted August 12, 2008 Oh, down south. I'm no expert, but I think should go with the 3.5 ton. Curious to see what CD says, but I think it is really dependent on how your house was built, what type of windows, etc. Quote Link to comment Share on other sites More sharing options...
polksalet Posted August 12, 2008 Share Posted August 12, 2008 I thought your kind preached geothermal?? Quote Link to comment Share on other sites More sharing options...
SEC=UGA Posted August 12, 2008 Share Posted August 12, 2008 Methinks you shouldn't be the one making this decision, a licensed hvac contractor should. When I had my units replaced, I had techs come out and tell me that if I got too big of a unit (heh-heh) then the system would not be efficient. It's not a matter of upping the tonage to decrease the amount of time it is on. Believe it or not a higher tonnage can be more efficient so long as you don't go into overkill mode and if the house is decently insulated. This is especially true in two story houses where the ducts have a longer run to cool upper floors further away from the unit (especially if said duct work runs through the attic). Insulation on duct work has become thicker, though. That being said, I forgot how to calculate tonnage per sq ft and can't help out too much. I would think, however, with the new technology and heavier seer rating requirements, that if an old 3 ton cooled efficiently that you will not need to upgrade to a heavier tonnage. Quote Link to comment Share on other sites More sharing options...
chiefjay Posted August 13, 2008 Share Posted August 13, 2008 I'm not CD but I am thinking a 3 ton is plenty and 2.5 ton may work depending on the structure of your house and how well your return air is set up. Quote Link to comment Share on other sites More sharing options...
Chief Dick Posted August 13, 2008 Share Posted August 13, 2008 (edited) Basically it depends on a lot of factors. A decent rule of thumb is about 500 square feet/ton, which would make yours about a 3.5 ton. 1. What style of house do you have? 2. Are you replacing your furnace at the same time? A lot will depend on your ductwork. Typically ductwork is designed with a certain cfm in mind. A 3 ton system will generally push 1200 cfm of air. So a 3.5 ton will be 1400cfm. It also depends on air return, which is a lot more important. Usually going up a half a ton isn't going to hurt you. And with the efficiencies of new units you aren't going to pull any more power than you are now. Some things to check for to see if you have enough ductwork: 1. Count your supply registers. Each one GENERALLY will output 100cfm. So if you have 12, you will push 1200cfm. 3 ton. If you have more than 12, you will be able to push 3.5 ton easily. 2. Check your air return. Usually you will have 2 types if they are on the wall or near the floor. You will have a small one (typically about 14 inches wide), or a big one. (30 inches wide). The smaller one will return about 200cfm, and the big one about 400cfm. Count those, and see what you come up with. As far as price, efficiency, brand name, etc...let me know when you get a couple of bids. And get a couple. I'll let you know if it's a good deal or not, or if you want to PM me your # I'd be glad to give you some good info to ask the HVAC salesman. Whatever you do, DON'T BUY ANYTHING until you talk to me. Edited August 13, 2008 by Chief Dick Quote Link to comment Share on other sites More sharing options...
penguin Posted August 13, 2008 Share Posted August 13, 2008 Marking this thread as I have a 25 year old unit where the compressor is on life support Quote Link to comment Share on other sites More sharing options...
Missoula Griz Posted August 13, 2008 Share Posted August 13, 2008 I know many people who have AC. Most these days dont even turn it on because of the costs and economy. The highest low temp this summer was 63. Last night my wife turned on her side of the electric blanket because I had the room at about 55 degrees at hump time. Love them cold nights. Good loving and fun times in the mountains. Yes, winters do get a little long, but bedtime and a little snuggling make up for it. And, in the summer we get to go outside...deck...stars..coyotes humping..too much info. Carry on.... Quote Link to comment Share on other sites More sharing options...
Jimmy Neutron Posted August 13, 2008 Share Posted August 13, 2008 hump time. Love them cold nights. Ahem... When the weather's hot and sticky That's no time to dunk your dickie But when the frost in on the pumpkin 'Tis the time for dickie dunkin' That is all. Oh, and I installed a 2-ton unit a few years ago in my just <2000 sq ft house and it works well on all but the hottest days. I'd have gone bigger, but my furnace couldn't handle it and I could not afford to do both. I had a buddy's brother get me the stuff at cost and installed it all myself for less than $1k. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.