5 ton unit for 1653 sq. feet seems like waaaaaay too much. Not in the a/c business but I can tell you that from what I learned doing research for my own installation, that 5 ton unit may make your house cold, but it will cycle for such a short time it wont pull the humidity out, making it feel very uncomfortable. and as you know, living down here in the south humidity is a big concern. Hopefully some of the more knowledable hvac pros on this site will give you a more difinitive answer to the correct sizing. Good luck.

Manual J load calculation MUST be performed!!!
I just performed one on a 1600 sq house and it called for a 2.5 ton cooling and 60k btu heat. every house is differant as well as location. putting in a too big of a system is waisting money and comfort. You could perform your own, hvac-calc 4.0 lets you do it for $ 50 or find a co how will do it for you and have a copy for you.

3 tons sounds correct unless your house is really leaky and badly insulated. If your house is leaky and badly insulated you should invest some money in insulating.
If you really want to be oversized, then get 3.5 tons. Thats more than enough.

rpfingsten, thank you for the reply. My gut feeling also says that 5 ton seems like too much.

coolmen, forgive me for my ignorance, but what is the best way to find someone who will come out to my house to perform the calculation? I did a search on the web for "manual J residential load calculation" and found hundred of thousands of hits. Quickly scrolling through them, none of the hits seem to be what I need.

neohioheatpump, the house is pretty old (1939), so it doesn't have installation in the outside walls. Also, two of the rooms (living room and family room) have vaulted ceilings. All other rooms have 8 ft ceilings. The house is on pier & beam, so there is a crawl space underneath the wood floor throughout the house.

The living room has two windows on the south side and two windows on the west side, whereas the family room has two windows on the north side and two on the west side. The dinning room has two windows on the west side. The two bedrooms have two windows each on the east side. These windows are single pane. We do have blinds on all of the windows, which helps with the sun.

Just based on your experience, would any of this additional information increase the tonnage, or would you guess that 3 tons is still a pretty good ballpark figure?

"coolmen, forgive me for my ignorance, but what is the best way to find someone who will come out to my house to perform the calculation? "

When you call a contractor, ask them "how do you determine the correct size to install?" If they answer, we have umpteen years in the business, and our experience tells us....yada, yada, or they just replace what's already there, keep looking.

V

I was thinking 3-ton based on the sq. footage. If you have 2 rooms with vaulted windows then it changes. If you don't have insulation in the walls and its not brick that doesn't help either. You should have extra insulation put in the attic if you have an attic in certain rooms.
If your windows are bad, that is something to consider too. 5 tons is just way too big. I guess 3.5 to 4 tons is right. I'd rather be a bit undersized than oversized. Running constantly is not a bad thing if your a bit undersized.

I have 3-tons with 1750 sq. foot ranch with a full basement. 8 foot ceilings. I don't have insulation in walls but I do in attic. I also have all brick. On the hottest mid 90's days it works fine at maintaining cool temperatures. The best solution is insulating not eversizing in reality. My parents house is very underinsulated and their runs alot. And its never that cool.

veesubotee, thank you for your advice; I appreciate it.

neohioheatpump, thanks for the follow-up. There are bricks on the exterior of the house. I went up to the attic and it looks like that we have 6" of insulation up there. You're right about the windows advice...ever since we bought the house, we've been thinking about replacing them. Once we replace our failing A/C (20 yrs old) and the furnace (25 yrs old), we'll be saving-up for better windows.

You reminded of something (that I forgot to mention ealier) when you mentioned your parent's house.... Our home never seems to get below 82 deg F during the hottest months in Houston. I bought a separate thermometer with humidity display as a double check for our thermostat, and the thermometer also matches the thermostat number. I've also noticed that our humidity is in the 60% range in the summer and 70% range in the winter. I'm not sure why that this???

Personally, if you can't get the temperature and humidity down then you need a 'larger' unit. But for Houston, too large would be a big problem with all the excess humidity.

And if you have a separate (gas?) furnace, you should think hard about a heat pump.

You should probably try to fix up the leaks. That humidity with 82 degrees is pretty bad. Maybe you get used to that in humidity.

I personally like 76 and 40% - those are comfortable numbers.

weedmeister, thank you for your advice. I got two bids today (Monday) and they both did manual J calculations. They showed me their numbers on their computer screen. One bidder came up with BTUs that translated to 4.3 tons and the second one came up with 4.5 tons. They told me that they either have to round up to a 5 tons unit or round down to a 4 tons unit. I'm not sure if it's better to round up or round down in Houston. However, now, I understand why the first bidder (on Saturday) came up with the 5 tons number.

The two bidders that came out today (Monday) would like to use a 4 tons unit, whereas the bidder from Saturday wants to use a 5 tons unit. Since I've been getting some good pointers on this forum, I asked them more questions; one of which was 'why such a large number for tonnage?' They said that it's because I have windows with single pane, two of the rooms (living & family) have vaulted ceilings, and the floor is on pier and beam (so it is treated similar to a ceiling in the manual J calculations).

david_cary, my wife certainly agrees with you that the humidity is really bad in our home. :-)

The three bidders that did the manual J calculations said that the new A/C, furnace, and thermostat will work together to keep the humidity under control.

The three bidders that did the manual J calculations want to use a two stage A/C and furnace, whereas the other two bidders (who did not do the manual J calculations) want to use single stage equipment. Of the two who didn't do the manual J, first one wants to use 3.5 tons unit and the second bidder wants to use 4 tons unit.

I'm leaning towards the bidders who performed the manual J calculations, particularly the two who are suggesting 4 ton units. Am I off base here?

4 tons or a 2 stage 5 ton is what i would do.

coolmen, thank you for your reply; I appreciate your advice.

To all who replied to my post,

Thank you so much for your advice and suggestions! I will be getting a new correctly sized AC and furnace tomorrow morning.

unless there are good opportunities to reduce your load calc for cooling to under four ton, you will be disappointed in the comfort level for your home if you elect the four ton.

I much prefer an 80% VS two stg furnace with a qualifying tax credit two stg 5 ton AC condenser.

IMO

If you've elected to go for the smaller size, then you will need to plan on increasing/improving the insulation around the house some time down the road. Sooner the better.

tigerdunes, yes, I'm planning to improve insulation in the attic and put insulation underneath the hard wood floors. Currently, there isn't any insulation under the floors. I'll be doing this project in December. I'll much easier in Houston to work in the attic and the crawl space when it's a bit cooler.

We'll be saving-up for new windows. I went with a Trane XL16i matched system. I wanted the TCONT900T, specifically because I've read your posts in this forum recommending Honeywell VisionPro IAQ (i.e., Trane TCONT900). However, the contrator told me that he called Trane this afternoon and was informed that TCONT900 wouldn't work with XL16i, but it would with XL20i. The XL20i was a bit too expensive for us. So in the end, I agreed upon TCONT803 which is a matched thermostat for XL16i.

weedmeister, yup, I'll be working on that come this Christmas vacation. So far, the house has been okay with the new unit. (We've been using it since 5 PM today (Wednesday).) This is the first time, since we moved into this house, where the humidity is between 43% to 50% (at 78 deg F to 82 deg F). Normally, it would be some number in the 60% range during the summer months. I'm curious to see how it will be in the winter. Usually in the winter months, our humidity is in the 70% range.

I'm hoping that a 4 tons unit will be okay because of two of the three bidders, who took the time to do manual J calculation, rounded it to 4 tons, except one who rounded it to 5 tons.

I'm wondering how well we'll be able to control the humidity in the winter months when the AC isn't running. We start to get mold on our shoes and belts in the closets.

Maverick - you have no insulation above a crawlspace? I missed that earlier if you said it. The crawlspace is one of the most humid places on earth. Foam foam foam that floor. If it were me, I'd pay $600 for one of the tanked foam systems and seal the floor tight. You get 600 sq feet on 1 inch thick for your $600. So you might use 2 cans if you don't mind the $$$. 30% tax credit expiring. You could easily seal the crawlspace with cans of great stuff but I'd use 50 of them or so.

Also - do you have a vapor barrier on the dirt floor. That could be $100 and your time. The plastic should overlap and be taped (mastic?). Even if you have one, it is rarely done right. I'd do this now as it might be a few hours and the crawlspace should be pretty cool even in Houston.

As to the windows - the more cost effective thing is to just use weatherstripping. It isn't going to fix everything but it is cheap.

As to your last sentence. Not to be a wisea##, but you do know they make things for dehumidifying the air? They are called dehumidifiers....Just get a hose attachment and drill a hole to the outside.

fyi: the aforementioned hose attachment is a drain hose, not an air hose.

david_cary, thanks for the suggestions! The canned foam that you mentioned, is it something that I may be able to buy at a store (or is it only available to contractors)? I don't have an special equipment if it's needed.

We don't have a vapor barrier on the dirt floor (inside the crawlspace). I will look at our local hardware store to see if I may buy it there. During different seasons, I have gone into the crawlspace to look around and try to figure out what's going on. The dirt floor is always dry to the touch and pretty hard (dirt is tightly packed). Also, there seems to be good air circulation from the vents. Given this additional information, do you still believe that the crawlspace is contributing to our humidity problem and vapor barrier is needed? (I'll still plan to put insulation above the crawlspace.)

I'll read-up on windows weatherstripping and see how that is installed. Just walking around the house, I can see that some windows have some sort of rubber gaskets around them and others have thin metal frame around them. The rubber gaskets look like that they may have shrank because some of the corners have half inch to one inch gaps while other similar windows don't.

Yup, I've heard of dehumidifiers (although I don't know very much about installing them). But, I'm sure I can read-up on how to install them and get it done if I need to. I'd like to understand the cause of our humidity problem and try to address it before I go and address the symptoms by installing a dehumidifier. So far, the new AC/furnace have been doing a good job. Our humidity level has been around 43% to 55%. (It is set to 50% on the thermostat.) The separate thermometer that I have also has a humidity gauge and it confirms what the thermostat is showing. I wonder how it will be this winter when we're not running the AC anymore.

weedmeister, thank you for the clarification; I appreciate your input!

I guess I'd check the crawlspace humidity with a humidistat. In NC, they are very humid but the ground is bonedry and packed hard. The classic issue here is that the venting is not enough to keep humidity down.

"Great Stuff" is found at Lowes/HD - don't know about local hardware store. The big tanks are more of an internet thing.

david_cary, thanks for the additional information! I'll give that a shot. I do have a humidistat.

We have both Lowes & Home Depot close by; I'll check them out. What are some good google keywords to search for the big tank foam? "foam in a tank" resulted in 4.6 million hits and the first 80 or so didn't look right at all. (I'm new to all of this.) :-)

Tigerfoam. Spray foam DIY kits.

david_cary, thank you for pointing me to Tigerfoam. I found it and plan to use it. Only problem I foresee is that the tank may not fit through the crawlspace enterance. The enterance is 26" long by 10" high and if I recall correctly the tank is 18" by 12".