Only one 5 ton AC unit in a 2-story 3300 sqft new house, please help!

[Craftsman]

I have never heard of returning a house, but I guess with the right legal counsel you can do anything these days.

I would invest in getting a complete set of drawing/plans from the builder of your model. On those plans should be the HVAC design—if not, request and pay for a set of plans for the HVAC too. That will give not only you, but everyone here will have a better idea of what you purchased. All these plans will be invaluable in the future. Do not expect to get these plans for free.

[edward301]

I know of David Weekly homes, he did, and may still build here in Austin, TX.
Never heard of any complaints with them.

5 tons should be more than enough for 3300 sq ft. I have a 4000 sq ft
home here in Austin, TX and have a 2 ton unit, and a 2 1/2 ton unit. Both
do fine, even last summer when we had 2 weeks of 100+, they kept the
house at 73 during day, and 70 at night with no problems. If your
new home is energy efficient, and most have to be, you should be
fine with 5 tons.

[pstu]

I submit it may be worth the effort for Wonder88 to download Hvac-Calc and get his own copy of Manual J calculations. The price is really nominal, especially when you consider how much is riding on this decision.
http://hvaccomputer.com/talkref.asp

If you need some assistance, you can email me with the address in my profile, and we can talk on the phone. I am sure you can do this, probably more sure than you yourself are. It's really not that hard just a couple hours work measuring things.

Conventional wisdom in Texas tends to say your tonnage is light, we have modern Texas homeowners saying it looks OK, and we have experienced pros from near the border (the "other" border) who are urging us your tonnage is too heavy. The only way to really decide this before moving in, is to get a competent Manual J calculation done. I hope you will consider it.

It might be worthy to ask the David Weekly representative what design conditions are for this home. I would expect something like 94F outdoors, 75F indoors, and 50% indoor RH. If they can say this, they might be willing to put in writing some kind of guarantee of performance. That would be golden if you can get it, some AC installers have offered a written guarantee as part of their (very expensive) proposal. Perhaps David Weekly has a fine reputation, but I feel queasy trusting any home builder to do the right thing a year from now if you are dissatisfied.

Best of luck -- Pstu

P.S. Upon re-reading, I think Craftsman's idea is an excellent one. You can do a lot in the future with documentation like that, and it might include the specs you need for AC.

[alex870]

Alex870, it is difficult to believe that you need that much tonnage in he DFW area.

Dallas is usually hotter and the humidity lower than the more southern TX cities. Houston is all about humidity, so I'd say not oversizing is far more critical there as you get conditions like 98F and 95% humidity outside and you need serious moisture removal.

With my AC, they do seem to have sized it for worst case scenario, but the duty cycles during avg temps aren't unreasonably short and the indoor RH is around 42-44% throughout summer. So if 8.5 delivers what's needed, I can't knock it. Anything less than 105 outside seems like there's ample headroom left in the system.

Could something need some work?

Unlikely. If I had efficiency issues, my bill would regularly bust $400/mo for a building of this size and my cool tendencies. My units could use some TXV's on them though.

I agree with wally01, the 3.5-Ton for the original post should be closer to a J calc.

Agree - better to stay close to the J calc figures and run long duty cycles for a high humidity climate. Get a mini split for 1 or two west facing rooms later on if really needed - the flexibility of individual room control is nice, esp if you have a home theater or a room that is sometimes unusually warm.

[mark beiser]

I hope your builder is building homes better now than they were 10-15 years ago in my area.

[udarrell]

I like the way you formatted those quotes, - copy & paste?
Your posted comments were very good, but it is DFW, not Houston.

The (DFW) Dallas/Fort Worth area is relatively dry & that is why I was guesstimating that, less tonnage ought to match a manual J.

I use a half-ton (6,000-BTUH) room AC on a first main floor that is close to 850 to 900-sf in an old 1937 farm home. That is over 1600-sf per ton!

Even at 103 & 104-F Heat Index, the way I have it setup it does the job.
This home is loaded with windows & not a lot of shade.

My electric bill with electric hot water heater & electric range, etc., is about $45.00 a month through the summer.

Photo of home & the info on the Room AC setup:
http://www.udarrell.com/aircondition..._charting.html
- udarrell

[jmiles]

It is cheaper to run 2 small units rather then one large unit. Even if the system is zoned balls on . Especially if we are talking about a single stage unit.....

[pstu]

It is cheaper to run 2 small units rather then one large unit. Even if the system is zoned balls on . Especially if we are talking about a single stage unit.....

Jmiles, what is the reason you say this please?

Best wishes -- Pstu