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

[wonder88]

We just bought a new 3300 sqft 2-story house from David Weekley.
And recently we found out they are using only one AC unit (5 tons) for the house. We feel really suprise becasuse we saw most of new houses at this size have 2 AC units. We checked our contract with the builder, and there isn't any word about AC. We also discussed with the bulider, and they said this design past some model-based performance test, so they chose one unit.
All the model homes from this builder using 2 units, even for one story home (~2500 sqft).

We are worrying about the quality and efficieny of this design, and also we heard that one unit will produce a bigger eletric monthly bill for us. The new house is almost done, so it is very difficutl to change to 2 units.

Can anybody help us on this to give a professional analysis or conclusion?
If it does make big difference or affect the re-sale value very much, we might return the house to the builder.

Thanks a lot.

[phsm]

thats really close it should a least be zoned. That will help a little

[wonder88]

Thanks a lot for your answer!
It is 2-zone system. Is that very popular to use 2-zone AC for such a size house? (~3300 sqft)? It's my first time to buy a house. I just feel not confident with the 1 unit 2-zone AC system and also worry a little about the re-sale value.

thats really close it should a least be zoned. That will help a little

[dash]

Thanks a lot for your answer!
It is 2-zone system. Is that very popular to use 2-zone AC for such a size house? (~3300 sqft)? It's my first time to buy a house. I just feel not confident with the 1 unit 2-zone AC system and also worry a little about the re-sale value.

Your builder is well known for quality and energy effiecent construction.Zoning done properly will provide low energy costs.

We used to do work for a competitor of your builder.Our nightmare was explaining why the energy bill for our job ,was twice the monthly amount ,compared to the David Weekley built home next door.

Our builder homes needed 7.5 tons compared to the Weekley home that was 4 tons.All due to the insulation and window/door differences between the homes.Plus the Weekley home had higher then the mininmum required SEER .

IMHO. You can rest assured that your new home will be fine ,or your builder and HVAC contractor will make right.

[RoBoTeq]

Your builder is well known for quality and energy effiecent construction.Zoning done properly will provide low energy costs.

We used to do work for a competitor of your builder.Our nightmare was explaining why the energy bill for our job ,was twice the monthly amount ,compared to the David Weekley built home next door.

Our builder homes needed 7.5 tons compared to the Weekley home that was 4 tons.All due to the insulation and window/door differences between the homes.Plus the Weekley home had higher then the mininmum required SEER .

IMHO. You can rest assured that your new home will be fine ,or your builder and HVAC contractor will make right.

I'm not aware of this builder, but if they are good by dash, then you should have no problem. I gave the same basic answer on your other thread without knowing the status of this builder.

[sarge]

Keep in mind that when those homes with 2 systems start to have replacement issues, they will be purchasing 2 condeners, 2 evaproator coils and two furnaces, while you will only have to replace 1 when the time comes.

Plus maintenance, only one unit to maintain.

[wonder88]

Thanks a lot for all these professional answers! I really appreciate that.
I live in Houston. I only know the the system will have two zones (downstair and upstair), and the brand is Lennox. I don't know if the AC has 2 stages.
After I talked to the builder about my concern, they offer me to install a Honeywell F100 Media Air Filtration System and two Honeywell TH8321U1006 VisionPro Programmable Thermostat with Dehumidification Controller. I don't know how these upgrades will help.
By the way, do I need to check with them about the stages of the HVAC system?
Again, thank you a lot for your help.

[dan sw fl]

I live in Houston. I only know the the system will have two zones (downstair and upstair), and the brand is Lennox.

After I talked to the builder about my concern, they offer me to install a Honeywell F100 Media Air Filtration System and two Honeywell TH8321U1006 VisionPro Programmable Thermostat with Dehumidification Controller.

Zoning done properly will provide low energy costs. ... like DASH states.

Hopefully, your mechanical contractor KNOWS Zoning.

The noted HNY t-stat will provide good humidty control.

Sizing and 2 stage issues can only be responsibly answered after Manual J Load Analysis in performed for YOUR house given the Window and Insulation Specs and house orientation.

[wonder88]

Thank you for the answer. I hope they will do the right job.
My wife is considering to return this house because of the one unit.
It looks we are over-react to it.

Zoning done properly will provide low energy costs. ... like DASH states.

Hopefully, your mechanical contractor KNOWS Zoning.

The noted HNY t-stat will provide good humidty control.

Sizing and 2 stage issues can only be responsibly answered after Manual J Load Analysis in performed for YOUR house given the Window and Insulation Specs and house orientation.

[pstu]

It matters a lot that you are in Houston. My house may not be too far from yours, if you are buying out West where tons of building is going on. It is 3400 sqft but single story, built in 1989 with single pane windows. My Manual J calc says I should get by with 4.5 tons (delivered to the registers), even though the house has 2 units and rather more nameplate tonnage. Rather to my surprise I think there is evidence 4.5 tons would do the job for my house, provided the airflow can be delivered to where it is needed depending on the time of day. One AC system runs 70% during the day and the other runs 50-60% during the night (I was very surprised to learn this).

So it is not out of the question that your David Weekly home can work OK with 5.0 tons. There are many ways to screw it up, but if done right it should work for you. I would not agree with your wife that simply having 2 units makes things right, it *will* mean double the costs for maintenance. Eventually you will have to replace both units, and they won't last any longer if you have two of them. Your energy bills should be the same whether you have one unit or two. This good news about David Weekly homes being more energy efficient is news to me though, hope it works out for you.

Heck the way the building industry is faring these days, you might try pounding the table and trying to extract a price concession from Weekly. There *is* an oversupply of houses this year.

Hope this helps -- Pstu

[alex870]

For comparison, my house is a 4250 sqft 2 story in DFW built in late '05, it has 8.5 tons split as ~ 3.5 upstairs, 5 down. It struggled when the outside hit ~108, otherwise it's fine. I have all the usual energy star rated stuff - plenty of insulation, low E windows etc. It's amazing how much lower my AC bills are compared to family and friends in smaller houses built 10 years ago (and they keep their AC 5 degrees warmer).

It seems like you might be on the low side for capacity for TX. There are definitely minuses of 2 units, but a big plus is when 1 breaks you still can run the other to avoid complete cooling loss (hopefully it's not 108 outside at the time!). That said, a mini split might be a nicer & better option, if you have a specific room you tend to use in isolation for periods of time. (Media room, home office etc).

I have a 1 ton window A/C on my home office (faces rear of house so HOA doesn't mind) and a 1 ton 2 pipe floor standing unit that I use either in my gym or media room. I'm considering a mini-split for my media room as it's west facing and needs spot cooling to be usable. Something similar may work for you.

[wally01]

It sounds like the unit is too big to me. You should only need 3 to 3 1/2 ton of A/C for that size home. Return the A/C not the house.

[udarrell]

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

Could something need some work?
I agree with wally01, the 3.5-Ton for the original post should be closer to a J calc.

What does a Manual J say? - udarrell

[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.....