3700 SQ FT home in San Antonio

[SANDMAN_SATX]

I am building a 3700 SQ FT, 2 story home in San Antonio Texas and would like to know if two 14 SEER Goodman units (4 ton and a 2.5 ton) will be enough.

Thoughts?

[amd]

New-construction-must-do-room-by-room-load-calculation-to-properly-design-system-no-exceptions!.

*Any contractor who uses rule of thumb sizing for new construction has no business selling equipment.

[SANDMAN_SATX]

Understood but my builder is doing a load calculation. I simply wanted to know if the units per size of sq foot sounded ok or not even close. I've been screwed by a builder in the past....

[amd]

I'm not sure how well houses are built in texas (attic insulation?), how hot it gets, how much window surface area there will be, or if the builder is going to (foolishly) put the ductwork into the attic, but 6.5 tons sounds like a lot of cooling for 3700 sq ft.

[beenthere]

I'd say wait until you see a load calc. Along with all its input. And then ask if its sized right.
Your area has a low latent load.

[Thurmont HVAC]

Have at least 3 contractors do a load calc and give price. compare, ask questions then pick one.

[SANDMAN_SATX]

AMD,

All builders in Texas put the duct work in the attic. The house is a "green home" which means it has low -e- glass windows, soffit vents and radiant barrier (tech shield).

[HVAC Teacher]

Agree with load calc. but shootin from the hip seems like a lot - maybe not if you have a lot of glass.

Remember I'm from a different part of the world. How in the world do you Texans stand that heat?

[teddy bear]

I am building a 3700 SQ FT, 2 story home in San Antonio Texas and would like to know if two 14 SEER Goodman units (4 ton and a 2.5 ton) will be enough.

Thoughts?

Sorry, we can not help you until you get to much a/c. I like to deal with the finer points like get adequate fresh air into the home when occupied to purge indoor pollutants. Also keeping the home <50%RH during wet cool weather. I suggest that you get a large enough a/c to maintain the temperature you want during the hottest days with the home occupied by however many of you there are. Than add a ventilating dehumidifier to provide the fresh air. During hot weather the a/c will maintain the temp/%RH you want. During the cool weather when the a/c does not cool much, the dehumidifier will remove the moisture. Fresh air and dry even during wet cool weather or no a/c operation. There are several brands-Ultra-Aire/Honeywell/Rhem etc.
Regards TB

[beenthere]

Even his cool days are hot compared to most areas. Doubt he needs a dehumidifier if the A/C is sized right.

[SANDMAN_SATX]

The saga continues. The A/C is cooling my new home but I can only get the temp down to 75 degrees on a 100 degree Texas day. I really appreciate it if you could help me answer some of my concerns below:

How cold should the air be coming out of the vents if the temperature at the intake is 77 degrees? I measured he air from a vent and it read 66 degrees which i thought was too warm. I seem to recall that 18 degrees cooler than the intake is what it should read.

How cool should the attic temperature be compared to the outside/inside of the home? The home is a green home so i have radiant barrier.

The upstairs does not have any returns in any of the room (bedroom and theater/game room) and i thought this was odd. Should I be concerned?

The home is a two story home and my 4 ton unit cools the downstairs while the 2.5 ton cools the upstairs. This has me worried since I thought having a bigger unit cooling the upstairs would make sense since heat rises (tall ceilings). The sq footage is comparable between upstairs and downstairs.

Thanks in advance!

[andserco]

If you need a second opinion on your systems, contact "sarge" on this forum..He is in S.A. not sure of his coverage..

[cturman]

I live in Tx with a 3600 sq ft and there is no way the upstairs should be smaller. Check which is running.

I have 2 2.5 ton units and i can barley get to 76 upstaires on the recent hot days. 74 at night is no problem

My house faces south which really helps on the sun heating in the summer.

[amd]

The saga continues. The A/C is cooling my new home but I can only get the temp down to 75 degrees on a 100 degree Texas day. I really appreciate it if you could help me answer some of my concerns below:

Sounds pretty good to me.

I doubt you need more cooling - might want to ensure that the ductwork is sealed/insulated, refrigerant charge is correct, and possibly possibly look into topping off the attic insulation. (Not sure what minimum code is there, but it would be wise to have R40-R-50)

"Green home" means nothing.

[TxTurbo]

18-20 degree split on a 95 degree day with 50% humidity (design temp). The hotter and/or more humid it is outside, the lower that split temperature will get.

Do you have a copy of the heat load calculations that were done? I would be very interested to see them. It sounds like your systems may be undersized, but I'd need to see the load details before making a definitive statement.

What's the indoor humidity like? 75 degrees @ 60%+ humidity would feel very sticky and warm.

[seatonheating]

18-20 degree split on a 95 degree day with 50% humidity (design temp). The hotter and/or more humid it is outside, the lower that split temperature will get.

Do you have a copy of the heat load calculations that were done? I would be very interested to see them. It sounds like your systems may be undersized, but I'd need to see the load details before making a definitive statement.

What's the indoor humidity like? 75 degrees @ 60%+ humidity would feel very sticky and warm.

Good points but I doubt a heat load was ever done on his home. He came on here months ago asking for sizing per sq. ft., didn't get the answer he wanted, and left.

If that is truly the case then..well.....

[beenthere]

The saga continues. The A/C is cooling my new home but I can only get the temp down to 75 degrees on a 100 degree Texas day. I really appreciate it if you could help me answer some of my concerns below:

How cold should the air be coming out of the vents if the temperature at the intake is 77 degrees? I measured he air from a vent and it read 66 degrees which i thought was too warm. I seem to recall that 18 degrees cooler than the intake is what it should read.

How cool should the attic temperature be compared to the outside/inside of the home? The home is a green home so i have radiant barrier.

The upstairs does not have any returns in any of the room (bedroom and theater/game room) and i thought this was odd. Should I be concerned?

The home is a two story home and my 4 ton unit cools the downstairs while the 2.5 ton cools the upstairs. This has me worried since I thought having a bigger unit cooling the upstairs would make sense since heat rises (tall ceilings). The sq footage is comparable between upstairs and downstairs.

Thanks in advance!

So what indoor design temp was used when they did the load calc?

What was the heat gain the load calc said the second floor has?

When you say the first and second floor are of comparable size. Do you mean each floors sq ft of space. Or each floors sq ft to ton ration.

[SANDMAN_SATX]

Attached are the load calcs for upstairs and downstairs.

[beenthere]

By the load calcs. Your home is 3400 sq ft.
Your first floor is 376 sq ft larger. And apparently, has much higher ceilings then your second floor. So it should have a larger unit then your second floor.

According to the load calc. Your A/C was only sized to be able to maintain 75 inside when its 100 outside.

[SANDMAN_SATX]

I just found out that the builder used a plan almost identical to mine to perform the load calc. All of the rooms are virtually the same but my house is basically 93 sqft larger that the plan they used for the load calc. The extra room is in the gameroom and down stairs master bath.