What are you basing the size of your unit on? The HVAC sub should have done a manual J and determined what size system was needed. Was this done? If not, how did he decide what system would be most efficient in the house as built?

You can get more information on the HVAC forum here.

Here is a link that might be useful: Heating & Air Conditioning Forum

He says he did the manual j and came up with a 5 ton system.

It would rarely (probably never) be worth the cost financially to switch out a new seer 13 unit.

Now - not having a zoned system when you wanted one may be worth the money to you to change out but it would be cheaper just to add the zoning.

Variable speed is very nice and maybe able to be handled without changing out the system.

Everyone loves to talk about efficiency but in the end you want to spend the least and use the least amount of energy. Far and away your most important issue is solar gain. Control your solar gain better and you will more than make up the difference between seer 13 and 16. Plant a few trees....

I agree with david. Depending on your electric cost, the savings between 13 and 16 may not have even be worth the pay off if it had been installed origionally.
Efficient design starts with the shell and the home design, windows, orientation, etc. You should not rely on mechanical means for efficiency. Shading windows either exterior, interior will reduce the cooling demands. A tight shell was a really good start (all though foam rarely pays off in walls). An ERV should have been included in the design to begin with most likely.

Do you have anything in writing stating what is included with your system? Signed change orders in writing amending the original contract docs?

The only way to get the attention of a bad builder is to not pay him.

Your difficulty is an example of a common misuse of an Allowance. An Allowance is for Work that for some reason cannot be fully documented before the contract must be signed but the design of the HVAC system should be part of the base price and anything in the base price should be described in the contract. In other words, there is no reason that the design services offered should not be described in some detail and be included in the project schedule...you got a project schedule didn't you?

13 SEER unit instead of the 16 SEER, variable speed, and zoned unit.

that is a big difference. in Texas, like in La. humidity
is a factor. the vs would have helped to control humidity.
getting the minimum efficiency hvac..as much as we depend
on hvac would be unacceptable to me.

of course I sent back the 14 seer unit the supply house
sent me for the 15 seer unit I had ordered.
as your hvac will last for 12-15 years, you have to
factor in comfort and what it will cost you for the
13 seer as opposed to the 16 seer.

you say you added gas tankless water heaters..where
are they installed? exterior of house?

hvac contractor could resell 13 seer. happens
all the time. now you have top of the line furnace
and lowest hvac. doesn't make sense for a cooling
climate.

just as you invested in insulation (agree with
you about the walls lz) the hvac choice should
have been consitered just as importantly.

as far as your load calc..divide tons installed
by sq ft of house. got 500 sq ft per ton?
that is what it sounds like to me. hope I'm wrong though.

best of luck.

to say it is builder ignorance is unfair.
you also had a say in the process.

it would be fair to say that the ball
was dropped by builder, hvac company
and homeowner.

energy rater:

you are right it was my fault to let it get that far along. But I made it know from the beginning that I wanted input on the design and I asked about it several times during the process but didn't get a response.

The house is a 3130 sf home with 10' ceilings throughout. I don't think he used a 1 ton/500 SF ratio.

I guess the question I have now is is it financially sensible to pay for the new system (A/C?

The house faces NE(front)/SW(back). The placement of windows was very well thought out during design with our architect. What windows do face the SW we have planted shade trees to combat the remaining effect of the heat. We had a blower door test run (reverse pressure) and it came up with a 2.62 ACPH. I don't really know how to interpret this other than to relate that the typical new home this tech says he works on are getting 5-6 acph.

We don't have that many windows, though the ones we do have are large. They are Low-E, Argon gas filled, tinted.

We tried to make the right choices.

you did. the ball just got dropped on the a/c portion.

talk to the builder & hvac company. together, nicely.
explain to them what you have to us.
even the hvac guy would have to agree that top
of the line heating deserves better than minimum
efficiency single stage a/c.

at 626 sq ft per ton (not 500 sq ft per ton rule of thumb)
the variable speed a/c will run in low speed and
remove humidity. the single stage unit runs full
blast all the time, shortcycles & doesn't remove
humidity.

it is your comfort at stake.
in our cooling climate we run a/c 8 of 12
months.

did anyone speak to you during the process
about adding fresh air? whole house dehumidifier?

don't beat yourself up, but do make an effort
to get the better a/c for your new home.
like I said in my first post..hvac company
can easily sell 13 seer to someone else.

best of luck.

full spray foam and still only 2.62? Sounds like the foamers missed some spots. Still good though. Good enough for Energy Star 3.0 certification.

If you really have shaded well, then 5 tons is too much. My experience is that they never count on shade trees - for good reason I guess. So you will have an oversized single stage unit in a humid climate - not great.

I'd talk to the builder. I had a 4 ton changed to a 3 ton at no cost to me because they screwed up. Seems like you can get a discount or free changeout. Mine was changed out 30 days after move-in. I am sure the unit can still be resold at no discount to an unsuspecting customer ... the practice is probably commonplace. If they were honest, they could just offer an extra year warranty and anyone would take it.

5 tons for a well designed and shaded 3100 sqft house is too much - even in Texas.

there is no shade today. just 3" caliper trees that might produce shade in 5-10 years.

Is your furnace variable speed?

Five ton sounds big, you have closed cell foam, but again you have 10 ft ceilings.

Ask hvac dealer what it would take to replace A/C unit. It is new unit he may give you credit. $2k +$500 install - credit for old unit (le's say $500) = may not be so bad to get what you want....

zoning will be extra

Re: Shifrbv

single speed furnace, 98% efficiency

Open cell foam

10 ft ceilings with, 12 ft in living

HVAC sub said $3500 to replace 13 SEER with 16 SEER, outside coil only

I actaully hav ezero confidence that anyone involved in the house constructing knew what they were doing. My builder tried to convince me that the 98% efficient furnace meant I was going to have great cooling bills. The HVAC sub told me he never installs 13 Seer units in his new homes. I asked why did he do it in this case? No answer...

I live in North Texas, 2-3 months heat, 2 months nothing, 7-8 months cooling.

can you get together with builder & hvac company
owner?
ask why the minimum seer a/c & high end afue
furnace in a cooling climate?
this obviously is an error.

have you paid in full hvac & builder?

I'm pretty easygoing, but this isn't something
I'd accept. it will cost you more every month
until replaced. not to mention losing the 2 stage
cooling & zoned system.

what would the legal stand point be?
any contract stating efficiency of hvac system?

best of luck.