You are paying for it. I wouldn't wait for the walk through. Stop it NOW.

bamachem, I had no idea you were a Purple Elephant. My BIL is one too. In FL

You may be alright if you have plenty of shade. There are 3 guys at work that built new houses that have about 650-700 sq.ft. per ton of cooling. They complain when their units run constantly on hot days to maintain 78° even though the t-stat is set on 72°. They do eventually drop to 72° after the sun goes down. I tried to warn them. My units (500 sq.ft./ton) cycle on/off and maintain 71°-72° even on 100+ days with ZERO mold issues.
Good luck

well take some advice from a guy who is feeling the pain right now,, go with a bigger unit,, at least a 4 ton (if not 5). Without know the factors in your home (ceiling height, windows, east/west setting, shade trees & etc.). As my earlier post stated, we have roughly 2500 sqft home down stairs with a 4 ton unit currently and it just can't cut it! Of course we have an upstairs loft and 20 ft ceilings, house sits east/west and the entire back of our house is windows in the middle of a field! the 4 ton gets it close, but it's just not quit close enough. The humidity in our house is great (stays around 35%), but on days like today it just can't cool my house below 76 degrees and that's with no movement or activity in the house! Once we get home, start moving around, running lights, electronics, cooking and such the temp will go up another couple degrees which makes it uncomfortable along with the fact that the unit runs non stop. While bldg go ahead and go with a 15-16 seer unit and get at least a 4 ton if not higher depending on your home design and settings. that's my 2 cents.

HC

Yes, Really.

So, he should trust a forum with open access and listen to advise from people designing systems in Wisconsin, Montana, and the rest of the country? Wow.

I understand exactly what Manual N is - glad you do too. I also understand what a load calc is since I do them for a living. I hold 6 HVACR unlimited state licenses, not just Alabama, plus my PE. I am a regional chairman of ASHRAE (American Society of Heating, Refrigeration, and Air Conditioning Engineers). I'm not obilivious to the design criteria and steps. The sqft/TR method is a rule of thumb and is used to "check" the final calculation. It is NOT used to perform the calculation, but if you do the calculation right, then you'll be in the ballpark. For ~80% of the country, 750 sqft/tr is fine. For another ~10% of the country, 650 is good. For the southern coastal areas (SC/GA/FL/AL/MS/LA/TX) that simply won't cut it as it's not adequate to address our high humiditly loads (laten heat load) as well as the sensible heat load (radiant heat load).

When you oversize a unit in a LESS HUMID climate, you likely will not see as much of a load on the system since it doesn't have much dehumidification load. Since there is very little dehumidification taking place, then the system will run a very short time and not properly cycle the air in the home. THAT will lead to excessive humidity in certain areas which can be conducive to mold growth.


Now, back to the original post...

In Mobile and most of the Southeast, we have just the opposite problem. We not only have a high solar/radiant load, but an extremely high humidity load as well. When you condense just 1.5-gallons of water in one hour, you consume roughly 1-Ton of capacity. A home AC unit will typically do that in Alabama with no problem what-so-ever. A home that is very well sealed (vapor barrier) and using high-efficiency windows and doors plus extra insulation will still produce a LOT of water off the coil when running because it's a factor of humidity and infiltration along with the amount of makeup air and not how much insulation you have.

Lets say the inlet air is 75F with a dew point of 65F and an average coil temperature of 45F and a desired discharge air temp of 50F-55F. What happens when you cool air in a home is the first heat the coil removes is the sensible heat. That means you can measure the change with a thermometer. You drop the air from 75F to 65F and it takes very little capacity to do it. As soon as the air drops to 65F, you start to condense the water from the air. Condensing water on the coil will cause zero change in air temperature but will require a lot of refrigeration capacity. To drop every degree of air temperature, the system must ALSO remove the associated water content at that particular dewpoint as the air travels across the surface of the coil fins. You will contine to condense the water from the air until it leaves the coil at around 52F - but only when the system is properly sized for the conditions. The forming of condensation from the air is the primary load to the system - and can be in the order of 80+% of the load depending on conditions.

If you do not design for a high-humidity load with decent make-up air and infiltration, then you will not be able to get the air down to the temperature that you want, the relative humidity will be higher in the home, and you simply will not be as comfortable.

Lastly, if they give you a load calculation sheet to show you that they're right about the sizing, how will you know they're right? Will you get someone qualified to check the calculation or will you just trust them? What happens if you just trust them and they're wrong - either intentionally to keep the price down or by a mistake? Do you really think they'll come replace the indoor and outdoor units, possibly the copper, and a lot of the duct out of the kindness of their hearts because you're not "comfortable" or do you think they'll tell you to stick it up your rear because they have a load sheet that they used and you saw/approved and you should have told them if you thought it was too small before they got it installed?

Bamachem, are companies required to do a load calculation before selling/installing units in new or existing homes?

He shouldn't listen to anyone behind a computer. You accuse the A/C guy of ripping him off without knowing anything about him or the situation. I admit I have never installed a system or ran a load calc for anyone on the coast. I do know you can get in trouble by sizing per sq ft no matter where it is. I have installed systems that calculated to 750 sq ft per ton and have been operating for over 7 years and the customer is happy. We have also installed where the demand was 400 sq ft per ton. Point is every house is different and NO one can tell him what he needs over the internet. I enjoy this site but this is the reason I rarely post. Some people try and get into a pissing contest about everything.

Just a slight digression -

Shouldn't all of this have been decided before starting construction? I know that is what we did so we would know what the cost of the house was going to be. I guess different builders do things differently or maybe this is not a "custom"-built house.

Exactly... Just like this...



He is paying for a home that is well-built with an AC system adequately designed for his area and conditions. 714 sqft/TR is very unlikely to be satisfactory unless he is building an EnergyStar/LEED home, which is even more unlikely.

What is much more likely is that they are taking short-cuts on the AC system since it is the single most expensive appliance in the home in order to save on their overall installed costs and put more profit in their pockets. Now THAT is not uncommon.

No, he shouldn't listen to anyone, including you, for a definitive answer over the internet. He needs to take that load calc and a set of plans and some pics of the lot/build to someone else for a second opinion, which is sound advise to follow. He should plan to pay them for their time to do the calculation, and then he should take their calc to his builder and sort out the differences. He should make sure that the HVAC work stops until the other calc has been performed because every day it goes on is going to cost him twice as much later to rip it out and replace it if it's wrong.

He should NOT just take their word that the system is adequately sized since the sqft/TR is outside the "norm" for this area.

Yes, then double checked when the roofing is on and studded in. Just to be sure they have an exact estimate.

Mine is 1 level, 3200 sq, elevated ceiling and windows everywhere. Have had no real problems with cooling. It runs all the time as we have little shade and like the house cold. I turn it up to 73 during the day and 70-68 at night.

BUT the system does not have a problem maintaining the temps I set. May get 1 or two degrees over 73 on a REALLY hot humid day.

http://www.hvac.alabama.gov/pdfs/AdmRulesAug09.pdf

Are they required to do the calculation? No. Are they required to adhere to the MINIMUM standards set forth by Manual N/J? Yes. In other words, the law does not say specifically that they have to do a detailed calculation, but they must meet the minimum requiremenst set forth by one.

Hey guys...thanks for all the replies. For the record, I am having a Breland Home built, so I did not get a choice on things such as the A/C unit, etc. It comes with what they install. I talked with the builder today with my concerns and they had the A/C company call me to clarify. They said that they did not specifically do a load calc on MY house, but have done about 9 or 10 of the same house in the past based upon an initial load calc and that ALL customers were satisfied. The house is well built, low e windows, brick exterior, but little shade on the property. 10 ft ceilings throughout (or maybe 9....), vaulted in the family room.

I guess I'll just have to wait and see, eh?

Since they have 9 or 10 the same way, providing you with 5 references for you to call shouldn't be a problem then....

You've done all you can. He'll find out soon enough. Next summer when he complains the builder is gonna tell him, 'you've been in the house a year. Too late'

Bama......why did everybody get away from electric a/c's (don't know proper name)? Parents house has gas heat, electric a/c, (non-heat pump). They have NO cooling issues, and always a lower power bill than me......I have better insulation, windows,ect.....

I joined this forum simply to suggest that you stick with what you know.

The HVAC industry is plagued with over sized equipment married to undersized duct work. The "bigger is better" routine doesn't work for HVAC.

Ummm, yeah. Signing up just to post this. I'm sure your opinion will carry LOTS of weight....

I think what you're asking is why did people switch from using an AC unit with gas-fired heat (or electric heat) to using heat pumps, right?

Well, it's more energy efficient to run the HVAC system in a "reverse cycle" of sorts to produce heat for the home than to fire off electric strip heating. It's also typically cheaper to heat with a heat pump than using a gas-fired furnace.

The AC cooling cycle is essentially the same on the systems. The difference in power bill is most likely due to the type of refrigerant and build of the houses than the type of unit.

Screw the load calc - demand a bigger unit. If your the one who put down a deposit and the builder is building YOUR house then YOU ARE THE BOSS! If you let them walk over you, they will.

My two cents (which ain't even worth that).


Edited portion below...


= getting screwed and regretting it next summer.

Demand a 5ton. Don't wait do it now...

Bamachem is dead on 500sq per ton is standard practice in Al hvac

Mine is sized at 454 sq.ft. per ton. Foam insulation throughout with Energy Star doors & windows. Sealed to the max.

It's the perfect size and never costs over $.06 per sq.ft. per month to heat or cool.

I would also suggest a 4" filter in addition to the 1" return grill filter, but I guess that's totally out of the question?