you will have to ask the companies if they will do a load calc, not just expect it to be offered.
some companies will charge, but offset the cost by subtracting it from the install.
all companies will hold the load calc until you sign..so you won't take their work & shop it to different companies.

some homeowners hire an independent for calc & use the calcs to shop companies...which as you own the calcs you can do.

it is normal for homeowners to not know to ask for the calcs...for some hvac companies.

I'm far far away...so no company recommendations from me. but you could go to hvac-talk.com & ask for pro members in your location.

best of luck

Your compliant is very common. It seems few HVAC contractors want purchase the software and devote the hour it takes to perform a proper load calculation.

The alternative is the use the size of the current equipment as a guide. If the current AC was able to maintain the set temperature, did not short cycle, and maintained humidity below 50% then it was properly sized.

What size do you have currently and what sizes are you being quoted?

So far all except one contractor has said 3 ton, only one said 2.5 ton. The one that said 2.5 is not from the specific area I live in, the others are so they know it gets to 110 here....the current system is a 15 yr old 3 ton, does not short cycle and on the really hot days can not get the house below 78-79 even when asked to (don't have much humidity and no way to monitor it)....I have 3 more contractors coming this week and next....will be interesting to see what they say.

First of all, you don't size to the extremes.

The problem with getting a load calc is universal throughout the country.

There are some states that actually mandate a written load calc prior to sale, very few though.

I understand homeowners who find it difficult to get a load calc performed. Take the initiative. Do one yourself. And then insist on getting one performed by your installing dealer as a condition of the sale. Then compare the two.

I can provide you a load calc link if you would like.

IMO

A 3 ton condenser should be sufficient for a 1075 sq. ft. house. HVAC contractors tend to over size equipment. The 2.5 ton size may work, but it is hard to tell without knowing the details of you house insulation and window orientation.

Is your concern you will be over sized or under sized? I would not go larger than 3 tons. These guys want to go by their experience in similar houses in your area. It is not the best method, but it does have some validity.

If there is no load calculation then have the contractor put in writing what he is prepared to do if the size is not correct.

What was the size of the old unit? Did it heat and cool your home satisfactorily?

The size of the current unit is 3 ton and on most days it does ok, on 110 degree days it does not cool below 78-79 so that is not good enough to me. My concern is 3 ton could be too large from what I have read here....I have dual pane windows but insulation in the attic is barely up to par noted by one contractor. Heating was fine with the 3ton. I questioned the first contractor on the size and he said he has clients in my area who have similar sized house with 2.5 ton and they do not get sufficient cooling. I have a large window facing west in direct sun from 1pm on...I need to get a solar shade for it but significant heat comes in that window. I close the blinds but they are inside so heat still comes in....the window is like 6 x 8 feet. The current 3 ton hardly ever shuts off on days over 90 degrees.

The idea that a 3 ton AC condenser can not keep up at 90 degrees in a 1100 sq ft home strongly suggests the attic insulation problem.

BTW, where is ductwork located?

Keep in mind if you go up in size above 3 ton, you will need to go up in size on your furnace as well which most likely is already oversized. That would be compounding a problem.

IMO

This post was edited by tigerdunes on Thu, Sep 12, 13 at 11:26

the ducting is in the attic :)....no one has suggested going above 3 ton. All but one are saying 3 ton is the one to go with. And so now I know ya all will say to deal with the attic but we can not afford to have the system put in. deal with the asbestos ducting AND have the attic insulated further....uggg. The system and ducting situation is going to tap us out for now.

The duct system being in the attic could be a major factor...

Some easy simple ways for anyone to check the performance of their air-conditioning system

Try to check the run time and off times of the air-conditioning system and write down the outdoor temperature; it's best to do this on the hottest days and even when the humidity is at its highest.

Let's say the air conditioner runs for 15 minutes, then off for 15 minutes before it restarts, that's a total of 30 minutes for complete cycle so you take 15 minutes and divided by 30 minutes and you get .5 or 50% runtime; will say I have 2 ton air conditioner but due to ductwork and other factors that will not deliver even 23,000 BTU per hour instead figure 90% of 23,000 and multiply that figure is 20,700-Btuh by * .5 that is only 10,350-Btu used per hour.

That formula can be used for any complete time span cycle.

Another formula is the EER or energy efficiency ratio formula; the BTU per hour divided by the wattage used. Another way to use the formula is to take the BTU/hr and divided by the units EER rating.

Let's say the air conditioner as a nominal rating of 23,000 BTU per hour divided by a 9.5 EER that is 2,421 Watts of power used.

A technician can then taken amp probe and multiply the amps times the checked voltage which will equal Watts the unit is actually drawing. From that reading you can figure what its actual EER is.

Another way to verify what the load is, is to do a load Calc; I'll provide you with the free online load Calc with which you can experiment with until you get a proper load Calc performed, which you will then have to print out because you cannot save your load Calc's.

Then go outside and take the temperature of the discharge air and subtract the outdoor temperature from it.

On a 10 and 12 seer condenser the indoor split at 50% relative humidity and 80ðF will should be around 19 to 22ðF. The outdoor condenser split should also be between 19 and 22ðF.

Here is a link that might be useful: Free online Whole House Load-Calc

Do you have performance issues for all rooms on hot days or is it just certain areas?