re: How many tons of AC for a home with spray foam insulation?

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definitely don’t know any of that. Who can do this manual j? Pretty much any hvac contractor?

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If you already live in the house you can figure this out yourself. Your system should be able to maintain 75F up to the 99% design temp for your area. This is typically 100-105F for the southern areas of the USA.

When your area hits the design temp, it should hold 75F while running 90-100% of the time. If your system has a duty cycle less than 90%, you are oversized. If your system is running 100% and the temp goes above 75F, you are undersized.

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500 square feet = 1 ton

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So that's what everyone is saying is kind of obsolete now depending on a ton of factors specific to the house.

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Yep. Ceiling height being a big one. That rule of thumb assumes standard heights.

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So my ceilings are 10 ft which is higher than standard but the place is supposed to be significantly more energy efficient than a standard home.

OP, if this was done on a new build purchase you are likely fine. I wouldn't sweat it too much.

The concern with spray foam is that due to it being efficient the HVAC system doesn't run enough and remove enough of the moisture. There are other cheaper methods such as ceiling fans and dehumidifiers that can be used to accomplish that also.

The most important thing for an AC is to be able to cool the house. I'd ask the builder to prove it. It won't cost him anything likely to get his HVAC subcontractor out there or pay someone a little to do it, he should have done this already anyway.

More than likely, as said the 500 sq ft is for older less efficient homes and you are fine.

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More than likely, as said the 500 sq ft is for older less efficient homes and you are fine.

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Thanks. The builder says that a manual J was done and he's going to get a copy. I feel a good bit better about this after hearing from y'all.

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Thanks. The builder says that a manual J was done and he's going to get a copy. I feel a good bit better about this after hearing from y'all.

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Sounds like you have a quality builder. Having properly sized equipment is rare these days. Most crappy builders throw oversized equipment in houses and dont care that it decreases efficiency (higher utility bills), decreases comfort (less humidity control) and shortens equipment life. The extra start/stop cycles on oversized equipment shortens the life of the equipment as most wear and tear occurs during starting, not while running.

Then on top of all that, when you have properly sized equipment, you'll likely buy properly sized replacement equipment in the future instead of wasting money on larger systems that you don't need. That saves even more money.

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Really sounds like this country is wasting a ton of energy on oversized HVAC equipment

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In the residential world for sure.

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Is it unusual to have 3 ton coil/air handler and 2 ton condenser. I've read online that that can cause problems with humidity and with a tight spray foam house, perhaps it could be exacerbated?

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This is a complicated question. It depends on where you are located geographically. The interior coil is often oversized by HVAC installers to get a higher SEER rating out of a system. So putting a 3ton coil with a 2 ton AC can get you higher SEER ratings IF the system (coil and AC) is AHRI listed/tested to do so.

The issue with doing this is the larger coil has a larger surface area. This is great for getting the most heat transfer into the refrigerant. the problem is this makes the refrigerant warmer. As a result, the temperature of the coil will be warmer. The downside of this is that it reduces the capability of the coil to remove moisture/humidity from the air. The cooler the coil temp, the more humidity it can remove.

In a humid climate where comfort is the primary concern, you would probably want a 2 ton coil matched to a 2 ton AC unit as that will be better at latent cooling (removing water from the air).

If your system is sophisticated enough, you can still get good humidity control out of a 3 ton coil. If the Air handling unit (AHU) has a variable speed ECM blower and the proper thermostat, the thermostat can be set to slow the blower down when the humidity is high. The slower CFMs across the coil allow the coil temperature to go down and this pull more water out.

If you have detailed equipment info (model numbers and such) I can help you dig into this a bit.

So far I have only gathered that the condensers are American Standard 2 ton and Air Handlers are Lennox 3 ton.

Damn.. I'm asking the builder about this certificate. What do you recommend I do? Sounds like I need to get someone else out to evaluate it.