Location?

How would you describe in the insulation properties of your home?

What size system are you replacing?

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IMO

Location is in San Diego, and the insulation is probably pretty minimal. Most of the windows have been upgraded/replaced, but we still have a few to go (meaning that they're the old school, crappy kind so popular in the 80s. Our existing furnace (30 years old) is original to the house, and apparently it's a 5 ton. And we've been told it was way too big for the house.

Weather-wise, for about 5 months of the year, we don't have to run either heat or a/c. We would probably turn the a/c on beginning in late July/early August, and use it off and on through late October. Not a lot, but when it get hot here, it gets really hot, and the indoor temps can reach 90 degrees by late afternoon. Heating-wise, we probably turn the heat on in mid to late November, and keep it on until February/March.

Fwiw, right now, in the middle of the afternoon, it's a comfy 75 degrees both outside and inside, and won't heat up much more than that until we start to get our heat spells in August.

What size home do you have?

Is humidity a concern in the summer for AC cooling?

Size of existing furnace?

And finally,describe your typical winters.

Post back.

IMO

I lived in San Diego years ago. It is VERY location driven there as to A/C needs.
where I lived - Del Cerro area - we needed A/C maybe 5-7 days a year and heating maybe the same. Twenty miles away in Chula Vista area, needed A/C much of the summer.

Where are you?

A would think a 1900 sq. ft. house in your climate would do fine with a 3 ton AC.

Has either contractor done a heating/cooling load calculation? The proper way to do it is to enter all house dimensions, insulation values , and temperatures for your climate into a software program. The result is the heating and cooling requirements during typical summer highs and winter lows. This is known in the industry as a Manual J calculation.

See if you can find a third contractor who will do a calculation. You can do your own calculation for $50. It is not the same software as the professionals use, but it is a good approximation.

You need a load calc. I would think no lower than a 3 1/2 ton but only a load calc would confirm.

IMO

I'm not sure if either did a load calc. I know they grabbed a laptop and did a few things, but I just thought they were pulling up some other info. They might have done a load calc since both spent about 20-30 minutes (estimation) checking out the garage and the attic. Salti, we're in San Marcos but I'd say our weather patterns are closer to coastal than inland. We don't stay as cool or cloudy as it does in Encinitas, but we're always cooler than, say, Escondido or Chula Vista.

Tiger, our house is around 1900 sf, and humidity in the summer is usually around 65-70% and it feels quite comfortable, although we get the occasional hot and humid spells when the storms come up from Baja and it gets really muggy. We also get very, very, hot and dry spells when the humidity plunges to 25%. But with the weird global weather we've been seeing this year so far, who knows, we might get more humidity this summer. Usually we have dry, desert heat when it gets hot.

Winters are quite mild. Daytime temps rarely float below 65, although we get maybe 10 days a year when we see rainy days in the high 50s. Nights at the coldest part of winter hover in the low 40s and very high 30s. Humidity is generally around 60% when it's chilly.

Call dealers and ask if they performed a load calculation when sizing AC. If they did, ask to get a copy in writing.

IMO