I assume you live in a moderate climate both for heating and cooling. I prefer crawl space and for a home this size, I think 2 units over one for best comfort and control. But if one system, I would want home broken out into 2 distinct and separate zones with zoning controls.

IMO

An unconditioned attic is the worst place to install HVAC equipment in my opinion. Is there a possibility of a partial basement? If there is then I recommend installing the equipment in the basement area and running the ducts through the crawl space. If that is not feasible then the crawl space needs to be tall enough to lay the furnace or air handler on its side for servicing.

If the attic is 'PROPERLY' ventilated it doesn't matter. I live, work and play in the AC capital of the WORLD. (Katy, Texas)

Given that you are in California, with a generally dry climate, I would put them in the crawlspace. The attic will get VERY hot there while the crawlspace will be much cooler. In the south and southeast, we have problems with damp crawlspaces but you should be relatively free of that.

"I prefer nice big open attic. Sorry, I am not crawling around in a crawl
space to fix nothing. (what ever you put in, is at some point in time
going to break down... plan ahead.)"

lol

This from a "PRO" that posts his contact info for anything that is near his/her location. (Something that most all forums forbid in their Terms of Service, and something most all "Pros" would not consider doing. Seemingly OK here.)

Wow!

Saltidawg,

(Thank you in advance for giving me the opportunity to explain this.)

There has to be a motivational reason for a pro to answer questions. It's a form of advertising. I have helped a few local people who have frequented this board.

This occupation requires inspection / diagnosis. All you get in a forum board atmosphere are guesses. Sometimes the guesses are right, often cases the guesses are wrong. I could pick nearly any thread on this board as an example.

Licensing is required in most jurisdictions. This field is not DIY. No manufacturer will warranty a part or equipment for DIY installations.

You don't have to like it, but I serve a purpose here. That purpose pays me back by helping folks that are local to me when they decide to hire me.

They know I am local to them: BECAUSE I TELL THEM. How else would you know?

I am a Texas Licensed HVAC contractor servicing the Katy, Texas area and some surrounding areas. 832.475.6895

I repair ALL HVAC brands, I am able to design, install, repair and modify HVAC systems. I am EPA universally certified to handle ANY refrigerant. I am NATE certified in installation and repairs. I have an AOS degree in HVAC/R Mechanic graduated with honors (Deans list thru all phases) 1996.

You can subscribe to my YouTube channel here.

It really dependa in what your plans are regarding your attick and basement. Since you are in a warm climate area I would go with the attick sincewarm air rises and it will help with your cooling. But making sure it is properly insulated is very important.

http://www.heating-repair-chicago.com

Hey Ray, I just subscribed to your YouTube channel. Good stuff, watching videos now!

Attic or crawl space is the choice? Choose the one that is sealed off from the outdoors and coupled to the living space.

Another question - What is recommended for bay area - furnace + A/C? or mini splits? mainly wondering about operating costs.

"Another question - What is recommended for bay area - furnace + A/C? or mini splits? mainly wondering about operating costs."

Depends on energy costs. Generally, in Northern CA with PG&E or SMUD electric rates, gas is way cheaper.