The Los Angeles area can get fairly hot. I recommend the attic insulation be at least R30. The cost of the materials to increase the insulation level is small if you are doing the insulation yourself.

What are your gas and electric rates? Gas prices are low but electric rates continue to rise. It is more economical to heat the house with a gas furnace with an electric heat pump. This is something to consider.

What size area does the heat pump quote cover? Did you review the manual J calculation? The heat pump you quoted (25VNA060) is a Carrier Greenspeed. This is Carrier's best heat pump and most expensive. It is designed to work down to very low winter temperatures. If you decide to go with a heat pump, then it is overkill for your winter climate. Carrier has other models that are less money and would be more appropriate for your location.

I agree you should invest in upgrading the windows and insulation first. The solar panels are a good idea but aware they can only generate 8KW for only a few hours a day if they are positioned at the optimal angle and orientation.

Your winter design temperature is only 45 degrees. You will not save much on heating using the heat pump with a solar panel because your heating demand is low. You should review all the numbers before you make a final decision and investment.

For a home this size, you should have two systems .Obviously this solar component is important but I don't think it should be the driving decision whether nat gas furnace/AC versus a straight high eff HP system. Cost of fuel electric and nat gas plus the solar component needs thoughtful analysis. California electric rates scare me.

What is your cost/therm for nat gas and cost/KWH for electric? You should know this.

Obviously you need a plan to upgrade your windows and attic insulation.

You refer to the var speed HP condenser as a 4 ton but Mdl number indicates a 5 Ton.

I do not care for an all flex ductwork system.

IMO

Thanks for the replies!

I've got rolls of R-30 fiberglass ready to roll out, just waiting until I figure out what to do about air sealing.

The house was designed in 1910 to be comfortable in the summer without A/C, so it has deep eaves and great ventilation. Downstairs is comfortable except on the very worst days. It's only upstairs that has a heat problem in the summer. (If money were no object, sure, I'd pop for cooling right away for both floors.)

Good catch on the 5 ton vs. 4 ton unit, that was sloppy of them.

http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/53540/Keep-Your-Elbow-Rigid-A-Lesson-in-Flex-Duct-Installation agrees that at least the places where ducts bend should be metal, and the guy who came out mentioned they would be. I was disappointed to not see that spelled out in the estimate.

The past two years of energy use were:

• 2013 heating degree days: 1501
• 2013 electric, gas use: 16960 kwh / $5,235.29, 1334 therms / $1,600.88

• 2014 heating degree days: 1037
• 2014 electric, gas use: 11609 kwh / $2050.43, 948 therms / $1,259.44

Electricity use declined because a) I started paying attention and turning things off when not in use, b) I replaced about 70 (!) light bulbs with LEDs, and c) I stopped using an electric space heater.

My previous solar house had 4.5 hours of full sun on average over the year (i.e. its 8kw array generated 36 kwh/day on average). This one has slightly more shading so I'm guessing it'll get 4 kwh/kw on average, or 32 kwh/day. The price after subsidies is about $18,000, or about $720/year over 25 years. (Net metering is truly a sweet deal.)

My goal in partly switching from natural gas to solar electricity is not to save money, but rather to reduce my carbon footprint. Supposedly all new residential houses in California are supposed to be zero net energy by 2020; I wanted to see how practical that was for my historic house. I'm still figuring it out.

The Greenspeed equipment is a little confusing in that the same condenser can be configured for either 4 or 5 tons of cooling and heating. Make sure you understand the sizing and verify the model numbers.

You didn't answer the question about the area you are trying to cool. You may not even need 4 tons of cooling.

If you can sell excess electricity back to the utility, then it may make more sense financial to heat with gas. You should run the numbers to verify this.

If you can generate all your electricity with solar power, then you are reducing your carbon footprint. But if you have to buy some of your electricity, and that electricity is generated by a coal burning plant, then you may have a net increase in carbon production.

The heat pump quote is just for the upstairs, roughly 2000 square feet. (We may do the downstairs someday, too, but the upstairs is more urgent.)

I raised the question of whether 3 tons might be enough with the guy who came out to do the estimate, and he just laughed.

He did suggest zoning (a $4000 option) as a way to reduce the tonnage, as only one room needs cooling all day... but I don't know if zones are really effective, and they do add cost and complexity. (Lots of discussion on that at e.g. http://homeenergypros.lbl.gov/forum/topics/are-zoned-heatingcooling )

We cannot sell electricity energy back to the utility; we can only bank it for later use.

We recently chose the 'green power' option with ladwp, so (at least accounting-wise) our grid power is already carbon-free. That jacked up the price of grid electricity from ~17 cents/kwh to ~20 cents/kwh. That plus the falling gas prices (we're paying about 25% less per therm this year compared to last year) do tilt the economics towards natural gas... but I've got my eye on the global co2 problem, and would rather be part of the solution. Assuming I can do it without a crazy price penalty, anyway.

I'm getting an estimate from a second HVAC guy. His first guess was 5 tons (just like the old furnace), but said 4 might be ok. He just did a quick tour, counted rooms and vents, and asked me what the total square footage was... so if he does Manual J's, he must do them later in the process.

I asked both guys for a high efficiency option and a sensible option. The first guy didn't give me options; maybe this guy will listen better.