Long term planning - solar roof + powerwall + heatpump?

[Kipernicus]

Hi,
Our house in the Bay Area is about 20 years old, and some things may be reaching the end of typical life. Already some home insurers wouldn't take us because the roof is too old. Our furnace still works but who knows how much longer it will last. Our home doesn't have AC and it would be nice to add.

So, long term I think it makes sense to replace the roof with a Solar Roof + Powerwall.
Does it also make sense to replace the gas furnace with a heat pump that does double duty of heat and cooling?
I figure that without solar, it may be better to use gas for heating but with solar, that changes the equation right?

Thanks

 

[Tam]

...So, long term I think it makes sense...

I think in a long term your plan is very good. You pay Solar, Battery, Heatpump once upfront and you don't have to worry about operating costs any more.

Of course, if you want to heat with gas so you don't have to pay an expensive upfront solar, that would be fine too but you still have a monthly gas bill as opposed to pay your solar once and forget about monthly bill!

 

[ItsNotAboutTheMoney]

Plus insulate. Insulation cuts heating and cooling energy requirements. If you're thinking heat pump and have tiered rates, the negawatts could give good marginal savings.

 

[abasile]

For many homeowners, improving the insulation and overall home envelope would be the best place to start. With a twenty year old home, though, you probably already have at least R-13 insulation in the walls and double pane windows.

In terms of the lifetime of a gas furnace, twenty years does not seem like a long time. Further, your climate is quite moderate, so the heater probably doesn't need to be used a great deal (unless perhaps your home isn't sealed well enough). One possible alternative to replacing the central heater could be to leave it in place, and add a heat pump based ductless system for selected rooms.

Presently, we have solar, a 92% efficient gas furnace, no air conditioning, and two Powerwalls on order. We don't need AC for the entire house thanks to our cool mountain location, but it would be nice to have AC for a few weeks per year in the central area of our home. I'd also like to reduce our consumption of natural gas, a fossil fuel. Our tentative plan is to add a heat pump with a single air handler (18,000 BTU) for our central living space. This could be supplemented with part time use of a couple of space heaters in smaller rooms, thus substantially reducing our need for the central heater.

Also, an advantage of keeping a gas heater is that it can be used during power outages, drawing on the Powerwall(s) only to start it and run the fan.

 

[miimura]

You use hot water all year round, so a heat pump water heater makes more sense to me if you want to move something off gas.

 

[shs1]

In the summer one cool thing about a geothermal heat pump is that you can use the heat generated from cooling the house (air conditioning) to heat your domestic hot water for showers, laundry, etc.

 

[miimura]

In the summer one cool thing about a geothermal heat pump is that you can use the heat generated from cooling the house (air conditioning) to heat your domestic hot water for showers, laundry, etc.

Conversely, if you have a heat pump water heater near your solar string inverters in a somewhat enclosed space, it will pump the heat rejected by the inverter(s) to the water, increasing the water heating efficiency and cooling the inverters.

 

[ecarfan]

Does it also make sense to replace the gas furnace with a heat pump that does double duty of heat and cooling?

I live a few miles from you in a house built in 1959 with a radiant heat system driven by a gas boiler (which is relatively new and was the best available when purchased 15 years ago). I have often wondered the same thing. Long term I would like to get off gas entirely, expand my 9.8kW solar system, add another Powerwall, and have a heat pump powered by my own electricity.

 

[shs1]

How one produces or pumps heat and how it is distributed around the house are two different things (obviously). In our case we have a solar powered WaterFurnace heat pump that takes (or puts) heat from one of our ponds to heat (or cool) the house. We have a complete air circulation system for AC and can heat the air as well with this unit, but typically distribute the heat around the house using radiant heating that uses pex tubing in Warmboard for fast and even heat distribution under our hardwood floors. The water for radiant heating is heated as it passes through a heat exchanger in one of our domestic water tanks. The system is very efficient and convenient and allows separate and fairly fast temperature control in our various rooms. Solar/geothermal/radiant/warmboard is a great combo. Now I just need my Powerwall 2 installed in a way that will work with my generator!

 

[Spectre]

We think the same I believe, anytime something comes to my attention I step back and look at the whole picture. So usually I end up liking the forklift upgrade model, slam it all in. PG&E and the State have some cheap loans and incentives for home energy upgrades. You could probably roll up allot upgrades.

For me not everything must make finite economic sense. Comfort, lifestyle and being an energy hobbyist in me win out.

 

[SSedan]

Just to tell you something about the effectiveness of modern heat pumps, last December we switched from baseboard electric and a garbage high velocity AC system to Fujitsu minisplits 2 outdoor units each powering 3 wall units, 2400sq. ft. 40yo leaky Bi-Level near Green Bay so an average year will see -15 to 90degrees(-25 to 102 at the extremes), electric budget was down 20% before I went and bought my P85 and the house is more comfortable all the time. I think had I not thrown the numbers out of wack with an electric car we would have seen a 25-30% savings had I gone a full year. Bathrooms and laundry room are still on baseboard electric.

I think I need to supplement with gas, probably by converting a decorative wood fireplace to gas, but would only intend to use it in sub-zero temps which we see a fair amount of, but the heat pumps did get the job done even if they did work hard to do it last winter. Considering changing my 22yo electric water heater to a hybrid since the heat pumps work so well for the home heating.