Hello solargary, Thanks for that counterpoint. The reason why I'm not 100% sure about solar water heating to heat the water used for a radiant heat system is because of the weather. (I want to like solar water heating but I'm not sure...) Generally speaking, the west side of San Francisco needs heat the most in Nov, Dec, Jan, and Feb. During these months, I see the least amount of sunshine (as verified by the PVWatts calculator). Often times, we see very little direct sunshine during these months as it is raining. During these conditions, I don't think I'd be generating any heat with solar heat collectors (I'm guessing - I have no direct experience with solar heat collectors - I'd love to be proven wrong). Consequently, I might be in a position where I need hot solar water to use in my heating system the most during the time that I don't have it. However, given that there is *light*, I could certainly be making electricity, hence my query on a electric tankless water heaters. While the PVwatts link shows that a DC 5KW PV system generates 420 KWh AC electricity a month in mid winter, it also shows the over the course of the year, it could generate about 600 KWh per month. The beauty of a grid-tie system is then (I'm assuming) is that the utility company calculates your balance on a yearly basis - so the energy deficit that I'm have in the winter (since lights, computers, etc would eat up most if not all of that 420 KWh) would be balanced by an energy surplus in the warmer months (where I could be generating around 710 KWh per month) The issue with gas tankless water heat for the radiant heat for me is venting. I need to figure out a way to vent the water heater - I live in a rowhouse so its not easy to find a hole on the exterior surface. I'd probably have to vent the thing on the roof .... which would make it difficult for me to place the unit 2 or 3 stories below the roof. An issue with solar water heat for the radiant heat system for me is finding the room to store all that heat - I would be extremely hard pressed to find space for a 200 gallon tank or even a 100 gallon tank for that matter. Actually, I *could* find the space - but that would be 3 stories down from the roof - which would then make it difficult to vent a gas fired heater.... So many constraints.... Thanks

theblaiser While probably not telling you anything you don't already know, you have two of the most expensive forms of fuel for winter heating. I am attaching a fuel comparison calculator which will give you a close estimate. You will need the efficiency on your LP gas stove/inserts. Of course the baseboard electric heat has no efficiency. Just plug in the electric cost and the calculator will spit out a cost for baseboard heat. It appears LP is more expensive using an average electric cost of $.115/kw. A high eff heat pump would save you some significant $$$. Hope this is helpful. IMO Here is a link that might be useful: Fuel Comparison Calculator

I'll post a calculator I found below, but based on the figures you posted, it would cost $31 per million btus for electric resistance heating ( your electric furnace option), $15.50 for the same amount of heat using a heat pump, or $10.50 for natural gas. The wrinkle with using natural gas is that to fully take advantage of the available savings, you would want a gas water heater, clothes dryer, and probably a gas stove - The water heater would require a chimney, and buying a houseful of appliances doesn't sound like an option for you - keep in mind, all of those appliances would require gas pipe inside the house as well, which wouldn't be included in your $850 cost to get the gas to the house. Plus, you would likely incur permit and inspection fees for a changeover. Based on what you've posted, In your situation, I'd probably get a top-shelf heat pump for heating and cooling the house, and possibly a heat-pump water heater as well. I've posted a link below so you can run your own numbers Here is a link that might be useful: energy cost comparator - requires microsoft excel

Tesla Powerwall is a bit different as it uses batteries made with Lithium, however the base model will at best give you only a few hours of run time. Costs $5,500 of which doesn't include installation costs, taxes, fees, permits etc. Tesla Powerwall For that 'maintenance free' solution you will most likely be forced to replace the powerwall every 10 years, maybe less than that as if your system loses capacity leaving you in the dark your choices will be few. So to do some rough math to be possibly free of the electric grid... let's say you can depend on 12 hours of full sun everyday. (of which we know is not possible) So you would need a battery system to deliver the other 12 hours of power. Lets say the base pack works for 2 hours. So you would need 6 times this amount. 5500 X 6 = $33,000! This doesn't include installation, fees no solar panels etc. to make matters worse you spend this every 10 years or less. ( nothing is free --- if you don't spend it on maintenance you spend it in dollars.) For comparison: Your power usage at 1500 kwh's per month at $0.21 per KWH is $315 x 12 = 3780.00 x 10 years is 37800.00 from the grid cost. Just realize solar array prices were not included in above powerwall costs. I believe by the time you figure installation costs for the powerwall, it would be cheaper to just remain on the grid. This is why battery backup is only used for power critical uses. The cost doesn't justify the means.