I think the first thing to do while looking for an inverter, especially for a boiler, with pumps and fans (induction motors), the need of a Pure sine wave inverter is a must. It's more expensive, but I think it's the way to go. I do not have a boiler yet. But I've been reading and getting educated on basic back-up system with grid-tie in inverter and renewable, I am looking at a minimum of 3000 watts that could feed the basic (Frdige, freezer, Boiler fans, pumps, controllers, camputers, a few lights and tv). As far as water goes, i have a surface well and I am planning on installing a cheap 12v pump (RV style, self priming, pressure control) to have water at home. Xantrex is a big company with a lot of inverter possibility , but I"ve heard (Reading through diffrent forums) that with the time there overall quality and costumers service is getting really poor. Xantrex are making some 240 units. I think a lot of the xantrex units are not servicable. Sunny Island is a US based company with (I think) manufacturing in the US, seems like a top of the line units with a good servicable product and great costumer service. Outback are making some good unit too with a lot of possiblity ( I think you can stack them for more power and 240). IT all depend on where you want to go and what you want to do. There is some charger / inverter. A bigger charger good be a great plus in a extended outage if you want to charge de system while the genny is running and beign sure your batteries are top out within a few hour, wich won't happen with a trickle charger. As far as battery goes, sometime you can get ''used'' batteries for cheap that are still good for a back up system .