I have a oil hot water system in my home. A pellet boiler dealer told me that they can install a boiler and use my existing oil system as a backup. This would be done by disconnecting the water into the oil burner and connecting it to the pellet boiler. Then taking the out from the pellet boiler and connecting it to the in on the existing oil burner. This is done so the oil will only run if the the pellet boiler was not operating. I currently don't have a hot water tank the oil burner runs all year for hot water. He didn't mention any hot water storage tank for the pellet boiler.