All Margin Cook Stoves and Heaters are airtight. With the new generation of wood burning, airtight cook stoves and heaters, a bed of ash is formed to nest the hot coals and increase efficiency. They will keep a controlled fire all night to heat your home even on the coldest nights. Not only do these stoves provide a great source of alternative heat, they can also be plumbed directly into your home's water system to provide an alternative fuel source to heat your hot water. Hydro, however; is not required to operate any Margin product. All Margin stoves and heaters come with a One-Year Manufacturer's Warranty Plan.