those heaters are great , but have drawbacks . 1 they do require pressure adjustments , from summer to winter as pressure changes due to temperature outside , if the pressure is too high , the water won't heat , too low and the unit will overheat and flow will diminish , kinda like a ferrari , definitly isn't turnkey . these are really popular in europe , been around for decades , we are finally catching up , but we americanized it and decided that 1 should be fine , but in europe they do it properly , 2-3 per house , they are smaller and simply provide the hot water for a specific source , like the unit in the bathroom has a higher out ( for showers etc ) at the kitchen it can be a smaller unit , generally hot water for cooking and washing dishes. Now also if you are using natural gas to run the tankless , you have to think about how many btu's the imput is . you need to see what your total " on " usage is , cause if you have a furnace , gas fireplace , cooktop , and the tankless ( which are a gas glutton 80k-150k btu imput ) your current gas meter and fuel line may not be able to keep up . generally the trouble happends when the furnace fires off when the tankless is heating water one suffers . my company now requires customers installing these units ( to avoid us being blamed for pressure problems ) is to upgrade their gas service and gas meter , to handle the load added to it . typically a 1/2" gas service , providing 7inches of water column delivery to the house can give you 275,000 btu's an hour so once your tankless kicks in , theres not enough volume or pressure to run anything else .