While the case for tankless water heaters might sound like a no brainer, there are several reasons why going this route might not be for you.
Limited Output
A big tank water heater that stores 40 to 60 gallons of hot water at a time will keep your showers, laundry, and other hot water needs properly satisfied for quite some time. Modern tanks reheat additional supply quite quickly as well, so you'll quite likely never run out of hot water when you need it. A tankless water heater has a throughout limit, able to supply a few gallons of hot water at all times but also at a time. So if you have a large family and everyone's taking a shower, doing the laundry and dishes at the same time, a tankless water heater might not be up to the task or suitable for your family's particular needs.
Additional Cost
While a typical tank water heater might be as cheap as $300-$400, they can price out up to $1,000 depending on options. But if you consider a tankless water heater probably starts closer to $1,000, you've got a pretty big difference in price tag. Of course, the idea is to make up for that extra cost as you use less energy along the way, but still, having to put up that money up front isn't always an option for everyone.
Instantaneous Energy Requirement
A traditional gas water heater might use 3o,000 to 50,000 BTU of natural gas or propane while it's heating up your water. A tankless water heater might require perhaps 150,000 to 200,000 BTU to do the same as it heats up your water on demand. Sometimes this high BTU requirement isn't possible, as I found out myself during my own home renovation, where there's a low pressure main, so we're limited to a fairly low total BTU spread among all of our gas appliances. If you consider switching to electric instead of gas, you'll need to be sure that your electrical system is up to the task. The price of electricity is usually higher than natural gas in many areas too, so you'll need to consider the cost of energy as well.
you plan on installing double showers with bells and whistles? you wil run out of hot water.
also, the maintaince onn them is pita.
others might have opinions, I have a rennai. tankless, right next to a 50 gallon w/h. the tankless is turned off.
