I need to know what size tankless water heater I will need to connect to washing machine. This is the only appliance the tank will heat. Can I use a 2.5 gallon tankless?
Thanks

How carefully have you looked at the numbers on this? Even a 2 1/2 gallon one is fairly expensive. How much water does it take to fill your washer? Would a small 5-10 gallon tank provide enough to fill the washer and recover in time for the next load? I don't think the tankless heaters live up to their hype. Those here making their living selling them and installing them don't like me suggesting people get the facts before buying one.

The idea of a tankless water heater is great, it works wonders on commercial steam cleaning or hot water pressure washers.

But the trouble they have there has always been the intake water volume and pressure, They have automatic shutoffs and safety if there is not enough, and many homes, even at the intake main does not have enough of either to operate them. And where you do at the intake, often at the point where you use it, you don't, And if you are only turnng the hot water on a little, often it is just not enough to make the unit kick in.

* I am sure they are working on this on the home units but I know that the requirements for the commercial equipment we worked with a few years ago, were very specific or they would not work.

Next of course you have to have clearance for them ( which means space)

So the issues of how many washer fills you use a day, how much water per load. And why in heavens name are you using a lot of hot water for a clothes washer unless this is a commecial laundry doing white linens all day. Most clothes are cold water washed anyway now adays. But that is another issue