Why don't we have gas heaters?

[Chas]

No, but you're the closest.

What I mean is that the gas heater needs a pump to move the water through it - the larger the gas heater the larger the pump needs to be - so you are really heating with
Gas and electricity.

As a result, there is almost no savings at all unless you only heat once in a rare while or something like that.

[Chas]

Also, as has been stated, the cost of the heating appliance has climbed over the years - you can easily spend one or even two thousand bucks to get a mid-sized heater. And then the gas line will have to run from the meter to the heater. That gas line will need permits, and a pressure test, a trench, and finally plumbing from the spa to said appliance.

And as I mentioned above, a pump must be pushing water through the thing for it to work.