“Hot water supply boiler” defined.

“Hot water supply boiler” means a boiler that is completely filled with water that furnishes hot water to be used outside the boiler at pressures not exceeding 160 PSIG or at temperatures not exceeding 250°F at or near the boiler outlet and which: 1. Uses a storage tank to supply hot water to the system; 2. Fires on demand to heat water which is supplied directly into the system; or 3. Is fired at a rate of not less than 200,000 British thermal units.