What on-demand means
A tankless heater warms water as it moves through the unit. It can keep delivering hot water within its rated capacity, but the heater still needs to meet peak flow and the required rise in temperature.
Look at the busiest part of the day
Add up the fixtures likely to run together. An estimate based on one shower may miss a second shower, a laundry cycle, or a kitchen sink used at the same time. A technician can compare the combined draw with model performance.
Compare the installation and upkeep
Ask what would change for fuel supply, venting, and service clearance. Include maintenance and the cost of conversion when you compare the system with a new storage heater. If the main issue is waiting for a distant tap, ask about recirculation as a separate question.
