Reading reviews of tankless water heaters are an essential step in the purchase of a new hot water system. At the end of the day very few people will have the time or the will to become a true expert on hot water systems, but reviews will give you plenty of information to make a much more informed decision.
Many users see tankless gas hot water heaters as a black box of tricks and do not know much about what goes on inside. Yet this is a mistake because knowing a little about this can help you make a wise purchasing decision. What is more, the workings are not so complicated to understand.
For example, at a very simple level a gas tankless water is activated when you open a faucet (or switch on the dishwasher if it is rigged right). They take the cold mains water and heat it very quickly (not quite instantly, but in an impressively short time).
Knowing that a tankless gas water heater heats like this helps you know that two of the fundamental questions that any review must answer are - can it heat enough water for me? and can it raise the temperature from my mains temperature to a good level for my shower?
When you compare tankless water heaters (be they gas, electric or some other fuel) you are looking for the quantity of water they can heat and you need to match it to the quantity you need. You will not forget this if you visualize the water travelling through the unit, being fed through the narrow pipes of the heat exchanger and heat being applied to it. You can see in this image that each unit will have a limit to the amount of water it can heat.