Sizing a tankless water heater may look tricky at first, but there are a few steps to finding the right one for your home and situation. The correct water heater, whether conventional storage tank or tankless, will ensure that you have hot water when and where you need it. Tankless water heaters are rated by temperature rise and flow rate, in other words, how hot the water gets and how much is used at once. You need a water heater that heats enough water hot enough for each device that’s expected to be used concurrently. Consider the following: