Question: The specifications for installing a Bosch outdoor tankless water heater call for a minimum 4' clearance from any doors or windows. Why is this? And, do all manufacturer's have to adhere to this same standard?
Answer: The 4 foot figure is based on code. National Fuel Gas Code says (Section 10.8.2): “A mechanical draft venting system of other than direct vent type shall terminate at least 4 ft below, 4 ft horizontally from, or 1 ft above any door, operable window, or gravity air inlet into any building.”
And, yes, all manufacturer's of outdoor tankless water heaters must adhere to this same National Fuel Gas Code.