Question: how long does it take for a water heater to heat up 40 gallon?
Answer: While they can vary in size, the most common size of water heater is 40 gallons, which is what we'll be using here when talking about how fast they work. The bigger the heater, the longer they take to heat up the water. The average gas heater takes between 30 and 40 minutes to fully heat up the water in its tank.