Considerations for tankless water heaters are; they are very small (not much larger than a microwave oven), you get an unlimited amount of hot water (you can fill a swimming pool and the hot water will never stop), and tankless water heaters will save you gas since most tankless hot water heaters don’t have a pilot burning 24 hours a day and they use gas only when you want hot water.
You may want to install a tankless hot water heater when you want to turn an existing water heater closet into a linen closet, when you are re-piping (installing new water pipes in your home) and the tankless water heater and installation will be cost you less since your plumber is already working on your pipes, when your existing water heater will not give you enough hot water during peak demand periods, and when you want to relocate your existing water heater outside and you want a small water heater that is not as unsightly as a large water heater large exterior housing.
While most tankless water heaters look the same from outside their shell, there is a significant difference on the inside, and even their cost. You will notice the reason for these differences when the tankless heater fails to operate and obtaining service is nearly impossible. The service for many of the better brands is terrific
Rinnai Model 85e TANKLESS WATER HEATER
The advantages, over a conventional 40 gallon gas tank-type heater, are the Rinnai 85e is only 9 inches deep, 14 inches wide, and 24 inches high. The Rinnai 85e delivers up to 8-1/2 gallons of water per minute, continuously, and it uses approximately 30% less gas. So, you will save on space, save on gas, and you will never run out of hot water.
When installed outside, the Rinnai 85e does not require a vent (smoke) pipe through the roof. The Rinnai 85e requires a 3/4 inch gas pipe. When you have an existing tank-type water heater the gas pipe must be changed from 1/2 inch to 3/4 inch sometimes all the way to your gas meter. This Rinnai 85e requires a 110 volt electric outlet in the vicinity of the heater.