I have been working with RUUD/RHEEM tank less water heaters (0.94 energy factor) with excellent results from the point of view of efficiency and performance. It keeps the temp at a constant, faster response, and the family has had no complaints at all. The most important my energy bills went down.
Thx, Jose, add in using solar hot-water then has a 100% backup, trying to get this across as a theme for off-grid, it's a key issue whether admitted or not.
Look at your SUMMER gas bill where water heating accounts for most of your gas use. 10-15 therms for most people, $10 worth of gas? If you spend $120/yr and tank gas hater is 60% efficient, you're saving maybe $40/yr by going tankless? Payback time exceeds life of water heater.
Guess you could get one of those $325 Marey water heaters that uses a 1/2" gas line and B vent, But you get what you pay for...
If you are going to stay with gas service, might as well keep the gas water heater. Switching gas water heater to electric should only be done as a larger plan to eliminate the $30/mo NG connection fee by going total electric. If you're not committed to an all-electric home, keep the water heater gas...
Most of the posts here are far too narrow in scope. To make the best decision you need to compare:
1. How much will it cost to operate?
2. How much will it cost to purchase and install and how long will it last?
3. How reliable, healthy, and safe will it be?
A tankless gas water heater versus the Marathon by Rheem:
1. About the same.
2. The Marathon will cost the same to purchase, but if your old water heater is electric the Marathon will cost a LOT less to install.
3. The Marathon is built to last much longer and be easier to service. And electric is safer than gas.
Another comparison might be between the Marathon and solar water heating. But a great set up would be using the Marathon as storage and back up for a solar water heating system. But it would be wise to compare these three points to see if the solar would pay for itself in its lifespan.
There are so many "green" options to choose from. There is no single correct answer. Its a matter of considering the pros and cons and how much each will cost to purchase, install, and service in its lifespan.
The marathon fails miserably in operating costs when compared to an ordinary gas water heater.. NG fuel cost is 1/4 of electric in our area. If you're paying the $30/mo service charge for the NG for use on other appliances, might as well get gas water heater also.
How does the marathon compare in costs to a heat pump water heater?
Biggest is to keep the CO or other gas down in building