On-demand water heaters have been around for about the last 50 years throughout Europe and Asia, and they are finally arriving in the United States.
- These water heaters are very energy efficient because the unit fires up only when you open a faucet.
- Also, with a conventional unit, once you drain the hot water you have to wait for it to heat up again. But with a tankless water heater, you have hot water as long as the unit is running.
- In my own practice, I prefer the gas model over the electric tankless water heater. I believe that in terms of energy efficiency the gas heater is much more suitable to this type of demand.
Contrary to what you have heard, tankless water heaters don't need to be manually flushed every year. On-demand water heaters are self-flushing: Every time you use the unit, it's flushing water through the heater core.
It is true that the initial purchase and installation costs are two to three times higher than they would be for a conventional water heater. The good news is that the initial cost can typically be recouped within about ten years, through energy savings.
- Installing a gas on-demand water heater costs about $2,000 more than installing a conventional water heater.
- Installation is expensive because the unit needs a bigger gas supply than a conventional water heater does, and it needs to run its own exhaust flue to the exterior.
- Installation costs can vary widely, depending on the location of the flue and the gas supply.
- The unit itself costs between $800 and $1,000.
You will need to check with your local building department about restrictions. There is a limit on how many bends you can put in the flue and the total distance it can run horizontally or vertically. It can be sidewall vented to the exterior rather than running all the way to the roof, provided you have the setbacks from window and door openings that might be required in your county.
Here in the San Francisco Bay area I have not encountered building department problems when installing on-demand hot water heaters. Two years ago things were very different, but now I'm not aware of any cities or towns on the west coast that haven't approved these systems. I think now the ground has been broken with hot water heaters and people are increasingly receptive to their use.
For more information:
"Get Optimal Performance from a Tankless Water Heater" examines six of the most commonly-reported problems with on-demand heaters and provides solutions.
"9 Best Practices for Choosing and Installing a Tankless Water Heater" offers more practical advice on installing a tankless system.