05-28-2007, 10:19 AM
I am looking for some pros and cons for the purchase of a tankless water heater that will in the future be used for hydronic or radiant heat as well. We will need it to supply a shower, washing machine and heat simultaneously.
The popular brands in my N. Cal. region are Takagi and Noritz. Many plumbing contractors around here install Takagi but I don't know why.
05-28-2007, 02:15 PM
Tankless potable water heaters aren't designed for continuous use for heating...I personally think you are approaching this wrong.
Tankless has its place, and if your situation meets the right conditions, they can be okay. They are quite expensive compared to conventional heaters, and maintenance and repair can be high, and repair parts aren't available at your corner HD or Lowes - you'll need a specialist when it eventually (although it may be a long time) fails.
The things also are very dependent on the flow required, the incoming water temperature, and how soft the water is. Look carefully at the charts that show flow verses temperature rise. Find out what your worst case winter water temperature is. The more you want at the same time, the bigger the unit you need...sometimes, you need to run several in series. You will need a very significant gas supply (forget electric) and available free makeup air.
The outlet temperature will vary by demand and incoming water temperature. To prevent excessively hot water, you should install a tempering valve on the outlet to mix cold water in case the flow is small, since the water will be much hotter than normal. If it isn't sized properly for max flow desired, the water will be cooler than you want.
For radiant heat, I think you are better off with a boiler designed for that use. I'd spend the money for an efficient boiler with an indirect water heater. Get a quality one, and the standby losses are only about 1/4-degree per hour, so once hot, the thing doesn't have to run again for quite awhile unless there is a demand. The best boilers these days are in the mid-90% efficiency, are small, quiet, can be mounted in living spaces and hang on a wall in a closet.
Most tankless system do not allow recirculating pumps because that would keep them running constantly. I think using it for heat would be in the same situation. I'm not familiar with all of them, so that prohibition may not apply.
Compare efficiency of the tankless heaters with that of a true boiler. The increased cost and limitations may not add up.