Looking at installing a whole house gas fired instant water heater, about 6 gpm. The plumber is telling me that they foul fairly quickly due to the hard water in the area (water softeners are very common). Anyone able to confirm this? He says that the tank-type heaters are better because the sediment settles in the bottom and reduces the holding capacity, but doesn’t affect the heating. He says he talkked with his rep at the local (large) plumbing supply, and the rep says they have only sold 10-12 in a year and a couple have had problems. IMO the plumber is playing games for some reason and just doesbn’t want to install the instant heater. Since I’m not a licensed plumber, the supply houise won’t sell to me (I already asked), so it would be provided and installed by the plumber therfore he would have some inherent guarantee, and I think he doesn’t want any risk.
Do it right, or do it twice.
Replies
I don't have personal experience to support the plumber's claim because the area in which I live does not have hard water, so I did not have fouling problems with mine for the few years it operated. What he claims, though, is not unreasonable. Unlike most solids, calcium and magnesium compounds (called "hardness" in water) are less soluble in water as the temperature rises. Since the temperature of the water within the tubes is greatest at the inner surface of the tube (because there is flame on the outside), these materials are the least soluble there and thus percipitate out onto the wall of the tube. It's a very real effect on commercial high pressure boilers, one that must be protected against by water treatment. So, I would believe it's possible in household water heaters.
I don't remember my chemistry well enough, but I believe that sodium compounds are more soluble as the temperature increases, so if the water were softened first (softening replaces calcium and magnesium with sodium) then the minerals in the softened water (sodium) would not percipitate out on the walls, and there would not be fouling.
If there are water chemistry experts out there, they may have more to say. Or people who have tried these heaters under hard water conditions.
Elcid--
My plumbing sub here says the same thing. We don't install them for anybody on a well, only people drawing from a lake.
I'd go with a tank heater. If you go with gas, don't forget to have him change the standard dip tube for a J model (see Peter Hemp's article in FHB about three-four years back). It keeps the sludge and crud from accumulating so fast in the tank.
Dinosaur
'Y-a-tu de la justice dans ce maudit monde?
I wear if you clean them out with vinegar yearly it helps with the fouling
Daniel
A tankless water heater requires a heat exchanger with small passages (in order to heat the water quickly). Since the scale from your water deposites on hot surfaces, the heat exchanger of a tankless heater would be a prime spot for scale to build up. That will really limit the performance of the heater.
By the way, you said you wanted a 6 gpm instantaneous heater, unless you live in an area with very warm incoming water, I don't believe that flow rate is possible with a normal gas line. I suggest you double check what temperature rise is being quoted at 6 gpm.
Thanks to all for the replies. The water is from a well, and here in south Texas it stays fairly warm, so the 6 gpm is probably attainable. And it would be heated with propane. Since the HO does not have a water softener, we may have to go with a tank.
Do it right, or do it twice.