hot-waterplumbingwaterwater-filtrationwater-heater
I have an instant tankless water heater, stibel-eltron dhc12, and want to protect the heating element from the high mineral content in my water.
A simple strainer may be good enough or a filter. What can I simply install on the supply side, which is 1/2" braided line?
I suspect you have a set-up like this?
You are concerned that when the water gets pumped back into the "water heater" it could possibly pollute your main water line?
The only thing I could suggest is putting a check valve on the "cold" water supply so that it can only supply fresh water. That is helpful if the pumps output pressure is higher than your supply pressure (This could happen on someday with low supply pressure or if you do not have main water pressure regulator)
In this situation the return is a dedicated port on the "water heater/boiler" and there should already be a check valve/pressure regulator/non return valve just before the water heater. So the rest of the house will run just on the cold water supply and never get any recirculation contamination.
We have a circulation pump that was in the house when we bought it. The instant hot water is nice, but it is a huge energy waster, as you suggested. Our solution was to put switches on the circulation pump. It's plugged into a receptacle near the water heater, so it was as easy as making that a switched receptacle. We have switches (timer type that turn themselves off soon after you turn them on) next to the shower and by the kitchen sink. It only takes about 30 seconds for the circulation pump to get the hot water to you, so we just turn it on while getting ready for the shower (or while stacking the dishes). So convenient, but without the wasted energy or water.
Best Answer
Your heater doesn't have a recommended limit on hard water, but I've seen others ranging from saying 7 to 12 gpg (grains per gallon) max. You need to find the hardness of your water before doing anything.
You can purchase hardness test strips, which are the easiest way to figure this out.
Water Hardness Scale
Treatment
Hard water is mainly caused by calcium and magnesium carbonates.
The most common way to treat it is with a softener, where "hardness ions" are exchanged for sodium ions in an ion-exchange resin. Essentially, the hardness is swapped with salt.
Cleaning
Your manufacturer should also have some cleaning instructions, where you periodically clean the heater elements. This is probably every 1-5 years depending on water quality.