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kchamb1206 09-04-2010 10:11 PM

Adding Hot water Heater To Boiler
I have a boiler that heats the domestic hot water with a tankless coil. Burning oil in the summer drives me crazy so I'm adding a GeoSpring hot water heater in line. I'm wondering whether to put the hot water heater before or after the boiler. Seems like 6 of one and 1/2 dozen of the other. I plan on shutting the boiler down in the summer. Does anyone have a case for one or the other?


beenthere 09-05-2010 04:45 AM

If you put it before the boiler. Then you will be heating the boiler every time you tap hot water, and end up not having hot water.

The coil in the boiler is not prejudice and doesn't care which way it transfers heat.

secutanudu 09-05-2010 08:23 AM

Also, if you put it before the boiler, you will not gain efficiency in the winter when your boiler is I'd put it after.

AllanJ 09-05-2010 08:57 AM


you'll be heating the boiler
This part is critical. You must put the stand alone water heater after the boiler so in summer the water out of the live water heater doesn't get cold again passing through the dead boiler.

Now the stand alone water heater has to stay live during the winter. It will use far less energy with the incoming "cold" water preheated by the boiler, but overnight the water may cool off too much in the tank if the standalone heater is dead.

Another option is to install a network of (manually operated) valves so the water goes through the boiler only in winter and the stand alone heater only in summer. Relating the setup to electrical hookups, this is called a parallel connection. When the water has to go through both places, that is called a series connection.

NHMaster 09-05-2010 11:01 AM

If you are going to keep the coil in the boiler than I agree with Alan. If it was me though I would cap off the tankless coil, cold fire the boiler and put a re-set control on it. Even though the boiler is hot in the winter, that hot water from the tankless coil is not free. Any time you run cold water through it, you drop the boiler temperature and the burner comes on. You will save the most money by following my advise above however, just to give you something else to consider.... If your boiler is fairly new and efficient, installing an indirect water heater off the boiler will save you more money than the electric water heater will, especially if you cold start the boiler and go with re-set control.

kchamb1206 09-05-2010 06:44 PM

Thank you gentlemen. You'd think a guy who's had a least 3 physics classes in his life would think about heat tranfer being a 2-way process, but that as a long long time ago.

So after the boiler is the way to go. This boiler is at least 50 years old so I'm not sure about adding an indirect water heater. I have to have the annual service to the burner soon so now I have some options to discuss with the boiler tech.


the_man 09-05-2010 08:21 PM

yea definitely after, I like the idea to rig up a bypass system so you can run one, the other, or maybe both at the same time. Options are good for you and possibly the next homeowner too (resale value)

NHMaster 09-05-2010 09:08 PM

I have to assume that you are considering the water heater to save money? but it may be a combination of saving money and getting more and better hot water also. If your boiler is 50 years old, don't spend another dime on it. Replace it. Look into a buderus with indirect or a system 2000. That old crap is doing nothing but burning dollars every time it runs.

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