DHW Coil Not Producing Enough Hot Water When One Zone Is Running - Plumbing - DIY Home Improvement | DIYChatroom

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Old 01-14-2012, 08:16 PM   #16
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DHW coil not producing enough hot water when one zone is running

Originally Posted by bubbler View Post
Aside from the DHW coil being physically installed in the boiler, there is absolutely no other connection to the heating system pipes. There are no valves, other other devices. I've taken a pretty hard look a the wiring, etc, and there is nothing that occurs when the zones call for heat that changes on the DHW side.
Your plumbing as shown is typical of a tankless coil. No connection to the zones at all.

Originally Posted by bubbler View Post
I'm leaning towards this being a scale up of my DHW coil combined with a faster rate of heat transfer from the 2nd floor (vs. the first floor). My suspicion is that because the first floor is made up of mono-flows the temperature of the water going back into the boiler (from the loop) is much higher, due to the mono-flows keeping some fraction of the water bypasing convectors), than the the temperature of the water going back in the second floor where 100% of the flow goes through the hot water baseboards...
I agree. The thing is, what is going on within the boiler. The tankless should be located in the hottest part of the boiler. If the temperature on the gauge isn't varying much, why the change in output from the tankless. It does take a lot of btu's to warm up water fast, maybe the boiler just can't keep up.

Did you check, does the temperature vary as much with just zone 1?

I bet if you can put in an electric you could plumb your own indirect.


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Old 01-14-2012, 08:19 PM   #17
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DHW coil not producing enough hot water when one zone is running

Originally Posted by Bob999 View Post
Really depends on the water quality.
With soft water (less than 1 grain per gallon hardness) the coil will probably never need cleaning. The more hardness in the water the more frequently it needs to be done.
This was my understanding as well.

Last edited by TarheelTerp; 01-14-2012 at 08:22 PM.
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Old 01-15-2012, 07:50 AM   #18
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DHW coil not producing enough hot water when one zone is running

Here's what I would do, purchase a 40 gallon electric water heater, hook it up, shut off the hot water loop to the heater, reset the aqua stat to disregard the hot water settings and just use the high low temp loops for heating the house. When it's all said and done it can be the best way to go, easy to troubleshoot, shut boiler down so many months(fuel saving), constant hot water temps when needed. Go for it.


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