# Added Indirect Tank to Boiler Loop Need Help!



## ocyrus411 (Jun 24, 2018)

Hi all, 

I am a plumber of 10 years in British Columbia, Canada. By no means am I an expert at this trade, but I enjoy continually learning and challenging myself. 

Recently we had a customer who wanted to add a second hot water tank to his commercial apartment building (4 floors, low rise). His current situation was a gas fired 100 gallon tank, with a 400,000 BTU Super Hot conventional boiler to handle the space heating. The venting for the 100 gal was illegal as per BC code, as it was venting into the 8" boiler flue vent, which is illegal. Given the location of the 100 gallon tank, there would be no where else to vent it (except into the 8" boiler flue). This made my task to add a second 100 gallon tank more challenging, as I had no way to vent anything gas fired, and electrical was out of the question as the owner did not want to use power from a different building, he preferred to keep it separate. (This building is probably around 100 years old). 

So, I had the idea to branch a supply and return loop off the boiler, to feed a 100 gallon indirect water tank. I got the okay for this job. I piped the two tanks in series, with the first tank the indirect tank, and the second the gas fired.

This building is so old, there are no zone valves or thermostats in each individual units. Basically, the boiler runs on one thermostat (whether its a mechanical thermostat or outdoor reset control I don't know). This thermostat fires the boiler, and it sends hot water through the whole supply and return loop. The pump is running continuously, there is no relay on this setup. Whether the boiler is fired or not from this thermostat, the pump runs, and there is no bypass loop. 

The problem I'm having: I am afraid that when the aquastat in my indirect tank closes, it is firing the boiler, and because there are no zone valves or thermostats in each unit, and because the main boiler pump is running continuously, it is sending hot water to the units, when there is no space heating demand. So I have essentially overridden the space heating demand with the indirect tank demand :crying:

I am trying to think of a solution, and cost friendly, but it is difficult. I don't think it is realistic to install zone valves in every unit, but what about one for each floor that the supply enters? I'm not sure how the boiler loop is piped, if all the rads are in series or in parallel. 

Another idea I had was installing a bypass on the boiler loop (after my tee fore the indirect tank) putting the pump on the bypass. On the supply I will put a zone valve (after my bypass loop). So that way when there is no space heating demand, the zone valve will be closed. When there is an indirect tank demand, the space heating zone will still be closed. The issue with this idea: Where do I get a 2" zone valve to put on the supply?? Is there such a thing? 

Guys ... Would appreciate any and all input. I will be on the forum to co operate with any feed back, so if you spend time helping me I will try to help back with responding. I will post a picture shortly. 

Thank you!


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## MACPLUMB777 (Jun 18, 2008)

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## mass plumber (Oct 25, 2017)

UmmmNN
2- pumps with check valves. Pumps sized correctly


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## ocyrus411 (Jun 24, 2018)

MACPLUMB777 said:


> PLEASE READ THE DIRECTIONS !
> 
> 
> An intro is requested from all new members. In case you missed it, here is the link. https://www.plumbingzone.com/f3/.
> ...


I have posted an intro, thank you


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## ocyrus411 (Jun 24, 2018)

I ended up using a different relay on the fan center, and added a second relay to fire the boiler on indirect demand

the main pump is on the normally closed contacts, and the indirect pump is on the normally open. when theres a call for indirect tank heat, the pump relay is energized, turns off the main pump, turns on the indirect pump. G is split off my transformer, into a second relay. a 24v signal is sent to the boiler to fire, when the indirect zone valve end switch closes. 

despite the strategy above, the building is still getting heat when it shouldn't. i fear that when the indirect tank calls for hot water, when it is satisfied, there is hot water in the boiler distribution piping, when the main pump comes on, it pushes that hot water to the rads. i have to go back, my only solution i can think of is to put a summer switch between the main pump and the relay. they can turn off the main pump for the summer (vancouver summers are pretty hot/humid) and then turn it back on in the winter when they need heat. 

any other suggestions?

Thank you


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## ocyrus411 (Jun 24, 2018)

k, i had to go back again. 

what i did was wire the 2nd floor thermostat to control the main building pump relay. i wired the indirect tank aquastat to control the indirect tank pump relay. why didn't i do this from the start? i guess i thought i would only need one relay. turns out i needed two


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