HOT WATER ZONE OFF STEAM BOILER

Leaky

First, I apologize for earlier titling this "master plumber".  What an egomaniac.  Can you tell it's my first post?  Thanks for the input, hopefully more will come now that it's titled correctly.   Thanks.     -J.



I'll soon be reworking a hot water loop setup (3 zones) off a Weil-Mclain steam boiler.  The customer is tired of the water boiling in the hot water zones!  Elsewhere on this great site I learned I need to pipe a bypass between supply and return.  My remaining questions are:

Do I need to pipe a thermostatic 3 way mixer between supply and return, or will a throttled ball valve suffice?  <em>If I use the ball valve to mix, won't the HW temps be too low when there is no call for steam?</em>

Do I need to install another aquastat?  There is already a tankless coil aquastat maintaining 170 f all the time.  Won't that be sufficient?

Should I leave a flow check on the return?  Some information suggests I should, just to create head for the circulator.  The zones are controlled with zone valves.

Thanks to all for your input!

Steamhead

The aquastat in the loop

may not be needed if you're running that tankless. But you will still need the bypass to keep the loop below boiling when the boiler is steaming. If the boiler is not steaming, the weather is probably mild, and the loop should still work OK since the heat loss of the space is less during mild weather. 

Leaky

nice.

great answers, thank you.  I'll post again when I'm finished- hopefully I'll be getting to this within a week or two.

Steamhead

You might suggest

that the owners upgrade to a storage tank (fed from the tankless) or an indirect. Then the boiler would not have to maintain temperature all the time, and their fuel consumption would drop- especially in the summer!

Leaky

I'd been so caught up in learning

about this hot water setup that I hadn't even had that thought yet.  Good suggestion- and the indirect would be an easy option given the existing HW zones.  I'd have to check on the total BTUs required though.  The two tappings used are only 3/4" for the HW zones (currently 2)....  or I could put the indirect on priority zone...  thanks for the insight.

Leaky

It's done-

I successfully installed a bypass valve between the supply and return lines for the hot water system and added a purge station at each end just before the steam boiler.  A bit downstream of the mixed supply, a thermometer monitoring the outgoing supply water temp was installed. 



Now by monitoring the outgoing supply temp while the boiler is making steam and the hot water zones all calling, I have adjusted the ball valve on the bypass and also on the return to effectively set a " high limit" of approximately 195 degrees f.  When the system is not calling for steam and is maintaining for the tankless coil at 170, this locked in ball valve setup produces a supply temp of about 150 f.  Hopefully this will be enough to take off the chill on a milder day as Steamhead suggests, when the boiler is not calling for steam.  I removed the handle for the bypass ballvalve and let 'er rip.  2 weeks later, I don't think the customer has used the heat yet!  They are excited at the prospect of not hearing that "sound like a truck running into the house" (boiling in the baseboard) when running the heat though. it was not present during testing.



I apologize for not having photos to post, and I appreciate the professional insight and the opportunity to learn from you all.  Thank you.