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convert DHW indirect boiler to cold start?

icheat
icheat Member Posts: 16
in THE MAIN WALL
I have inherited a Burnham series 2 gas boiler that is currently dedicated for DHW, with 2 Superstor 80 storage tanks. It is currently configured as warm start: the boiler cycles between a high limit of 180 degrees and a low limit of about 160 degrees. The circulator and zone valves are activated by a Honeywell T775 on a call for DHW.

Everything is working well, although I have a feeling this isn't the most efficient way to have things set up (and my hot water bills seem pretty high). Should I consider converting this to cold start (by letting the T775 control boiler firing in addition to the zone valves and circulator), or would this be bad for the life of the boiler? Or should I try something else? Or should I just leave well enough alone?

Thanks for any advice.
AC

Comments

  • RobG
    RobG Member Posts: 1,850
    What type or application is this that you need two 80 gallon indirects with no space heating?
  • icheat
    icheat Member Posts: 16
    There is a separate boiler for space heating (the boilers are actually piped together with ball valves isolating them; I think this is to allow one of the boilers to act as a backup to the other in case something breaks, but this will likely be part of a totally different set of questions I have :smile: )

    This is a large residence, but even so the two tanks are overkill, and at some point (probably next year) I will remove one of them.

    Thanks,
    AC
  • icheat
    icheat Member Posts: 16
    OK, thanks very much for the advice.

    I don't have many good pictures, and its a lot of stuff crammed into a small space. Here is what I have at the moment.

    The first photo is the DHW boiler. The circulator is hidden behind the expansion tank. Most of the piping is for space heating. The vertical pipe with 3 takeoffs going to the right is the return, and only one takeoff is connected (the loop to the SS80 tanks).

    The second photo is the space heating boiler. The circulator is visible. The horizontal pipe in the back has 3 takeoffs for 3 main heating loops, and the return is the large vertical pipe on the right.

    The third photo is the SS80 tanks (in series, which is why I haven't just isolated one of them).

    The fourth photo is a closer view of the piping and vent on the DHW boiler.

    I don't know how easy it is to see whats going on from the pictures but I can try for better ones, or answer questions.

    Thanks again for all the help, I really appreciate it!

    AC

    wyo
  • icesailor
    icesailor Member Posts: 7,265
    icheat said:

    There is a separate boiler for space heating (the boilers are actually piped together with ball valves isolating them; I think this is to allow one of the boilers to act as a backup to the other in case something breaks, but this will likely be part of a totally different set of questions I have :smile: )

    This is a large residence, but even so the two tanks are overkill, and at some point (probably next year) I will remove one of them.

    Thanks,
    AC

    Why not just shut off the other tank and turn off the gas or energy to it. The same with the other "spare" boiler.

  • icesailor
    icesailor Member Posts: 7,265
    An excellent Piping Picasso.

    As far as running the boiler as a cold start, I would be concerned about the laws of unintended consequences. That no good deed goes unpunished. That if the tanks are connected to cold boiler water and there is a call for DHW, you can get a reverse transfer of hot water out of the tanks and in to the boiler. The other one is isolated. The boiler will still condense. Set the High Limit to 160 degrees and the Low to 120 degrees. You won't get the condensation on start up and you will save a ton of money.

    IMO.
  • icheat
    icheat Member Posts: 16
    icesailor said:

    An excellent Piping Picasso.

    Its even more impressive in person :smile: You can clearly see the work of at least 3 different hands

    I've turned the high limit down to 160 for now (the boiler aquastat has no low limit and a fixed differential, probably 15 degrees. I'll swap this out soon).

    Thanks for the advice.
    AC

  • icesailor
    icesailor Member Posts: 7,265
    Turning it down to 160 degrees is a good start. You could even try 150 degrees. If it gets Eskimo cold, you can just turn up the high limit to 160 or higher. Third World ODR.

    I just have a personal thing about a whole pool full of cold water going in to the system and running cold. Its actually fine and the lower you set the high, the closer it becomes to an old fashioned ODR or gravity system.

    IMO.

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