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Installing a bypass in an existing system

Customer's house is a bungalow, built in 1930s, cast iron radiators with 1" copper supply with diverter tees. A Buderus G115, 4 section boiler with no bypass, installed sometime in past 5 years. Have seen two different recommended ways to pipe a bypass: Buderus recommends installing bypass before circulator (which is on supply). Another recommended way is installing bypass after circulator (which is on supply) and before a valve on supply with note to adjust valves to maintain 160* F or greater in boiler (there is also a valve in the bypass piping). What is the preferred method for this system ? Is there one preferred method for all types of systems, or does the method of piping a bypass depend on the circumstances ?

Comments

  • FranklinD
    FranklinD Member Posts: 399
    I prefer the boiler bypass (piped into the auction of the circ). Bypasses most of the system water around the boiler, slowing the flow through the boiler to allow it to pick up more heat. I just installed one on my Burnham last week. Works beautifully. 90* return, 140* coming out of the boiler, and 115* at the tee where they combine. Boiler takes 15 minutes or so to hit the 150* high limit (set by on board ODR), then cycles the burner off and runs 10 minutes or so before cycling the burner on again. More fine tuning to come as winter temps arrive, but happy so far.

    I have big radiators that don't require high water temps to heat the house, thus the low water temps.
    Ford Master Technician, "Tinkerer of Terror"
    Police & Fire Equipment Lead Mechanic, NW WI
    Lover of Old Homes & Gravity Hot Water Systems
  • JUGHNE
    JUGHNE Member Posts: 9,750
    FranklinD, what is the temp of the water going into the inlet of the boiler? I assume we are talking cast iron boiler?
  • Bill_17
    Bill_17 Member Posts: 68
    Here's another option, two sizes and several thermostat choices to best match the required flow rate and temperature.
  • FranklinD
    FranklinD Member Posts: 399
    I haven't had the low temps yet this year to properly set it up yet, but the short answer is, it depends. As of right now it's been around 90-100* on the return to the boiler and 110-120* on the supply (after mixing in the bypass tee). The 90-100* is under the 110* 'minimum return temp' listed by Burnham but I'm fine with it as long as the flow isn't excessive. The delta T from return to supply through the boiler is about 40-50* so the average water temp is around 120-130* which is within the manual's specs (110 return, 130 supply - minimums).

    Not great, but it'll do me for the winter. Much better than last year with no bypass, and months of running 90-130* water through the boiler at 8gpm.

    Kind of waiting for my water heater to die so I can purchase an indirect and plumb it up. At that point I'm thinking about replacing radiator valves with TRV's, plumbing the boiler in P/S, adding constant circulation, and maybe a 4 way valve for temp control. It's all up in the air at this point.

    Yes, cast iron boiler (Burnham ESC). I intend to diddle with the system as finances allow, and eventually switch to a mod/con.
    Ford Master Technician, "Tinkerer of Terror"
    Police & Fire Equipment Lead Mechanic, NW WI
    Lover of Old Homes & Gravity Hot Water Systems