Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Thermal Shock

Mike R.
Mike R. Member Posts: 12
in THE MAIN WALL
A question was recently posted asking about Thermal shock to a hot water boiler due to a multi-zoned system with hot water cast iron radiators. Does a single zone also experience thermal shock?

I have 137.7 feet of Baseray baseboard hot water cast-iron radiators which hold 41 gallons of water (0.3 gal/liner foot). I am getting a new oil fired hot water boiler, probably with indirect tank (decesion still pending). If priority zone is given to the tank and the other zone to the radiators, do I still need a SYSTEM bypass? What about boiler cold start?

Comments

  • Al Letellier
    Al Letellier Member Posts: 781
    thermal shock

    Thermal shock relates to system vs. boiler volume. If you are going with demand start with domestic priority, it will normally not be a problem. A very low mass boiler with high velocity in the system could be subject to thermal shock, but it's unlikely in a small residential application. It usually occurs in old large gravity or hot water systems with a low mass boiler.
    There are several good boilers out there designed for low temp return with no danger of thermal shock. Consult a good contractor about your particular application

    To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"
  • Jay_12
    Jay_12 Member Posts: 46
    Thermal Shock

    Cast iron boilers without some type of protection can be shocked if any one zone if off for any length of time. This can occur from any zone being on a night setback or possibly from priority for the DHW storage tank. For example, the boiler is hot (180F) from priority heating a DHW tank. The DHW tank heat call goes away, allowing the other zones to turn back on. Now if those zones have cooled off so that the water is "cool" such as 80F, then the boiler experiences a 100F temperature change from inlet to outlet. This is thermal shock.

    Now a boiler bypass can be installed to protect the boiler. However, since the bypass is fixed, it can lead to short cycling on the boiler, thereby creating extra wear and tear and increasing your fuel costs.

    The best way to deal with this is to add an automated mixing device such as a mixing valve or a variable speed injection loop and pump. This way the automated control can restrict cold water from entering the boiler and you get the added benefit of outdoor reset.

    If you have any further questions, please contact me. 1-250-545-7749 www.tekmarcontrols.com

    Jay
  • Joe@buderus
    Joe@buderus Member Posts: 165


    Consider a Buderus G115 Boiler with one of the Logamatic Control. The 2107 is an outdooor reset control and the 2109 control is a cold start. Both of these controls feature "Pump Logic". This feature will shut the circulators down if a minimun temperature of 105 degrees cannot be maintained when the burner is firing. While this feature is designed to prevent flue gases from condensating in the boiler, it also can assist with thermal shock. Because of the cast iron (GL-180M) used in Buderus Boilers, which is flexible, as well as corrosion resistant, we are more resistent to stress from thermal shock.
    If there are any questions please feel free to contact us at 1-800-283-3787.
This discussion has been closed.

Categories