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.

Viessmann vs. Energy Kinetics?

I lean toward high mass :P

Generally when I have used a low-mass boiler, especially one that does not modulate, but even with modulation it cycles at low load to a level I find, well, annoying. This is amplified when you are using TRV's and even a pressure regulating bypass valve which warms the return water. If piped P/S it can be better, but the flow rate at the boiler can be a sensitive thing.

Whenever I have had that problem the solution has been to add mass, (a volume or buffer tank). Key term is "well-insulated".

Sure, it may not respond as quickly to start, but once warm it evens out. Just my preference.

This is not a commentary on the manufacturers noted, just a preference of theory, experience and practice.

Other factors of distribution, building mass, proper sizing and so-forth also play a role.


  • joe_66
    joe_66 Member Posts: 30
    high mass or low mass

    whats better 2.4 or 52.6 gallons of water
  • J.C.A._3
    J.C.A._3 Member Posts: 2,981
    Thanks Brad....

    You can see Joe, I wasn't trying to p1$$ you off, just trying to get the feel for your system.

    With air handlers and SMALL radiant loads, a low mass boiler will cycle like a madman,and probably satisfy a low mass load need....in time.(modulation isn't an option with oil....YET!) A high mass boiler will do it's job in shorter "sprints". Like Brad, I see the same types of infighting between the 2 and if the MASS of the system will support a slower acting vessel, it usually makes more sense.

    Like a "flywheel", it uses stored energy to get the heating process started instead of always trying to play "catch up" to the demand. Make sense? Chris
  • Ragu
    Ragu Member Posts: 138
    I agree

    I've come full circle on this one and I now go high mass whenever possible. The short cycling issues on low mass boilers are a real annoyance (further study would probably also prove a severe drop in fuel efficiency and an increase on electric wear and tear).
  • B. Tice
    B. Tice Member Posts: 206

    I may be low-tech, but I think you should match it to the system. Modern house with some 3/4 baseboard loops where the hot water is a higher load than heat, low mass is OK. Big system,(Cast iron, CI boards,radiant) big boiler.Both EK and the big V are good products.
  • Rodney Summers
    Rodney Summers Member Posts: 748
    Mass is good

    But not in the boiler. You have to make domestic HW, so get a reverse indirect like a ErgoMax or Turbomax. Let those tanks be your mass in a thermos bottle. I just can't see heating up a high mass boiler off season just to heat up an indirect 2 or 3 times a day. During the heating season, there's probably no advantage since your cycling more often anyway.

    Of course, the low mass boilers don't break your back or the basement stairs and are easier to get into a tight space.
  • Ron Schroeder
    Ron Schroeder Member Posts: 998

    A high mass system has many advantages when the load is less than the firing rate. But using a low mass boiler and having most of the mass in an insulated vessel like a buffer tank or a reverse indirect (like an Ergomax)is FAR more energy efficient than having the thermal mass in the boiler due to much lower standby losses durring the off cycle.

    An EK boiler with a 50 gallon reverse indirect will use less fuel than the big V with any indirect. I have seen well over 50% savings in fuel usage in the warmer parts of the heating season and durring the non heating (DHW only) seasons with low mass/reverse indirect compared to high mass/indirect.
This discussion has been closed.