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possible conversion from 16 zone, 2 buderus g115 boiler to Lochnivar Knight - good idea?

acacioloacaciolo Member Posts: 9
Hello Everyone!

A few years ago, you guys helped me with some issues with my existing system. I am now thinking about changing it out, but I don't know if a low mass, condensing gas boilers is a good fit for my large system.

The system consists of 2 G115's with a 2017 logmatic control with the dual burner module installed. There are about 6 non mixed hot water baseboard/runtal radiator zones and about 10 mixed radiant floor zones. there also is 1 coil in an airhandler. They radiant zone manifold iscontrolled by a taco injector pump (can't remember the model number) but it has temp sensors strapped to the radiant side to control the amount of hot water injected. Every zone has a dedicated circulator and there is also a main system pump. There also is a 110 gall buderus domestic hot water tank .

All thermostats are tied into a home automation system so we have full temperature setback control in each room from the automation system. I am not using logmatic for any type of temp setback but we do use the outdoor reset.

total btu is about 240k, but it actually a little undersized. There were some additions put on this house and we relied on not all 16 zones running at the same time. So heating has been no problem, even in last year's bad winter. Based on the heat gain/loss, a 285k unit would be perfect.

given the fact that we have 16 circulator pumps and 1 system pump, I am not sure if a low mass modulating boiler is correct. I know they are sensitive to gpm flow, and with all zones active ( a rarity) I don't know if that much water flowing through works. In the past, i've relied on my local HVAC contractors, but this "old school" area still believes in massive, oversized, cast iron boilers.

I'd love to have 1 boiler that I can monitor via pc (which is why I like the knight.) But I know just enough to be dangerous. thoughts on a low mass boiler for something like this? My (possibly incorrect) thinking is that when only 1 zone is calling, the boiler can run at 20%, etc. So the modulating idea is appealing.


tony c


  • SWEISWEI Member Posts: 7,356
    The new Viessmann controls have Internet connectivity options. I believe Lochinvar is about to release one as well. Triangle Tube probably next year. In five years it will probably be a standard feature.

    I'd evaluate the piping and zoning as part of this upgrade. Zone valves use a fraction of the power a circulator does, and work quite well with ECM circulators. I'd also take a look at the sizing. With that many zones (especially if they're not all occupied at the same time during the coldest week of the year) you may not need that much boiler. Look for a high turndown ratio on the boiler (I believe Viessmann leads the pack at this time) or consider two smaller boilers again.
  • IronmanIronman Member Posts: 5,564
    Posting pics, particularly of the near boiler piping, always helps.
    16 zones almost seems ridiculous unless this is an apartment building or a mansion.
    Low mass is not an issue if the boiler is piped p/s and there aren't any micro zones. As SWEI said, two smaller mod/cons would be a better choice since that would give you a 10 to 1 turn down and also leave you some redundancy if one failed.
    I also agree that limiting the number circ's as well as zones would be prudent.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • acacioloacaciolo Member Posts: 9
    apologies for the crappy pictures. it is a very small room that has way too much stuff in it. It started out as a boiler room for an addition put on to a 2000sf house. and then another addition. and then another. and then another boiler. bottom line, there is 16,000 sf of heated floor space on 5 floors in this house. changing all the circulators would be a nightmare and the days of labor wouldn't be worth it. plus, if all 16 zones did call for heat, I can't imagine the size single circulator I'd need! So if I change this, I think I have to accept the fact that I am stuck with circulators. this room is jammed packed, so 1 con mod boiler would open it up a lot and make it much more serviceable. I am not worried about the energy cost of running those circulators, but I am worried about the smaller storage capacity of this boiler being able to handle the demand. (note...I know just enough to be dangerous) I've built about 350 houses, but most use a traditional boiler/hot water baseboard or geothermal. My regular hvac contractor is not up to speed on a complicated system like this. so it is up to me to do the research. thanks again!! note...most zones are individual rooms. 1000sf master bedroom with runtal radiators. 500sf master bath radiant. 800sf family room radiant and runtal. etc. so each zone is decent sized.

  • IronmanIronman Member Posts: 5,564
    acaciolo said:

    "I am not worried about the energy cost of running those circulators, but I am worried about the smaller storage capacity of this boiler being able to handle the demand. (note...I know just enough to be dangerous)"

    You have a misconception. The storage capacity of the boiler is a non factor. It's the OUTPUT of the boiler that matters. INPUT x efficiency = OUTPUT. You match the output to the total heat loss of the structure.

    The only advantage of a high mass boiler is if you connect a micro zone. With the high mass, short cycling is reduced, maybe eliminated. With a low mass, it can be a problem and adding a buffer tank is the common solution for a micro zone on a mod/con. The Knight also has control parameters than can be adjusted to help prevent short cycling.

    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • IronmanIronman Member Posts: 5,564
    Where are you located?
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • acacioloacaciolo Member Posts: 9
    awesome. I warned you...I know just enough to be dangerous! I am in NE PA, near allentown. The viessmann or knight are my top choices now...need to do some more research. I also need to understand the tie in of the existing taco controls for the obscene about of circulators I have.
  • SWEISWEI Member Posts: 7,356
    I'd be willing to bet that most of those zones are seriously overpumped. Take this opportunity to carefully evaluate the whole system before you start cutting pipe. A zone-by-zone heat loss will give you the required design temps and ΔT's for each zone. From this, you can explore your options for boilers, controls, and piping. We'll help you work through the process -- you may be pleasantly surprised at what can be done.
  • acacioloacaciolo Member Posts: 9
    that sounds like a great idea. the system was originally engineered by the guys at Tekmar (I used to use their controls.) I will take some measurements and do some calculations and report back. It is our big 150th playing of Lehigh/Lafayette this weekend (at yankee stadium) so I won't have any time until I recover from that. I'l post when I do. thanks for all the advice!
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