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High Mass vs low massBoiler

Wayco Wayne_2
Wayco Wayne_2 Member Posts: 2,479
I atended a seminar last night showing HTP's new product line. What caught my eye was the high mass boiler they call the Pioneer. Basically its a condensing boiler built into a buffer tank. It's basically the same design of the Phoenix water heater brought up to boiler specs and temps. I know Siggy has been extolling the virutes of this type of product for years and as far as I know this is the first one I've seen. Here in MD the plumbers just fall on the floor and go into a gran mall seizure when faced with understanding and piping a primary secondary piping scheme. I personally don"t underrstand the problem but I think this high mass boiler would help these poor souls out and build in a margin of error for heat load sizing challenged contractors. When installing a lot of micro zones the built in buffer tank is a handy thing to have. I think it would also be good on low mass heat emitters such as copper fin baseboard and kick space heaters. The low mass boilers excell when linked to high mass heat emitters like radiant floors and big old cast iron rads, but become more finicky when hooked up to low mass emitters. I think the more interesting question is, can HTP build in the quality we all craved through the hard times with other previous products. I also haven't looked into any price comparisons to the existing low mass mod cons, but my interest has been piqued.  


  • Mark Eatherton
    Mark Eatherton Member Posts: 5,853
    What concerns me...

    I have a serious concern over the combination of a space heating boiler, and the storage tank. When one or the other fails, you MUST replace both.

    I like the concept, in fact just recently tied a 400K modcon to an 80 gallon reverse indirect, that also does some base board heating in a basement, and the tank acts as a buffer. It purrs like a kitten, even at part load.

    But if (when) either component fails, I can simply replace just THAT component instead of having to replace both whether necessary or not.

    I realize that the Phoenix comes with a WHOLE lot of features that I would have to add to my design, and the simplicity is appealing, but in order for it to work in multi temp situations, AND provide DHW, it is going to have to be maintained at a fairly high stand by temperature.

    But overall, I like the concept of tying a modcon appliance into a large buffer/DHW tank.

    In reality, if our governing agencies would allow these manufacturers to do better than a 5 to 1 turn down, which IS feasible with most burner designs, no buffer would be required at all. Maybe it is time to revamp THAT part of our government, Complacency is not good for growth.

    TImes, they are a changin'...


    There was an error rendering this rich post.

  • EddieG
    EddieG Member Posts: 150

    On the Pioneer unit it is straight up heating. You can add domestic with a module that includes a plate heat exchanger with a domestic rated circ. pump. They call it the Versa Flame. I like the concept of high mass with a mod-con. But a lot of people have a bad taste left in there mouth. I went up to HTP a couple months ago and attended a local seminar a couple weeks ago and I must say I was impressed. They are trying to when contractors back. They have some nice features with the same control boards for all there units. Which you can plug your laptop in and check operation or program the board to the unit you are installing. I have yet to install any of there new products, but I have quoted them. I still have plenty of Voyager and Munchkin memories, but they always stood by there products and tech support has always been good. So we will see!!!!!
  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479
    Eddie G.

    Eddie, I'm sorry I missed you. I was invited to the same seminar, but I was out of town that day. I sent my son but got a limited report. I'm taking care of 2 Solar Phoenixes and they are working well. I too remember the Voyager days, and not too fondly.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I like the concept of high mass with a mod-con.

    I am not a professional contractor, and have experience with only one mod|con boiler (W-M Ultra 3), so that is the perspective I have. It is a low mass boiler, I suppose, since the heat exchanger (aluminum, small) holds only 3 quarts of water. It is cold start, and drives a high mass emitter (radiant at grade concrete slab) and a low mass emitter (Slant/Fin 2000). These run at different temperatures. Boiler has outdoor reset, and the reset curves are different for the two zones.

    There is no insulation on the heat exchanger, and the burner is totally contained inside the heat exchanger. Combustion air is piped in from outdoors, and the exhaust goes outdoors. Any heat lost by the heat exchanger heats up the incoming air, so it is not completely wasted. And the circulators run for a while after the thermostat is satisfied so that most of the heat in the boiler is pumped into the house.

    I have no problem with rapid cycling when the radiant zone is running, but when the baseboard zone, that has only about 6000 BTU/hour heat loss at extreme cold, runs, it would tend to cycle faster than I prefer. I found ways to reduce this by adjusting the maximum firing rate when that zone is running, and increasing the temperature limits from +|- 5F to +7|-8F. A larger mass boiler would take care of that, but that is what I have. (I believe changing the constants in the proportional-integral-differential control to slow it down a little would work too, but that is not an option.) The larger mass would confuse the control, I imagine, as it necessarily increases the delay in the feedback loop, requiring the gain to be reduced (lower accuracy) or risking instability. Also, the circulator would have to run longer to empty the hot water from the boiler into the house, or otherwise that heat would be wasted. At some point, that would result in wider temperature swings.

    It seems to me that when making changes in modern boilers, you cannot do things piecemeal because of the interactions. I do not know how many heating contractors know a lot about design of feedback control systems. I did that (not in the heating field) for some years and know of the challenges that must be met to achieve the desired accuracy, speed of operation, and stability. You usually get to choose two of the three. Sort of like pricing. Do you want good, fast, or cheap: pick two.

    Professional contractors probably have the experience to know if adding a buffer storage tank is a good way to fix a system that cycles too rapidly. It would certainly reduce rapid cycling, but it is not clear to me that the total system would work all that much better. I imagine it would depend critically on all the other aspects of the system.

    If my boiler would modulate down to 5000 BTU/hour, that would probably be a better way to reducing the short cycling in my system. But mine will go down (5:1) only to 15,000 BTU/hour.
  • EddieG
    EddieG Member Posts: 150

    I was with Ken Herne today. He told me that you were at the meeting last night and that your son was at the class with me. I wish I would have known your son was there, I would have introduced myself. I went out to HTP with Ken a couple months back and I was impressed. Believe me I have my concerns with some past history. But some of my biggest problems were with the local rep. and how they handled issues. With the Eklof being the rep., I feel a lot better.

    I also really like the concept of the Pioneer and Versa Hydro. I think they both have some great applications. They take away a lot of the issues that we have to deal with in certain applications. I personally am not a fan of using water heaters as heat sources. With this technology you get the benefits of a high mass like a water heater and the added efficiency like a low mass mod/con. Time well tell if they have corrected past issues.

    HTP has stopped production of the Munchkin. Which I honestly didn't have that many issues with. At least the few that I installed. However I have heard some horror stories and seen some that were not serviced that became nightmares. I think some of the biggest problems were caused because of lack of service and improper installations. New technology can be a great thing, but it requires service. Actually I feel some of the new stuff requires more service, compared to the older basic systems. A lot of contractors haven't stressed that when they have sold these higher end jobs.
  • Jeff12
    Jeff12 Member Posts: 1
    pioneer turndown?

    I got a Pioneer 199K to replace my circa WW II high mass gravity boiler. 

    I thought the terms "modulating combustion" and "turndown" meant that in  moderate weather (40-60 degrees) it would operate at less than 100% output to maximize efficiency.

    Mine starts at low speed and then speeds up ("shifting") every minute until it reaches top speed  after five minutes every time.  It never operates at anything less than top speed which I assume is full output except when starting up.

    The HTP rep who did the initial startup says this is normal.  I can't see where the modulation and turndown are?

  • hot_rod
    hot_rod Member Posts: 22,254
    I have a 2007 HTP Phoenix

    Solar Phoenix actually, that has been the ONLY heater that I have owned that fires, modulates down to the needed output and runs non stop all day long. Mine is an 80 gallon 130K, and my design load around 42K.

    My heating water is the tank and DHW is provided by an external 30 plate HX and a pump with a flow switch. I didn't want to keep putting fresh water into the tank.

    Solar input to the lower coil. I also have a wood gasification boiler input. So LP, Solar or wood as the fuel sources.

    I haven't done a thing to it in 7 years, I don't know that you can even service that spiral HX that runs up through the tank?

    I'll pull the burner one of these days and check flame rod, etc.

    In talking with a trainer from one of the premier German boiler manufacturers recently, those higher turndown rates are not so easy to run. Once the boiler is tuned for full fire the combustion numbers go south with those large turndowns. Doesn't sound like throwing a lot of technology, parts and complication is worth the effort to get a large turndown and keep efficiency up and emissions stable. He tells me the Germans pay a lot of attention to what products are out there, which fail and why. He claims the movement is back towards 5-1 turn down.

    With the exception of multiple burners and gas valves in larger output equipment, of course.

    I think the larger water capacity, however you decide to implement it, is the key. Lets not make them any more expensive to build and repair heating equipment with high tech sensors and emission sensitive control logic, on a 1 gallon fluid capacity heat exchanger :).

    Hydropulse was on the right path years ago too bad about then pulse combustion method, related noise and dependability, but the large capacity sure did match zoned or micro-zoned system very well.

    I think HTP, form my experience has it right as far as the concept and doable turndown numbers.

    Longevity is harder to predict, metal and weld quality are crucial, as is fluid quality, setup procedure, etc. Time on the job seems to be the only realistic way to determine what works and what doesn't. Hard to duplicate all the jobsite trama boilers experience, in a lab setting.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • SWEI
    SWEI Member Posts: 7,356
    More water, more better

    as far as the boiler is concerned (in most cases.)  Those old gravity systems worked surprisingly well with a bang-bang boiler.  They positively rock when paired with a mod/con.
  • tduby05
    tduby05 Member Posts: 1
    Any word on how these are holding up? Or recommend alternatives?