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Hydronic heating retrofit project using Viessmann boiler and steel rads

smihailasmihaila Member Posts: 93
Hi everyone,

First of all, I would like to thank to those who have made the existence of forum possible, and to all the members of this wonderful community for allowing me to read useful info and to post my first message here.

I hope you can help me with a retrofit project that I'm planning for my house (I live in Waterloo, Ontario, Canada). I am originary from Europe and it's suffice to say that I'm not keen to the forced air heating systems which you can commonly see here in North America. I grew up with hydronics and I'd like very much to install such system here. [I apologize in advance if my message will be too long.]

I'm thinking about using a Viessmann Vitodens condensing gas boiler (either the WB1B-26 or WB2B-19 model) and classic radiators (steel panel rads). I am not an HVAC professional (I'm only an IT guy) but I am counting on the help of my father (who is about to come here in Canada within a month). My father is a "jack of all trades", being crafty in masonry/construction, general mechanics, and even plumbing and gas. He has done more than twenty hydronic installations back in Europe.

There are a few "variables" with our new project:

-First, the hydronic systems which my father had done in Europe were mostly involving integrated systems. For example, no external pressure vessel or external recirc pumps, no hydraulic separators or closely spaced tees, not too many heating circuits - everything came integrated with the (system) boiler (which is called over there also a "central heating system/station"). Also, he was never involved in projects dealing multi-zoning and motorized control valves. But he is very good at installing a basic heating system (one primary circuit), pex-AL-pex and Copper piping, radiators, gas fitting and so on.

-Second, I have asked for several quotes from some local companies here in Canada, and the prices seemed skyrocketting and there wasn't too much flexibility in terms of rads sizing, thermostats, zoning etc. That's why we decided to go with a DYI approach. Now, because I am not a (licensed) company, I have tried IN VAIN to get some prices for individual parts such as steel rads, Viessmann boiler etc. I don't know how it is in US, but in Canada it feels like a 'cartel' and protectionist markets and simply put, no company wants to speak with me once I tell them I'm a residential customer. And paradoxically, the Viessmann Canadian headquarters are located at 3 miles from my location. Also, the main Canadian distributor for Biasi / Quinn radiators is in nearby (60 km). None of them wishes to do business with me directly. I am telling you this because this is a factor which will influence A LOT the cost figures for the project - since I'll be forced to buy via some US located stores, eventually online - i.e.

Now, please allow me to indicate Manual J calculation results. I have used the wonderful HVAC-calc software and I chose "average" as infiltration level. It's a 2-storey house, 16 years old, 2x4 timber frame construction, about 1470sqf usable space (without basement). The design conditions were for Kitchener, Ontario, Canada: outdoor summer temp = 85F, outdoor winter temp = -2F, summer grains of moisture = 98, indoor summer temp = 75F, indoor winter temp = 70F. And the total heat loss resulted as 30,533 BTU, which with a 20% additional safety factor would be 36-37 kBTU/h. The calculations were done considering triple glazed window (using good German uPVC tilt-and-turn profile with Uw = 1.2) and R-48 attic insulation (closed-cell sprayed foam insulation).

I could attach the detailed PDF report, and also the exact BTUs needed per each room, if you wish to see more details.

The old forced air furnace (came from the builder) was sized for 50,000 BTU. Another contractor (when I was still contemplating the idea of going with forced air via a new system using a mod-con furnace like Trane) was doing his own Manual J calculations and said that he would go with a 60,000 forced air furnace.

The main idea is to install about 12 or 13 radiators (3 in basement, 5 main floor and 4 or 5 upstairs), route them using a combination of manifold and reverse supply-return connection, via either copper or pex-al-pex (this has yet to be decided) and use either only one zone for everything, or design 3 zones (one per each floor) and have thermostats (Vitotronic remote 200 ? - which is a bit expensive) on each floor.

We aim for a low system design temperature - 130F supply and 110F return, to increase the overall fficiency of the system. But somehow at the expense of larger rads. We would have only one primary heating circuit. There is no need for any secondary like DHW because I have already a separate Rinnai RC98i tankless water heater for that.

I'd like to ask you a few questions, maybe you can help:

1. Which Viessmann boiler is more appropriate for that heat load (to avoid short-cycling): WB1B-26 or WB2B-19 ? I also understand that the WB2B comes with that outdoor reset sensor and the Vitotronic 200 can offer better temp control overall. The only drawback that I see with WB2B is a higher cost plus the lack of an integrated recirc pump.

2. If we were to go with WB1B-26, would that internal recirc pump be enough for the whole system (acting as a boiler + system pump) or in fact you have to use an external one? If we go with WB2B-19, we would have to use an external pump anyway - Viessmann product docs recommend Grundfos UPS15-58F, Taco 00R or

Wilo Star S-21FX - either of them priced at around $100 at

3. Is a primary-secondary hydraulic separation really needed? Things like low loss header or closely spaced tees? As I said, there will be only one circuit - we wish only to heat the house via those 12-13 panel rads. When I look at some installation examples via youtube or via heatinghelp, I must admit that I get scared a bit of the complexity (mixing valves, differential pressure valves, 3 or 4-ways diverting valves, low loss headers, zone pumps and many valves on and on). Should it be really that complicated - considering our needs ? :-)

4. Is there any special sizing formula for choosing a pressure tank? Can I chose whatever is at

5. Is a multi-zone system really necessary (motorized valves and controller)? I'm afraid a bit of this topic because by father has never used them so far. What I basically wish to have is this: in the basement turn the heat completely off, or very low (since we don't visit it too much for the moment), in order to "route" more heat to main and upstais floor. Many people were telling us that the zones will create more flexibility and comfort and you can still use only one recirc pump. My father says that we could simply turn the heat off by adjusting some valve at the manifold in the mechanical room in the basement :-). Could you recommend some good zone valves and their controllers?

6. Would you be able to recommend what other things would be needed, at a minimum: besides one recirc pump and one pressure tank, what other valves and sub-systems would you recommend? Is a mixing valve or differential pressure stuff needed?

7. Could you recommend better US suppliers, eventually available online (I don't drive for the moment and have no car, shame on me), with better prices?

8. Is store to be trusted? Has anyone had experience with them? They seem to have good shipping rates to Canada (300-350US via LTL truck) and I could engage a customs broker to clear the stuff at the border.

9. Would you go with copper piping or pex-AL-pex? It's funny that Europe started with pex first and now they use copper everywhere. And in north-America it's exactly the opposite. My father wants copper (me too I like it due to being straight and rigid) but I tried to tell him that 1 meter of hard "L" copper pipe costs about $7.90 CAD for 1/2'' and $14.50 CAD for 3/4''. He said we would need about 10 meters 3/4 and 40 meters 1/2. Is that way too expensive comparing to pex-AL-pex? What I like about pex-AL-pex is that it will survive better in the basement against freeze and also being plastic coated, it will keep the hot water warm and less losses on the circuit until it gets into the rads. On the other hand, pex can't stay perfectly straight (looks uglier below the rads) and the pex fittings cost more.

There would be many other questions, such as if my 130/110F system design temp is a realistic one and if my calculations for the rads are ok (that is, if they cover a worst case scenario). But I'll leave other questions for later because I already wrote a whole story here :-)

Thank you everyone for your time and I appreciate all your insights.

[kindly see the PDF attached]



  • Paul PolletsPaul Pollets Member Posts: 3,022
    edited March 2013
    DIY system

    Trying to put a system together as a DIY'er can be difficult, no matter where you are located. Some manufacturers (including Viessmann) will not honor a boiler warranty that has been purchased over the internet. This does not stop e stores from selling and discounting them. This could leave you in "hot water" if there is a problem with the appliance.

    Wall panel radiators need to be sized for a condensing load. That means the radiator will heat the room at design temperature using 140 degree water rather than 180. Their are charts and multipliers that the radiator manufacturer provides to do this. Usually the radiator increases in output and size by 30-40% to work at lower temperatures.

    The Vitodens works best with a low loss header. I always use a variable speed pump on the radiator circuit (ie, Grundfos Alpha) and a 15-58 3 speed between the boiler and the LLH. Installing TRV's on each radiator works best, and 1 thermostat will be required. I use copper to pipe the boiler and pex-al-pex for distribution piping to the radiators. I'd use a 60g extrol tank with 12-15 radiators. The Vitodens 100 also has an outdoor sensor and an integral outdoor reset control. The 200 model has more bells and whistles and allows multi temperature operation of the heating circuits with automatic mixing valves, if required. Neither boiler model comes with a pump(s).
  • smihailasmihaila Member Posts: 93
    edited March 2013
    Thank you for the feedback

    -About the DYI approach and invalid warranties, I am aware of that and unfortunately there aren't other viable alternatives, so I'll have to take a chance...

    -Regarding rad sizing, yes, as I was mentioning we aim for a low system design temp, ideally 130F supply / 110F return. And yes, we have to use some correction factors for the rads. For example, the Biasi rads should have their official BTU values multiplied by about 0.5 @ 140F or 0.45 @ 130F supply tem. Some hydronic suplying companies (such as "Hydronic Alternatives") were suggesting that 130F is "pretty aggressive", saying also that  "it's a point of diminishing return when oversizing the rads".

    -Based on what you explained, it is in fact expected to have to work at lower temps, for the Viessmann condensing boiler to reach a condensing stage. Do you think that poses also a min limit that must exist between the supply and return temps (a min DeltaT)? That hydronics company was suggesting that 140F would be more achievable, what do you think?

    -About the hydronic circuit: so you are definitely proposing the use of a LLH even when there is only one heating circuit overall? That LLH model made by Viessmann - the smallest one rated at max 17gpm and 80/50 factor?

    -And besides the 15-58, tri-speed pump used as a boiler pump, you are also warmly suggesting a variable speed pump in the rad circuit, after the LLH? What is the advantage of using a variable speed pump? It it because the heating circuit will have a variable load/pressure, depending on how many rads are "turned on" by the thermo-static valve (if only one zone is used) or by the zone valves? Could you please be kind and advise me on what exact pumps to go with? Also, is there a preference over a certain brand - Grundfos, Taco or Wilo Star? Which one offers a good balance between price, quality and power saving?

    -What would happen if only one pump for the whole system is used i.e. the 15-58? The house is two-story, and there would be 12 or 13 rads.

    -About TRVs, to be honest I am a bit reluctant in using them, because their lifespan isn't great, and you have to do some maintenance on them each year to make sure the wax stuff doesn't get "stuck"? Would zone valves be better? If they are to be used, how will the valve controller interact with Viesmann's on-board controller? Basically as long as I don't plug a remote thermostat into the Viessmann boiler, there will be no fight for control, right?

    -You were recommending TRVs plus one general thermostat plugged into Viessmann, right? Is it important for that thermostat to be a Vitotronic 200 ? Or there are other cheaper brands that could be used?

    -Pressure tank: extrol 60g it is then. Thank you for the hint !

    -Piping: we are still debating between pex-al and copper for the runs to the rads.

    -Viessmann 100 vs 200 models: I did not know that not even 100 comes with a built-in pump. About the Outdoor reset sensor, I knew that it's compatible with 100, but was not aware that it comes as standard package (I thought that one of the reasons for the 100 being lower priced would be because Viessmann tried to skimp on some options/standard package?)

    -For a total heat load of 35-36 kBTU/h, what would you personally chose? WB1B-26 (rated up to 93 kBTU) or WB2B-19 (rated up to 67 kBTU)? Wouldn't the WB1B model be oversized/short cycled? Btw, I don't understand why a forced air furnace is sized for almost the double of the heat load needed and a hydronic boiler sizing criteria follows different rules? Or the rules are the same?

    Thanks a lot for your help and sorry for so many questions.


  • RobGRobG Member Posts: 1,850
    DIY Project

    You might consider hiring a consultant to assist you in your project. He can do a piping layout and help you in sizing the proper system. He can probably help you in acquiring equipment as well. One such company is Northeast Radiant Technology. NRTRob runs that company and posts here quite frequently and is very knowledgeable. It can't hurt to make a phone call. 

  • ChrisChris Member Posts: 3,056

    The max flow rate through the WB1B10-26 or the WB2B-19 is 6.1gpm so you should be using the low loss header. You want to use it with the Vitodens 200 as there is not "TT" on the boiler and the boiler will fire if the system temp drops below the system side need.

    I'd be running this on constant circulation and be using the WB2B19. There is a pump output on the boilers power pump module to power a single circ relay. It will power the relay constant as long as you are below warm weather shut down.

    The boiler will condense don't worry about that. Design for 140 on the system side, run constant circulation using a Taco Bumble Bee set for a 30 and let it rip. I would be using thermostatic valves with built in by-passes with my rads piped home run via 3/8" pex using a radiant manifold. Keep it simple and smart and you'll have a great system.

    Unlike across the pond no variable speed built in boiler pump here in North America. The 200 sports lamda pro which will optimize combustion no matter gas quality. As our great utilies pump in fillers the boiler will pick up on it and adjust accordingly maintaining a nice clean burn.

    You may want to opt for the Vitotrol 300 in the main space providing it's an open floor type plan. The control will provide indoor temp feedback to the boiler so it can tune in the needed supply temp based off the combination of the outdoor temp, indoor temp and supply temp. It will allow you to program heating schedules similar to a thermostat so you can do set back effectively. The Vitotrol is basically an extension of the boiler control. Will provide fault codes and give you some control over domestic hot water as well if you are installing a indirect.

    The new version 200 slated to show face here in the very near future sports the control being used across the pond and with it comes VitoCom giving control via IPhone/IPad and Android ap.

    You picked a quality boiler and like they do across the pond, keep it simple and effective. You'll be happy.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • smihailasmihaila Member Posts: 93
    Boiler and pumps

    -Ok, I didn't know that the LLH is so important, even when only one heating circuit is being used and the flow rate relatively constant. I was afraid of using it, thinking somehow that this would waste energy (boiler continuously running its small loop and losing a bit of heat via the LLH's casing and not transferring the full thermal energy to the rads). Many thanks for this tip - I'll use one, together with that thermistor/sensor as well. This will help the boiler in correlating even more the ODR with what's going on inside, and thus be able to reduce dynamically the operating supply temp and not creating temp fluctuations in the room.

    -I'll go for WB2B-19 then, thanks!

    -I'll strive for 140F system temp.

    -When you are referring to "constant circulation" and associate that to "Taco Bumble Bee for set for a 30" you are implying that a 2nd pump has to be used, in the whole rad circuit, right? Please pardon my ignorance, what is "set for a 30"? Is that pump a variable speed pump?

    -TRVs, ok dully noted - I'll try to find a model that has built-in bypass. But I think both Biasi and Pensotti rads have that flow regulator built-in and the only thing missing is the TRV which you attach to that flow restrictor?

    -Interesting observation about no built-in variable speed pump for North-American model. But, the question would be: are the boiler's internal controls able to drive an external var speed pump and modulate the flow dynamically? Is that "Taco bumble bee" supposed to achieve that? Or such pump cannot be plugged into the boiler's internal power/pump box and has to run independently, and rely on some "factors" directly from the water circuit, in order to know when to start and stop?

    -I didn't know that here in N.A. the gas utility companies would start adding fillers/air to the gas supply - on contrary I would've thought that the distribution here is more uniform than in (Eastern) Europe and that they would be more honest, hehe :-)

    -Vitotrol 300 - ok, so you think that I would need only one? For the main floor/living room area? And a 2nd one upstairs is not needed / not even know if possible to connect to the same KVM bus from Viessmann?

    Thank you again to all, for the great advices.
  • ChrisChris Member Posts: 3,056
    The Bumble Bee

    Is a delta-t pump. It is supplied with supply and return strap on sensors. It will maintain your design delta-t as your TRV's open and close by on the pumps logic not from the boilers logic.

    Your boiler is going to control the boiler pump which could be another Bumblee Bee but you would have to run it in one of the fixed speed modes. Still will use less electricity then the standard Taco 00R which would be the correct boiler pump.

    You can run multiple Vitotrols and Viessmann does offer a KM Bus Module that is basically a place to tie them in and then from the module to KM Bus on the boiler. You may opt for the Vitotrol 200 for the upstairs. The 200 will provide indoor feedback but not give you the same features as the Vitotrol 300.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • GordanGordan Member Posts: 891
    LLH with such a small heat loss?

    Chris, not sure if you caught the low heat loss - the design flow even at 20F dT would be well below the max that the heat exchanger can handle, let alone at 30F dT. And the head loss at 3.5 gpm is a tolerable 7 ft. It doesn't seem like hydraulic isolation would be required here.
  • ChrisChris Member Posts: 3,056
    Minimum Flow Rate

    Be apt to worry about maintaining minimum flow rate of 1.7 then max'ing out. That LLH is my air elimation and will also give me the best opportunity to see the coldest return boiler water temp. I also want my supply sensor in a good mass of blended water not in a tiny pipe or in the case of direct pipe not even used. Will it work without the LLH. It would but you would also not be able to use that bumblee in the delta-t mode if you direct piped it.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • GordanGordan Member Posts: 891
    Seems like it should work

    Air and dirt elimination are addressable separately.

    Regarding coldest return temps, a LLH (or a buffer with two sets of tappings) gives the best shot at it only when compared with lesser forms of hydraulic separation, but the absolute best chance at the lowest return temps comes from direct piping the return into the boiler. No way around that. The issues around using the system sensor are also only an issue if you're doing hydraulic separation rather than direct piping.

    Regarding using variable rate pumping, seems like the Bumblebee would ensure there's adequate flow through the boiler by keeping dT from getting too wide. And TRVs with bypass, as you suggested, would keep system flow unaffected by TRV action and completely under the discretion of the Bumblebee. But I'll tell you this, I think Taco missed the boat by not allowing min and max gpm to be directly settable in the pump controller - they already measure that info, and think about the peace of mind that this would provide for those who'd like to use this pump for what it's best at.
  • ChrisChris Member Posts: 3,056
    They Also Missed The Boat

    By not giving us 0-10DVC and a field adjustable start time. Out of the box that pump runs a full 1-1/2 minutes before it reacts. The VDT used only a 35 second delay time.

    I'm always up for a good adventure so I would apt to try it. Had a good conversation concerning using this pump as a boiler pump with someone in Viessmann engineering while over in Germany and it will do the job just don't think I'd give those reins to a homeowner unless they really understood the physics of what is going on.

    With HO's I feel it's safer and easier to give them the least possible way to get into trouble.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • SWEISWEI Member Posts: 7,356
    missed the boat for sure

    A 0-10V input would put them squarely ahead of Wilo and Grundfos.  Then there's the smaller smart circ we just can't seem to buy over here.  Wilo at least offers 0-10V and BACnet modules for their larger pumps.
  • GordanGordan Member Posts: 891
    Ah, but not a fixed 0-10V input

    If we're wishing for features, then the ability to set the target gpm corresponding to the lowest and highest control voltage would, IMO, make it TRULY useful. So you're not controlling the duty point in a way that ignores what's going on with the system.
  • ChrisChris Member Posts: 3,056
    Yes Sir

    How wonderful would it be to actually move gpm needed on a dime. The Bee concept with delta is great would be nice to have more flexibility in control and/or monitoring.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • SWEISWEI Member Posts: 7,356
    boiler pumps

    should be controlled by boiler controls IMO.  Most of the EU boilers have PWM outputs for just this purpose, but the corresponding pumps are OEM-only here as far as I have been able to determine.
  • smihailasmihaila Member Posts: 93
    ECM pumps

    -Going with those energy efficient pumps sounds like a super-great idea. I wasn't aware that in terms of technology such ECM pumps are considered newcomers in North-America. I can't find the Taco Bumble Bee at eComfort. I found only these models:

    Grundfos ALPHA 15-55F/LC,

    Grundfos ALPHA 15-55FR,

    Grundfos ALPHA 15-55SF, 

    Wilo Stratos ECO 16F,

    Grundfos MAGNA 32-60 E-Circulator

    The last 2 from the list (Stratos and Magna) are clearly ECM + adaptive. But not sure about those three Alpha models - the price seems very low when comparing to the last 2. The Grundfos models seem to have that LED display, looks very convenient and practical, whereas the Wilo has only a red dial. Or the appearances can be deceiving in this case?

    -Good idea as well about putting another variable/ECM pump also in the boiler circuit, and set at fixed speed.

    -I'll see if it's worth buying a second thermostat, Vitotrol 200, and KM Bus adapter for that. 
  • smihailasmihaila Member Posts: 93
    So a direct circuit is still preferred?

    Chirs and Gordan, thank you to both of you.

    So Gordan, you are basically saying that a LLH is best when you have more than 1 hydraulic circuit, or when there are very high (or very low) flow rates?

    I was having the same impression, that for such modest heating load it will be overkill? Do you think that due to the TRVs kicking in and out, there will be a large flow variation still warrantying the use of the LLH? If I go with LLH, there will be another $300 + another $200 for the temp sensor. Plus the need to install 2 pumps overall.

    I like on the other hand of having an water temp sensor in the water circuit...But doesn't the boiler have already one?

    The main question would be: just to be on the safe side, is the LLH a good option? Can it worsen the heat transfer than in a direct connection situation? Or by having it, the situation will be equal or even better? I wish to be sure that it won't affect the system in a slightly negative way.

    Thanks again.
  • smihailasmihaila Member Posts: 93

    That's actually a good observation, and another question that I wanted to ask is this: is the Vitodens 200 boiler able to output PWM and control PWM-enabled pumps?

    If yes, then the only factor making it not possible to use such config would be the fact that no PWM pumps are currently available here, in NA?

    Thank you.
  • smihailasmihaila Member Posts: 93
    Direct pump modulation via boiler

    Speaking of PWM pump control, I was also looking at the Rinnai condensing boilers.

    The Q85 series (i.e. ) mentions about this:

    "Fully modulating pump combines with stainless steel heat exchanger to make this one of the more efficient units available".

    Would that be a hint that they can drive PWM pumps?

    Also, their E75C ( ) or E110C series ( ) series seems interesting. Although not featuring a modulating pump, they come at least with integrated expansion tank and internal boiler pump.

    What do you think, going with Rinnai instead of Viessmann would be a downgrade?

    Thank you.
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