Which boiler for our house?

[dormermike]

Yes plenty of hot water on tap with its inbuilt hot cylinder. Told it’s easy to service as it well designed.

Great to hear. I'm getting one fitted soon.

 

[Madrab]

Storage combi's - they're ok until the storage capacity is used up then they'll click over to a normal combi outputs and behaviours.

They seem to have relatively good outputs on paper as a combi but rated @ 30Deg rise (DeltaT) and not @ 35deg like other boilers specs.

 

[dormermike]

Storage combi's - they're ok until the storage capacity is used up then they'll click over to a normal combi outputs and behaviours.

They seem to have relatively good outputs on paper as a combi but rated @ 30Deg rise (DeltaT) and not @ 35deg like other boilers specs.

Thanks, interesting. I've had several plumbers/heating engineers out and can never seem to get any sort of technical detail like you've just provided. When you say 35deg like other boilers, do you mean other combi boilers specifically? I like a hot shower. Does this mean if my incoming water is 10c the 111-w can only raise the temp to 40c?

Also with its 40L tank, at a incoming flow rate of 16lpm, does that mean I get only 2 minutes of hot water before.. errr.. what happens when the tank empties? Does it take long to replenish?

 

[Madrab]

Thanks, interesting. I've had several plumbers/heating engineers out and can never seem to get any sort of technical detail like you've just provided. When you say 35deg like other boilers, do you mean other combi boilers specifically? I like a hot shower. Does this mean if my incoming water is 10c the 111-w can only raise the temp to 40c?

Simple to check the boiler's MI's and all the specs are in there -

Most other boiler manufacturers will quote on a 35Deg Delta - whereby a boiler a certain KW output, will deliver a certain amount of HW (L/Min) at a given temp rise, Viessmann use 30Deg K.

So the W-111 - Type B1LB - will deliver - 18L/Min @ 29.3Kw and 20L/Min @ 35kw from the storage cylinder (Loading Cyl) but once that stores used up (starts @ 46L (wall mounted internal) up to 170L (floor standing)), then it can drop more towards standard combi outputs.

The benefit over standard combi's though is their ability to service more than one HW output at a time without serious impact to each, given it's an unvented (UV) storage system. They are a bit of a half way house depending on how they are utilised with higher capabilities/capacities than a combi but not reaching the same types of output as dedicated UV storage.

 

[dormermike]

Simple to check the boiler's MI's and all the specs are in there -

Most other boiler manufacturers will quote on a 35Deg Delta - whereby a boiler a certain KW output, will deliver a certain amount of HW (L/Min) at a given temp rise, Viessmann use 30Deg K.

So the W-111 - Type B1LB - will deliver - 18L/Min @ 29.3Kw and 20L/Min @ 35kw from the storage cylinder (Loading Cyl) but once that stores used up (starts @ 46L (wall mounted internal) up to 170L (floor standing)), then it can drop more towards standard combi outputs.

The benefit over standard combi's though is their ability to service more than one HW output at a time without serious impact to each, given it's an unvented (UV) storage system. They are a bit of a half way house depending on how they are utilised with higher capabilities/capacities than a combi but not reaching the same types of output as dedicated UV storage.

Thanks. Its the 32kw i was looking at. The modulation looks good for heating and is the same on both the 24kw and 32kw, but the DHW performance of the 32 is better.

DHW flow rate
35˚C temp. rise (cont) l/min 18.1
30K rise (EN13203-1) l/min 21.2

So 35c at 18.1 lpm. How long does that translate to in the real world for a shower? Could i still have a hot shower? 35c doesn't seem like much, but my incoming flow rate is only 16-18lpm anyway, and there is cold water to mix with that, so i'm guessing the boiler can do a higher temp than 35c?

I don't doubt a unvented would be better but unfortunately i don't have the space. I have tanks at the moment, and need those to be removed, so the 111w seems a good compromise. Later, I think, if I find the space, I could add an additional unvented cylinder, presumably, just as with a regular combi.

 

[Madrab]

Don't forget, these figures are ideal - @ peak dynamic flow rates and pressures. If your mains can't sustain those kinds of figures then you won't see those kind of figures @ the outlets, regardless of what system you have.

I believe the way they look at it is ... though I am not sure how reflective of real world usage it is, the way the boiler handles the HW delivery and recovery - the 46L cylinder can be the equivalent of around double that of HW at equivalent shower temps ~ 38deg.

To put that into perspective - a 14L per min shower would use that up in around 10mins @ a 2/3rds mix - Obviously if the HW mix is higher then that timescale would drop before its used up and switches. More than one shower or HW outlet running and obviously it would be used faster.

The way I would describe it is - A combi with more than one HW outlet at the time has to be managed quite specifically, with a storage combi then more than one HW outlet (edit) can be used at the same time but still has to be managed but there is more flexibility. An unvented cylinder doesn't need to be managed - stored volume not withstanding. All are also very sensitive to dynamic mains pressure and flow.

 

[dormermike]

Great explanation, thank you for taking the time.