Boiler options - Ideal, Worcester Bosch or Viessmann?

[aval0n]

Apologies for hijacking Gizmo's thread but I'm in a similar situation and so thought it best to add a reply here rather than create an entirely new thread.

Here's my current system:

• Baxi System 100 HE Plus 22kW boiler (just over 17 years old and on its last legs)
• Megaflo 170l unvented hot water cylinder
• S plan with 2 zones
• Drayton Wiser wireless thermostat (supports OpenTherm)
• 11 panel radiators + 2 towel rads
• All panel rads (except for one) are connected to the system via JG Speedfit 10mm plastic pipe (I know...)

I'm not a fan of combis and the Megaflo tank is working fine, so am looking to replace the Baxi with another system boiler. The main priorities for me are decent warranty, quietness (boiler is located in the kitchen) and OpenTherm support. Unfortunately the latter seems to limit my options somewhat. I've noticed that the Baxi cycles quite a lot unless the outside temperature is very low, so 22kW is probably more than the house needs (17 year old 3 bed end of terrace), however it does heat the 170l tank in about 30 minutes, which is nice.

Based on my own research, reading through the forum and the replies in this thread the boilers on my list are currently:

• Intergas HRE 18kW (or maybe 24?) SB
• Viessmann VITODENS 100-W 19kW
  
• Vokera Unica MAX S 20kW

To be completely honest I'd never heard of Vokera until I started reading vulcancontinental's posts, but having watched a couple of his videos and read the specs they sound pretty decent. However I can't seem to find a noise level quoted anywhere...

Any thoughts and advice would be much appreciated.

 

[vulcancontinental]

Apologies for hijacking Gizmo's thread but I'm in a similar situation and so thought it best to add a reply here rather than create an entirely new thread.

Here's my current system:

• Baxi System 100 HE Plus 22kW boiler (just over 17 years old and on its last legs)
• Megaflo 170l unvented hot water cylinder
• S plan with 2 zones
• Drayton Wiser wireless thermostat (supports OpenTherm)
• 11 panel radiators + 2 towel rads
• All panel rads (except for one) are connected to the system via JG Speedfit 10mm plastic pipe (I know...)

I'm not a fan of combis and the Megaflo tank is working fine, so am looking to replace the Baxi with another system boiler. The main priorities for me are decent warranty, quietness (boiler is located in the kitchen) and OpenTherm support. Unfortunately the latter seems to limit my options somewhat. I've noticed that the Baxi cycles quite a lot unless the outside temperature is very low, so 22kW is probably more than the house needs (17 year old 3 bed end of terrace), however it does heat the 170l tank in about 30 minutes, which is nice.

Based on my own research, reading through the forum and the replies in this thread the boilers on my list are currently:

• Intergas HRE 18kW (or maybe 24?) SB
• Viessmann VITODENS 100-W 19kW
  
• Vokera Unica MAX S 20kW

To be completely honest I'd never heard of Vokera until I started reading vulcancontinental's posts, but having watched a couple of his videos and read the specs they sound pretty decent. However I can't seem to find a noise level quoted anywhere...

Any thoughts and advice would be much appreciated.

The ErP energy label has the sound level

 

[Mottie]

I'm no heating expert but 22kw seems a lot for what you have.

 

[aval0n]

The ErP energy label has the sound level

Thanks, I didn't think to look there! The Intergas HRE 18 SB is rated at 45dB, which is a fair bit lower than the 50dB for the Unica MAX S 20. Not sure how much different it would be in real world conditions though...

 

[vulcancontinental]

Thanks, I didn't think to look there! The Intergas HRE 18 SB is rated at 45dB, which is a fair bit lower than the 50dB for the Unica MAX S 20. Not sure how much different it would be in real world conditions though...

I can't help as I'm partially deaf but db is not a linear scale (I think logarithmic)

 

[aval0n]

Yes, dB is a log scale, so 3dB is equal to doubling the sound intensity. However, apparently a 10dB increase is required for it to be perceived as twice as loud though...

@vulcancontinental, sent you a PM. Thanks!

 

[oldbutnotdead]

Can't remember the quoted numbers on my Intergas Rapid 32 but in heating mode it is very quiet. Gets a bit noisier running dhw at full bore but doesn't worry the cat (her dishes are on the worktop just below it) and you can have a conversation next to it without changing voice level from it not running to running. Wouldn't have it in a bedroom though...

 

[aval0n]

Can't remember the quoted numbers on my Intergas Rapid 32 but in heating mode it is very quiet. Gets a bit noisier running dhw at full bore but doesn't worry the cat (her dishes are on the worktop just below it) and you can have a conversation next to it without changing voice level from it not running to running. Wouldn't have it in a bedroom though...

Just had a quick look and the Intergas Rapid 32 is listed as 50dB, which is the same as the the Unica MAX S 20, so this is helpful. Thanks!

 

[Screwdriva]

I'm probably too late to this but thought I'd share experiences of our Viessmann 200-W.

In short, we upgraded from a 5 year old 18 kW Greenstar Ri. Normally, we wouldn't have replaced a newer condensing boiler but we were installing a few retrofit efficiency upgrades simultaneously (wet UFH with XPS insulated boards, triple glazing, upsized T22 radiators) so we began the search for the most efficient gas boiler we could find and sold the old boiler on.

The V200-W is, hands down, the most efficient gas boiler sold in the UK for the following reasons:

- The best modulation ratio of any boiler - it can lower its output to ~2kW when the property achieves desired temperature. This is especially useful in smaller properties with larger emitter surface area (T22/ 23 radiators or underfloor heating).

- The best efficiency rating of 98% at full modulation

- Advanced weather compensation with zone specific curves and setback temperatures (this feature alone can save 15%).

- Hot Water heating at 50 degrees with tank thermostat with a weekly legionella cycle as a precaution.

It's also very quiet (inaudible at when the cabinet door is shut and barely audible when standing next to it) and comes with a 12 year warranty from Viessmann. We did some basic calculations when comparing to a quality Air Source Heat Pump. We assumed:

1) A price difference of ~£6K for the purchase of a German ASHP (Vaillant) after all government incentives.
2) A SCOP of 4 for the ASHP (optimistic) and a boiler efficiency of 95% (realistic)
3) Current price cap energy tariffs of .34p and 10.5p for gas and electricity respectively and
4) A total heating demand of 15K kWh

We would save £300 per annum with the heat pump. (In all likelihood, savings would be lower). It would take ~20 years to recover the added cost of the heat pump, assuming nothing went wrong. This reality, combined with supply issues, led us towards the V200-W, a decision we are very happy with. To date, just for DHW, we have saved ~25% gas YoY. We expect this to translate to household heating as well.

 

[JonathanM]

The best efficiency rating of 98% at full modulation

I think that 98% efficiency will only be if you fit weather compensation. The Viessman website says "ERP Efficiency 94% (Class A)" and then later "up to 98% efficient".

EDIT: It's actually very confusing, so please ignore what I said for the moment. For the 98% claim, they seem to be using a different efficiency criteria to ErP, which is the European standard. It will need a bit more checking.

 

[JonathanM]

So, as far as I can tell, the 98% claim seems to be based on a German standard (DIN), running the boiler at 40/30. I'd think most modern boilers would be 98% efficient when run at 40/30. In the Viessmann manual, I am finding it difficult to properly check the official figures.

By contrast, with the Alpha E-Tec R regular boiler I've been looking at, I found the efficiency figures to be a model of clarity. It is a much cheaper boiler, and the official ErP results from the manual are shown below. This is the ErP low temperature regime, and it may differ to the German one.

At 30% of rated heat output and low temperature regime (**), η1, 97.5 %

EDIT: on the same basis as above, the E-Tec system boiler is 97.7% efficient.

 

[Screwdriva]

Thanks for clarifying - I assumed 95% efficiency for the above calculation. And you kinda have to fit weather comp with the V200-W as it doesn't suggest or require any room influence (thermostats), another area of savings.

Any idea what the Alpha's modulation ratio and minimum output is? Can it charge the DHW cylinder at 50 degrees?

 

[JonathanM]

Thanks for clarifying. Any idea what the Alpha's modulation ratio and minimum output is?

Nowhere near as good! 4.3KW, and variable modulation ratio depending on which boiler, but the best is 7.5:1

EDIT: It would definitely be nice to have 1.9KW in terms of comfort, but in terms of efficiency the gains of extreme modulation are disputed. Viessmann did produce this graph which shows good gains. I don't know if you've seen it. It's quite confusing, but you want the gross efficiency figure on the right.

 

[JonathanM]

Can it charge the DHW cylinder at 50 degrees?

I'm not sure exactly what this is. Are you talking about when you have the weather compensation, and the central heating water is at low flow temperature, but it can still heat the cylinder to a higher temperature? The Alpha can do that with a bit of extra wiring. But it doesn't seem to have an automatic legionella disinfection.

I'm pretty sure the Alpha is nowhere near as reliable as the Viessmann. That's what surveys seem to suggest. And the 200-W is cutting edge.

 

[Screwdriva]

I'm pretty sure the Alpha is nowhere near as reliable as the Viessmann. That's what surveys seem to suggest. And the 200-W is cutting edge.

Jury is still out on reliability as it's only been 9 months since installation but I have to say I have to share that I've observed the boiler run at 10% modulation when using the UFH, during which time our gas consumption was surprisingly low for the amount of heat that was being emitted. It felt like we may be able to heat the entire property using ground floor UFH on all but the coldest of days. Fingers crossed, as this would mean a much higher % saving.

The 200-W is the only gas boiler sold in both UK and DE markets (the 050 and 100 are scaled down UK market only models). Apparently, the 300-W is even more advanced and borders on science fiction!

I'm not sure exactly what this is. Are you talking about when you have the weather compensation, and the central heating water is at low flow temperature, but it can still heat the cylinder to a higher temperature? The Alpha can do that with a bit of extra wiring. But it doesn't seem to have an automatic legionella disinfection.

Yes, DHW cylinder temperature target set at 50 degrees daily with a weekly legionella cycle (similar to a heat pump). All out of the box.