Is this the right boiler for me?

Frog_Prince

I have a 70 sq m, 2 bedroom flat just outside the M25. It has 1 bathroom with a tub and shower, 1 en-suite shower stall and 7 radiators. It is the middle flat on the middle floor of the block. 

It was kitted with a Potterton Powermax 155x at construction in 2002, meant to provide hot water at mains pressure. There is a flue in the ceiling void. The distance between the internal wall behind the boiler and the flue outlet in the external wall is 7-8 metres. The external wall cannot be altered.

The Powermax needs replacing, preferably by something with similar performance. My preference is a storage combi like a Viessmann 111W, but an engineer who visited last week thinks the only manufacturer that would supply a long enough flue is Worcester Bosch, and the most suitable Worcester Bosch is a Greenstar 8000 Life 30kw system boiler and a cylinder.

After installation of the new flue, the ceiling will be repaired with the addition of flue inspection hatches which are necessary wherever there is a join, according to the engineer.

The engineer’s estimate is £4,800 including new condensate pipe behind kitchen units, flushing, commissioning and VAT.

Is this the right boiler at the right price?

ThisIsWeird

Please check the model of that W-B boiler - it cannot be 'system' and 30kW.

Frog_Prince

The snip below is from the estimate. You can look up the specs here: https://www.worcester-bosch.co.uk/products/boilers/directory/greenstar-8000-life-system

Estimate to replace existing thermal heat store with  20.0% S      4,025.00 
Worcester Greenstar 8000 life 30kw system boiler.     

FreeBear

Frog_Prince said:

I have a 70 sq m, 2 bedroom flat just outside the M25. It has 1 bathroom with a tub and shower, 1 en-suite shower stall and 7 radiators. It is the middle flat on the middle floor of the block. 

It was kitted with a Potterton Powermax 155x at construction in 2002, meant to provide hot water at mains pressure. There is a flue in the ceiling void. The distance between the internal wall behind the boiler and the flue outlet in the external wall is 7-8 metres. The external wall cannot be altered.

The Powermax needs replacing, preferably by something with similar performance. My preference is a storage combi like a Viessmann 111W, but an engineer who visited last week thinks the only manufacturer that would supply a long enough flue is Worcester Bosch, and the most suitable Worcester Bosch is a Greenstar 8000 Life 30kw system boiler and a cylinder.

After installation of the new flue, the ceiling will be repaired with the addition of flue inspection hatches which are necessary wherever there is a join, according to the engineer.

The engineer’s estimate is £4,800 including new condensate pipe behind kitchen units, flushing, commissioning and VAT.

Is this the right boiler at the right price?

If you are set on a Viessmann boiler, I'd suggest contacting an engineer that has been trained on their products - https://www.viessmann.co.uk/en/installer-finder.html

Looking at this doc - https://viessmanndirect.co.uk/files/3c72d639-4428-4d52-a2fb-a7da00f36e93/Gas Condensing Boiler Flue Systems.pdf - The Vitodens range can be fitted with up to 20m of 60/100mm or 80/125mm flue (depending on boiler rating). Note, each 90 degree bend counts as 1m, so if you have lots of bends the flue length needs to be reduced.

Viessmann also do flue sections in different lengths (500mm, 1m, and 2m) - Pick the right sections, and you reduce the number of inspection hatches required.

Depending on the flow rate from your cold water tap, you might need a 30KW boiler or even a 35KW - I'm not convinced you need a store of hot water (the 111-w provides 47l). It is wasteful of gas keeping that little tank hot and it isn't going to provide hot water at a higher pressure than the cold supply.

I have the 050-W, and find it more than adequate for heating and hot water.

ThisIsWeird

Frog_Prince said:

The snip below is from the estimate. You can look up the specs here: https://www.worcester-bosch.co.uk/products/boilers/directory/greenstar-8000-life-system

Estimate to replace existing thermal heat store with  20.0% S      4,025.00 
Worcester Greenstar 8000 life 30kw system boiler.     

Thanks.

I don't understand the 30kW figure, unless it can instantly heat up DHW on demand.

Will your system have a small hot water storage cylinder?

FreeBear

ThisIsWeird said:

Frog_Prince said:

The snip below is from the estimate. You can look up the specs here: https://www.worcester-bosch.co.uk/products/boilers/directory/greenstar-8000-life-system

Estimate to replace existing thermal heat store with  20.0% S      4,025.00 
Worcester Greenstar 8000 life 30kw system boiler.     

Thanks.

I don't understand the 30kW figure, unless it can instantly heat up DHW on demand.

Will your system have a small hot water storage cylinder?

The Potterton Powermax 155x (the OP's current boiler) is a combi boiler with an internal hot water tank of some 100l. Very similar to the Viessman 111-W (but with just a 47l store). This type of boiler is designed for larger households where a traditional combi may struggle with peak DHW demand.

To replace this with a 30KW system boiler plus (presumably) an unvented hot water tank is just plain silly - No way would a 2 bed flat need that much energy for heating and hot water. 10-12KW would be more than adequate, ineed, my old (heat only) boiler was rated at ~13KW for a 3 bed semi.

Lorian

Somewhat In its defence though the Worcester 8000 has a modulation ratio of 1:10 which means it can fire as low as 3kW depending on demand.

In a flat I think I'd be looking for a straight combi boiler to save the space though.

ThisIsWeird

FreeBear said:

ThisIsWeird said:

Frog_Prince said:

The snip below is from the estimate. You can look up the specs here: https://www.worcester-bosch.co.uk/products/boilers/directory/greenstar-8000-life-system

Estimate to replace existing thermal heat store with  20.0% S      4,025.00 
Worcester Greenstar 8000 life 30kw system boiler.     

Thanks.

I don't understand the 30kW figure, unless it can instantly heat up DHW on demand.

Will your system have a small hot water storage cylinder?

The Potterton Powermax 155x (the OP's current boiler) is a combi boiler with an internal hot water tank of some 100l. Very similar to the Viessman 111-W (but with just a 47l store). This type of boiler is designed for larger households where a traditional combi may struggle with peak DHW demand.

To replace this with a 30KW system boiler plus (presumably) an unvented hot water tank is just plain silly - No way would a 2 bed flat need that much energy for heating and hot water. 10-12KW would be more than adequate, ineed, my old (heat only) boiler was rated at ~13KW for a 3 bed semi.

Thanks FreeBear - yes, something is wrong somewhere!

For example, that old PottPowermax (sil has one, so I'm familiar with them) is only rated at 15kW. Ratings approaching 30kW are only required for combis or very large houses with dozens of rads... And, they'll also almost certainly require a gas pipe upgrade.

I suspect it's an 'error', and the Viessman isn't really capable of 30kW.

F-Prince, how often will both bathroom/showers be used at the same time? Have you completely discounted having a combi?

FreeBear

ThisIsWeird said:

FreeBear said:

ThisIsWeird said:

Frog_Prince said:

The snip below is from the estimate. You can look up the specs here: https://www.worcester-bosch.co.uk/products/boilers/directory/greenstar-8000-life-system

Estimate to replace existing thermal heat store with  20.0% S      4,025.00 
Worcester Greenstar 8000 life 30kw system boiler.     

Thanks.

I don't understand the 30kW figure, unless it can instantly heat up DHW on demand.

Will your system have a small hot water storage cylinder?

The Potterton Powermax 155x (the OP's current boiler) is a combi boiler with an internal hot water tank of some 100l. Very similar to the Viessman 111-W (but with just a 47l store). This type of boiler is designed for larger households where a traditional combi may struggle with peak DHW demand.

To replace this with a 30KW system boiler plus (presumably) an unvented hot water tank is just plain silly - No way would a 2 bed flat need that much energy for heating and hot water. 10-12KW would be more than adequate, ineed, my old (heat only) boiler was rated at ~13KW for a 3 bed semi.

I suspect it's an 'error', and the Viessman isn't really capable of 30kW.

The Viessmann Vitodens 111-W is a combi, just like the Potterton, so will hit 30KW when heating the DHW. It will also modulate down to ~3KW for central heating.

ThisIsWeird

FreeBear said:

ThisIsWeird said:

FreeBear said:

ThisIsWeird said:

Frog_Prince said:

The snip below is from the estimate. You can look up the specs here: https://www.worcester-bosch.co.uk/products/boilers/directory/greenstar-8000-life-system

Estimate to replace existing thermal heat store with  20.0% S      4,025.00 
Worcester Greenstar 8000 life 30kw system boiler.     

Thanks.

I don't understand the 30kW figure, unless it can instantly heat up DHW on demand.

Will your system have a small hot water storage cylinder?

The Potterton Powermax 155x (the OP's current boiler) is a combi boiler with an internal hot water tank of some 100l. Very similar to the Viessman 111-W (but with just a 47l store). This type of boiler is designed for larger households where a traditional combi may struggle with peak DHW demand.

To replace this with a 30KW system boiler plus (presumably) an unvented hot water tank is just plain silly - No way would a 2 bed flat need that much energy for heating and hot water. 10-12KW would be more than adequate, ineed, my old (heat only) boiler was rated at ~13KW for a 3 bed semi.

I suspect it's an 'error', and the Viessman isn't really capable of 30kW.

The Viessmann Vitodens 111-W is a combi, just like the Potterton, so will hit 30KW when heating the DHW. It will also modulate down to ~3KW for central heating.

I was referring to the WB 'Greenstar 8000 Life 30kW System' boiler.

Albermarle

FreeBear said:

ThisIsWeird said:

Frog_Prince said:

The snip below is from the estimate. You can look up the specs here: https://www.worcester-bosch.co.uk/products/boilers/directory/greenstar-8000-life-system

Estimate to replace existing thermal heat store with  20.0% S      4,025.00 
Worcester Greenstar 8000 life 30kw system boiler.     

Thanks.

I don't understand the 30kW figure, unless it can instantly heat up DHW on demand.

Will your system have a small hot water storage cylinder?

The Potterton Powermax 155x (the OP's current boiler) is a combi boiler with an internal hot water tank of some 100l. Very similar to the Viessman 111-W (but with just a 47l store). This type of boiler is designed for larger households where a traditional combi may struggle with peak DHW demand.

To replace this with a 30KW system boiler plus (presumably) an unvented hot water tank is just plain silly - No way would a 2 bed flat need that much energy for heating and hot water. 10-12KW would be more than adequate, ineed, my old (heat only) boiler was rated at ~13KW for a 3 bed semi.

I  have a four bedroom, three bathroom older  house, with 13 radiators and a 18 KW boiler. It seems to manage fine, even when everybody is at home and it is starting up from cold, and all radiators are on. 

F-Prince, how often will both bathroom/showers be used at the same time? Have you completely discounted having a combi?
My own experience is that even with an unvented hot water tank under mains pressure, it is not guaranteed you can have two or three showers running at the same time without issues. Although maybe my system is not set up quite right.