Combi boiler flue questions

[borka]

Hello

I am trying to replace my current gas boiler (Potterton) with a combi one (Worcester). Boiler is located in the middle of the flat on the upper floor. Two companies specializing in Worcester had a look and they both suggested to make a strictly vertical flue and for that they would need to make a new hole in a roof. I do not expect freeholder to be very excited about that, so I have done some research to see if current flue setup can be used. Current flue is about 7 meters long and it is 6cm in diameter and have 5 bends. According to Worcester manuals that would exceed maximum flue length. However, if I look at 8cm diameter flue, then maximum limit is much longer. For example for Greenstar 29CDi it is 18meters. Also it is possible to reduce the number of bends down to 3. So simple math indicates that by using flue 8cm in diameter, 7 meters long and 3 bends (add 2 meters each) I would get an equivalent of 13 meters flue, which would not exceed maximum length and would eliminate need for creating any new holes. So the questions are:

Is my conclusion valid or am I missing something?

 

[nysk2008]

Just take advise from the gas safe engineer you have obviously hired

 

[hammers4spanner]

Sounds like flues in voids if your in a flat so access panels galore

 

[glenno1]

Ask your plumber if it is possible to move the boiler to a more convenient place like an external wall

 

[chris watkins]

Hello

I am trying to replace my current gas boiler (Potterton) with a combi one (Worcester). Boiler is located in the middle of the flat on the upper floor. Two companies specializing in Worcester had a look and they both suggested to make a strictly vertical flue and for that they would need to make a new hole in a roof. I do not expect freeholder to be very excited about that, so I have done some research to see if current flue setup can be used. Current flue is about 7 meters long and it is 6cm in diameter and have 5 bends. According to Worcester manuals that would exceed maximum flue length. However, if I look at 8cm diameter flue, then maximum limit is much longer. For example for Greenstar 29CDi it is 18meters. Also it is possible to reduce the number of bends down to 3. So simple math indicates that by using flue 8cm in diameter, 7 meters long and 3 bends (add 2 meters each) I would get an equivalent of 13 meters flue, which would not exceed maximum length and would eliminate need for creating any new holes. So the questions are:

Is my conclusion valid or am I missing something?

Hi & welcome to the forum, unfortunately the only advice you will receive on hear is to go back to the GSR specialist companies & ask them to look at your suggestions & requote as required.
The flue system is such an important safety part of the boilers correct operation it can only be confirmed by a GSR engineer who is on site.
P.S. There are other makes which will different flueing lengths & sizes, sometimes it can pay not to specialize / stick to just one make of boiler.

 

[borka]

Thank you for your answers. Will see what are freeholder's thoughts on that.