Can two boilers share the same flue?

hambrook

Just moved into a new place that currently has a Johnson & Starley Brink 17D Warm Air heating system in a ground floor boiler room and an Andrew Water heater in an airing cupboard on first floor.

The warm air heating we are sticking with as the boiler was replaced 18 months ago.

The hot water heater is of age unknown, only 109 litres and not producing enough pressure in showers.

Am considering putting a Range Tribune 250L indirect pressurised cylinder and Worcester Greenstar 30CDi next to the boiler and am wondering if I can get the new boiler and the existing warm air boiler using the same flue that goes up through the house exiting out of the roof?

Pincher

The short answer is yes.

The problem is you probably have to replace the existing internal flue into one that is designed for sharing. Two boilers need more airflow, for a start. If the warm air system is not on, does the forced fan of the Worscester blow carbon monoxide into the house via the shared flue?

If you run the shower with only cold water, does it have enough pressure? If not, then it's not the water heater's fault. If you have good pressure, then sort out the water heater. Power flush the heat exchanger, but if it's more than ten years old, might as well get a new one that does not have a pilot light (but will need a mains power supply, circa 60W, for the spark plug.)

hambrook

Pincher wrote: »

The short answer is yes.

The problem is you probably have to replace the existing internal flue into one that is designed for sharing. Two boilers need more airflow, for a start. If the warm air system is not on, does the forced fan of the Worscester blow carbon monoxide into the house via the shared flue?

If you run the shower with only cold water, does it have enough pressure? If not, then it's not the water heater's fault. If you have good pressure, then sort out the water heater. Power flush the heat exchanger, but if it's more than ten years old, might as well get a new one that does not have a pilot light (but will need a mains power supply, circa 60W, for the spark plug.)

Thanks for the reply. I think it's a combination of gravity fed water heater providing not enough pressure and all pipe work being 15mm apart from tank to cylinder which is 22m. But then there is a LONG run of 15 mm to the showers from the cylinder (10 - 15 meters). Hence my intention to forget this water heater in a 1st floor airing cupboard and go with a new pressurised cylinder near the mains water in and 22mm pipe from stop !!!! to the cylinder and then 22mm up to the loft to join onto the existing 15mm just above the showers.

Back to the flue issue then, so can this shared flu be retro fitted as a liner in an existing flue or do you rip the whole thing out and start again? Keep in mind the boilers are on ground floor and this is a 2 storey house.

gas4you

All room sealed appliances must have their own flues intact. As the 30CDi is room sealed then in answer to your question, no.

The only exception will be if they are allowed by manufacturers instructions to be fitted to a 'U' duct or 'SE' duct.

Pincher

There are flue systems designed for boilers from multiple apartments in a stack, but it's for purpose built developments. Where there's a will, there's a way,
it's just a matter of finding a specialist willing to do it.
I doubt it will save time and money, though.

For a house with external walls, there are externally mounted boilers and water heaters. You can lift the floorboards and run 22mm pipes fairly easily, too.

bengasman

Sometimes you can share the flues, sometimes not.
Combining an open flue, and a fanned flue would not be my first choice.
On top of that, a 30 kw boiler to heat up a cylinder is not a good idea either.