Back boiler replacement

ed110220

After living with our old back boiler for two years I'm thinking of getting it replaced and would appreciate some advice on a value for money replacement.

Initially we were intending to keep the existing Baxi Bermuda SL3 as the gas engineer advised to as in his opinion they are reliable and tend to be trouble free. Also we use less than 10 000 kWh of gas per year.

This is all well and good, but being non-room sealed it needs a 1000 mm^3 vent to the outside in the living room through which a large amount of cold air is sucked in winter making the whole downstairs draughty. I've done a lot of insulation and draught proofing and this has really helped upstairs but I feel it's all negated downstairs by having a gaping hole in the wall.

At the moment the SL3 heats hot water in a vented cylinder in the airing cupboard and runs an 8 mm microbore central heating system. I have replaced the oldest, non-finned radiators and fitted TRVs to all radiators (there were none originally). The CH appears to work fine and I'm reluctant to change it for money reasons and the difficulty/disruption involved. I'm aware standard sized pipes are generally preferred but the house construction would make them difficult to run. The ground floor is concrete and the first floor is supported by steel I-beams that cannot be drilled or notched but there is just enough room between them and the ceiling for the 8 mm pipes.

So for a replacement boiler does sticking with a heat-only boiler make things a lot simpler in fitting it into the existing system, especially if it can be sited near the existing pipework? I was thinking of one of the Remeha Avanta heat-only range, say the 12V or 15V (the Baxi is about 15 kW).

sk240

1000mm2, that seems very excessive.
I had a back boiler too for a good 10 years, and only had a large ish air brick in the room.
As the plumber said, they are bullet proof, and are cheap to repair if the do go wrong.
However at only 65% effieciency are not great.
Only you can decide if a £1500 - 2K investment is worth it or not.
Payback it probably a good number of years
PS i hope you have a carbom monixide alarm

ed110220

sk240 wrote: »

1000mm2, that seems very excessive.
I had a back boiler too for a good 10 years, and only had a large ish air brick in the room.
As the plumber said, they are bullet proof, and are cheap to repair if the do go wrong.
However at only 65% effieciency are not great.
Only you can decide if a £1500 - 2K investment is worth it or not.
Payback it probably a good number of years
PS i hope you have a carbom monixide alarm

Hi, thanks for the reply. Yes, we do have a CO alarm. I calculate that we'll save about 33% on our gas bill, which at about 10 000 kWh will be about £200 a year at current prices. However the bigger reason is comfort and not having to suffer a cold draught.

1000 mm^3 is not that large, it's only the equivalent of a round hole 36 mm in diameter. The actual pipe through the wall is a lot bigger than that, but I think the figure refers to the area of the actual holes in the grille - the whole grille is about 150 x 150 mm. It's not huge, but in the context of draughts it's big.

Does anyone have an idea of how much of a difference in cost and disruption sticking with a heat only boiler and the present cylinder over a combi makes? I've had both and don't have a strong preference either way.

ed110220

Sorry, the vent is 100 cm^3 which is 10 000 mm^3! It's one like this:-

To put that in context this is what one of the UK's leading experts on airtightness in buildings has to say:


For a typical semi-detached house, meeting the 0.6 ACH requirement of a PassivHaus would require an
effective leakage area of less than 0.01 m2
@50 Pa (i.e. a 10 cm x 10 cm hole) which might seem like a large
and unlikely value. However, if we recast the hole as a crack formed around the perimeter of the building,
then the width of the crack would be 0.25 mm thick (for a house with a 10 m x 10 m floor area). Since cracks
can commonly occur around doors and windows, this illustrates the attention to detail that needs to be given to
achieve a sufficiently airtight building.

http://emps.exeter.ac.uk/media/universityofexeter/emps/research/cee/lchsmodule1notes/Air_Leakage_Testing.pdf

Obviously I'm not going to achieve Passivhaus standards in a 1940s refurb, but just that one vent leaks as much air as is allowed for a whole house of the highest standard!

diywhynot

Get a RGI in to conduct site survey and discuss your requirements.

ed110220

diywhynot wrote: »

Get a RGI in to conduct site survey and discuss your requirements.

That'll be my next step, but I'd like to know a bit more before I do.