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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthorandykent
    • CommentTimeMar 6th 2018
    My house has two (gas) boilers from the days when it was divided into two flats. One is very old and should be replaced asap. What are the relative merits of keeping two boilers or reconfiguring everything into one?

    My instinct had been telling me to move to a single unit with a storage tank for renewables and a system of room stats, but I am now questioning that. It's a town house and the scope for bringing in renewables is pretty limited, it has been useful to be able to time the upstairs and downstairs separately, presumably the room stat system would work the same either way, and I'm considering downsizing the house anyway so am wary of taking on significant ancillary works unless I decide to stay.

    The older boiler is developing an accelerating leak which is beyond economical repair so I need to make a quick decision!
    Go for one boiler, it will be cheaper to get one larger boiler than 2 smaller ones - not to mention double the maintenance down the line. If renewables are limited then (eventually) go for PV and install a bog standard combi boiler to cover CH and DHW. If you have 2 CH systems currently then it will be a simple matter to have 2 zones aided and abetted by TRVs on all the rads.

    Oh and if you are thinking of selling to downsize then a combie boiler is what the market looks for and any heating system that smacks of complications beyond the norm is a sales deterrent.
    • CommentAuthorandykent
    • CommentTimeMar 6th 2018
    Further info: both boilers are combis and the newer one won't need replacing for a few years yet.
    The long-term issue is controllability, efficiency (I've heard boilers are more efficient when they run flat out) and whether solar thermal or (less likely) a wood burner with back boiler will ever be incorporated.
    Will the combi that is in good condition manage the whole house - if so ditch the duff one and couple the systems by having 2 zones. I would not suggest a wood burner with a back boiler because there is always a conflict between the space heating demands and the requirements of the back boiler. Also the expense of the installation of a back boiler system would IMO be difficult to justify especially if you are buying in the wood and given that it is a town house you probably don't have storage space to properly season wood for 2 years to ensure efficient burning with minimum pollution. If you want a wood burner get a space heater probably sub 5kW
    We've gone for split thermal stores/water heater (SunAmp) due to dead legs and distribution lengths. It made sense to have the heater close to the point of use, but that's only because we're at passivhaus levels of insulation and PHPP would 'punish' us for the heat loss from a long pipe rather than treat it as a useful gain.

    Having lived in an old uninsulated property with a bathroom a long way from the boiler, I can definitely say that the inefficiencies of dead legs can lead to a lot of water wastage (as you wait for the hot water to clear the length of the cooled water in the pipe), so worth taking into consideration the physical geometry of what you are trying to do.
    • CommentAuthorandykent
    • CommentTime5 hours ago edited
    I've now decided to go for a zoned control system such as the Honeywell Evohome - probably 7 or 8 zones.

    In the long term rationalising the system into to a single boiler would save on space, maintenance and capital costs. But are there reasons for sticking with two boilers even with the zoned control system?
    • CommentAuthortony
    • CommentTime5 hours ago
    If one boiler breaks down you still have heating
    • CommentTime2 hours ago edited
    I'd favour Peter's idea, if the single remaining boiler would keep the whole heated except for the relatively few coldest days when extra cardi(s) or elect convector(s) would fill the gap. Then uprate if and when it wears out or it becomes clear life depends on that or for resale purpose.
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