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  • Central heating / radiators advice needed please!
  • dirtbiker100
    Free Member

    My new house has microbores (8mm) feeding all the radiators in the house. Which is ok for most as they come off a 15mm pipe fairly close (1-2m away) to the rads themselves. But my main bedroom and lounge are fed off one microbore pipe.

    The drawing below might show better detail but the feed pipe comes from the boiler in 22mm, splits into two 15mm pipes. One going to 2 small upstairs rads and one that hits a t-junction splitting into two 8mm microbore pipes. One way goes 1-2m into a small bedroom (2.75m x 2.4m) rad and the other way travels 3.6m where it splits off into a large bedroom (3.5m x 3.5m) rad while the rest carries straight on to the corner of the room down the lounge wall (2.35m high) and along into a rad big enough to heat the lounge – 6.5m x 3.5m.

    Total distance travelled since leaving the 15mm = 8.35m in which it needs to heat the bedroom at the lounge.

    Do I need to change it to 15mm in order for both rooms to be heated sufficiently? I have cavity wall and plenty of loft insulation too.
    Some have said that the long microbore pipes will not heat the rooms comfortably while my dad who is helping with DIY seems adamant that it's fine.

    Anyone have any ideas?

    http://img.photobucket.com/albums/v514/Anoobis/9_0069.png

    sidewinder
    Free Member

    The problem is the pipework is undersized, as a rule of thumb work on 1,000 btu's per 1mm of pipework bore,in your case 8,000 btu's go to a heating supplier (plumb center,pts etc) and get a radiator price guide with heat outputs combined ,it doesn,t matter if theyre not the same make of radiator you can then work out what your heat output is per radiator, given the pipe run lengths heat loss per run is not too much of an issue hope this helps ?

    Bear
    Free Member

    As a rule of thumb 15mm pipe will carry 6kW of heating load, 22mm 13kW. Obviously this is dependant on length of run, number of fittings etc. Unfortunately I haven't got my books with me for the figures for microbore as I don't use it personally.

    From the sounds of things this is an existing system? If so the best way to prove if the heating is working is to balance the system. Turn all thermostats up, and measure the temperature difference acrosss the flow and return pipework as it enters the radiator. Noting both flow and return tamperatures. You should be aiming for an 11deg. C temp difference across the pipes. If the difference is too high, then the radiator is not being supplied with enough water, too low and the flow rate is too high. To adjust this use the balancing / lockshield valve on each radiator. This is the valve with a plastic top that you can't turn. Remove the top and use a spanner on the spindle. Most of the adjustment will come on the first 1 or 2 turns. You need to make small adjustemnts, wait 20 mins or so and then re-check temperatures, you will probably need to make several adjustments to get it right. Sometimes on big systems and where the pipework is not very well sized it can take a whole day!

    This is the first thing I would try before going to the expense and hassle of changing the pipes. I suspect your system will work but will require careful balancing.

    I've a simple spreadsheet that I use for calculating pipe sizes for heating systems, need an isometric drawing of the system will lengths of runs, and any elbows bends and tess fitted.

    Any further queries mail me at timATj-twren.eclipse.co.uk

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    spooky_b329
    Full Member

    From an inexperienced point of view, why have a double rad in the bedroom, and a smaller single rad in the lounge which is getting close to twice the size of the bedroom? You would normally have the bedroom cooler anyway, plus heat rises.

    I see you have a chimney so possibly a stove for heating, but surely it would be good to plan for the rad to be able to cope with heating the room by itself?

    (I assumed you were putting a new system into a new house but re-reading the post its obvious its existing)

    dirtbiker100
    Free Member

    Spooky,
    Forgot to mention that I am at least planning on swapping the rads around so the double is in the lounge. There is going to be a new gas fire in the lounge fireplace but i'd prefer to keep use to a minimum really.

    Just bought the house (built around 1950, ex-council) and while putting in a new boiler the gas guy commented on the radiator situation.

    Thanks very much bear and sidewiinder. That gives me something to work on.
    8mm supplies 8,000 btu and I know I need around 10,000 for the lounge…

    Bear
    Free Member

    you sure you need that much for the lounge?

    that's nearly 3kW.

    Heat loss the building, loads of free bits of software available, if not I'll give it a go for you. Mail me if you want me to.

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