On Tue, 6 Jan 2004 00:00:50 +0000 (UTC),
wrote:
Hi all,
I've just had a new loft conversion done (well, it took about 12 months
what with the loft company taking forever to finish and the decorators
mucking around and eventually running off - fortunately with me owing
them money rather than the other way around).
Due to some bad advice and planning early on, there is no central heating
in the conversion (which is a bedroom with balcony ie lots of Velux, plus
a bathroom). The bathroom is all tiled, with electric underfloor heating
and an electric towel rail. The underfloor is nice as it keeps the tiles
from freezing the skin off the soles of your feet in winter, but the towel
rail is awful - takes ages to warm up and uses masses of electricity
without really heating the bathroom. Also the bedroom is very cold - the
old insulation in the original ceiling seems to be stopping any heat from
the rest of the house from making its way upstairs.
Ideally I'd like to extend the central heating upstairs, so I'd appreciate
any comments from those in the know. First here's a summary of the CH/HW
system:
Boiler is an old Potterton Netaheat 10-16 Mk II F, conventional gas-fired
boiler, pumped, with a 3-port motorised valve. There is a cold water tank
in the eaves space, a hot water cylinder in the airing closet on the 1st
floor next to the pump/3-port valve, and the header tank for the CH is in
the apex of the roof not next to the cold water tank. The CH is a
micro-bore system (with feed and return at opposite ends of the
radiators). I have no idea where the manifolds are located.
Based on the airing closet and loft location, the following scheme is
possible in terms of running pipes - I'd like to know if it's feasible
though:
- tap into the CH feed just after the 3-port valve
- take the pipe straight up about 2m to the ceiling of the 1st floor then
under the loft floor into the south eaves (about 3m), across the outside
of the loft room wall (another 3m) then enter the loft room
- install a long low radiator or two into the loft room along the 5m wall,
with return to the eaves space
- across the eaves again (8m) and into the bathroom, with a single
radiator
- back into the eaves (5m) under the floor (3m) and down to the original
junction (2m) for a total of about 30m extra pipework
- presumably a pressure relief valve would also be needed between the new
outbound and return pipes
Does this sound feasible? Effectively it creates a combination of single
pipe loop and micro-bore piping, but other than locating and hooking into
the split of the hot feed into the manifolds & the corresponding return is
there anything else I can do?
It's a bad idea to try to combine a one pipe and a two pipe system and
to be honest a one pipe system is not great to begin with.
Really, you should plan to add the new pieces in two pipe. This
doesn't need to be done in microbore or into a manfold. You need to
tap into the main (probably 22mm) run after the 3 port valve as you
say but then find the return.
Since the pipe runs are quite long, it is important to size the pipes
adequately - don't guess because you will be disappointed if you make
them too small.
There is a note on how to do this at
http://www.cda.org.uk/megab2/build/Pub150%20UKCB.pdf
You need to size the radiators to meet the heat loss and then the flow
rate required and pipe size are determined from this. Again, do do
the proper heat loss calculations using one of the radiator company's
programs - don't guess or you may have another disappointment like the
towel rail.
As the loft will get the freshest hot water,
will the returning water still be warm enough to heat the rest of the rads
(there are 12 existing radiators at the moment)?
The number of radiators is irrelevant. What matters is their heat
output. You can get these figures by measuring them and referring to
manufacturer data sheets. On a conventional boiler such as you
have, the actual outputs will be 89% of the numbers in the table
because the temperature is lower than that used for testing them.
The eaves spaces are
uninsulated (well the floor and walls of the eaves are but the roof is
just the back of the tiles) - would the CH piping need to be insulated to
retain the heat or is that overkill?
Ideally the pipes should be run on the inside of the insulation.
However, if you have to run them outside the insulation, then they
must be insulated with pipe insulation of at least the pipe diameter
thick - i.e. the total insulated size of a 22mm pipe becomes 66mm.
Alternatively I could install a new 2-port valve on the Ch side of the
3-port valve, to split the CH system into two separate circuits - one for
the existing house and another just for the loft.
You could do that, but it might need more work on the rest of the
system to convert it to use entirely two port valves. If you look on
Honeywell's web site it is called an S-plan plus system then. You
could just zone it off with a two port valve, but then the loft
heating is at the mercy of the rest of the house if you see what I
mean.
This way the loft
circuit would just have the loft radiators on it, and a separate
thermostat could be used so that the two zones are independently
regulated. This would require a more complicated control system than the
current mechanical/thermostatic one though.
yes.
Does the pipework have to be copper, or can parts be plastic? Owing to the
spaces that need to be worked in, parts might be really difficult to work
in copper.
It can be in plastic if you like.
Is the existing pump likely to need to be replaced to handle the work of
pumping hot water up 2.3m above what it does currently?
Hard to say. The issue is delivering the volume of water at the
rate required - both will increase as a result of this addition.
Or is it ok since
the header tank is right at the top of the house ie way above the proposed
new loft radiators?
As long as you have about a metre of head of the tank above the top
radiator circulation should be OK. The issue is as above.
I haven't done any formal calculations on the boiler rating to see if it
has sufficient output to heat the new space but gut feel says its ok as it
can heat the original parts of the house pretty fast from cold; also the
new loft is well insulated so should retain its heat well if I can just
get it in there in the first place!
Don't work on gut feel. This is not a large boiler so again you may
be disappointed. On the other hand, it is probably due for
replacement and you could simply try it out and replace the boiler if
it proves to be inadequate.
I've read about using long low radiators which resemble standard skirting
boards but are metal and contain two pipes for feed and return, which I
could run along 5-10m of the room instead of using conventional radiators.
Any thoughts?
Myson make them among others. I've used them in a similar situation
to yours. I've also used long conventional radiators 300mm high.
You have to see whether you get enough heat output for your
requirements.
Thanks,
Zane.
..andy
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