On Thu, 25 Dec 2003 00:54:05 +0000 (UTC), "Michael Chare"
wrote:

The heat loss from each radiator depends on its area. If you cant find this
in
a radiator catalogue or else where try a factor of 170 Btu/sq ft /hour

It also depends on the type of radiator, single/double panel, fins or
not and the model.

You can't just pluck numbers out of the air -

I didn't I took it from a reference book, and I suggested using the figure as
the less preferred alternative.


It's very less preferred. If you compare a single panel with a
double convector (e.g. in Myson's Premier range) the range is 3:1.



BTUs are really a deprecated unit.

Still surprisinly common in the heating industry.

Mmm. One noted for its conservative ways. Many of its
practitioners do not seem to be able to able to do arithmetic anyway.

I recently helped a neighbour with selecting an installer for a
replacement heating system. It had been badly neglected over the
years, and one or two radiators had sprung a leak. The Glow Worm
boiler was at the end of its useful life (if it ever had one in the
first place. Essentially it was replace all the system except the
pipework.

We put together a requirements document to give to the contenders
including a number of points:

- Description of the house and exisitng system
- List of requirements for heating operation
- List of requirements for hot water, including number of bathrooms,
pattern of use.

we asked contenders to provide:

- References of installations that we could contact
- Details of proposed systems, vendors used
- Evidence that the proposed systems could meet the specifications.

The six responses made entertaining reading, two contenders having
decided not to quote.

Two of them totally ignored the requirements document and proposed a
fairly small combi boiler - 15lpm. This was totally inadequate for
the hot water needs and they hadn't bothered to check that the mains
cold supply is poor where we are. They had both proposed large
double convector radiators in places where it was not necessary.

Another two proposed a pressurised hot water cylinder, but didn't
check the mains supply. They did bother to do so form of heat loss
assessment but one got the numbers wrong and proposed radiators in a
couple of rooms which were too large and the pipework would have been
inadequate to supply. They did get the boiler size about right
though.

The final two proposed a vented storage cylinder, with fast recovery,
larger than the existing one to meet the demand. They both presented
detailed heat loss figures for each room, a radiator proposal and
pointed out that in one large room the pipework would need to be
upgraded to support the radiator's requirements.
Both produced references.


In the end he selected one from the third group, the lower price of
the two, and because the person was able to do the work a little
earlier as well.
These two were not the most expensive nor were they the cheapest. The
most expensive proposal was in the first group and was the least
suitable. It was from a very well know national firm.




The new Potterton boiler
catalogue that I happen to have gives the boiler ouput in Btuh/hr with the kW
figure in brackets!!

I'm not surprised. Potterton has been noted for trading on its past
glories and producing junk products. A search through Google Groups
will reveal some of their more recent horror products.



Michael Chare


..andy

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