On 12/01/2019 09:28, wrote:
On 12/01/2019 08:56, tim... wrote:


wrote in message
...
On 11/01/2019 21:30, John Rumm wrote:
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as

Indeed...

1) it makes the radiators too hot to touch
2) basic thermodynamics suggest that a better temperature profile
will result from having the radiators at the lower temperate for
longer period than a higher temperature for a shorter period

It might be required in particularly cold weather, but most of the
time you will be able to use less.


I tried to explain this but was met with

"The recommended temperature is required for the condenser to have
any effect"

You will most heat recovered from the condenser when the return
temperature is below about 54 degrees (the dew point of the flue
gasses).

and the completely bogus "the temperature of the water in the
radiators is set by the TRVs not the boiler temp.Â* I couldn't
persuade the guy that he was taking bollox, he played the "I'm the
experience heating engineer card and I know better than you" card.
****

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do

I have weather compensation on mine, and so it chooses its own
temperature based on the outside temp. Basically that means its runs
as cool as it thinks it can get away with and still be able to reach
the target set point temperature in a reasonable amount of time.
(the relationship is set by choosing a mapping curve that reflects
the rate of heat loss of the building).

Currently the external temp is 6.5 deg C, and the flow temp is
running at 54 deg. If it were to go well below 0, then it might push
the flow temp up into the 70s. When its milder it might run flow
temps down in the 40s.


I thought the advice was to heat DHW to 60 degrees to avoid the risk
of legionella, and that's not going to happen if the boiler's running
at a lower temp.

the temp for the hot water and CH system are set independently in a combi



I was replying to John (but had forgotten about combis)

The combi won't usually get it any hotter (since flow rate and
temperature are mutually exclusive), but the again there is no
significant store of water to act as a breeding ground either.


--
Cheers,

John.

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