I was browsing Ed Sirett's CH FAQ and followed the link to the
"Replacement Boiler Size Calculator" site:
http://www.idhee.org.uk/calculator.html

For my 95 m2, three-bedroom, one-floor, detached, L-shaped bungalow
in Scotland, it calculated 9.5kW, of which 2kW is for DHW (is that
sufficient? I have no idea how to calculate it).

I did the L in 2 rectangles and supplied the window sizes manually.
Where the smaller second rectangle meets the larger first I did not
count the wall (so it appears as a 3-wall room).

My current boiler is a 25-yo Potterton Netaheat. It says "10-16" on
it, which I presume is kW and the thermostat goes 1-5.

So, with these in mind, here are my questions:

1. Does the sizing calculator work with non-condensing boilers?

2. I see Ed says that the calculator tends to undersize. So, should I
aim to set the thermostat to around 2 or 3 (which, if linear, would be
about 12-13 kW, about 30% above the calculation)? Is the boiler
efficient at such a low setting?

Any answers will be most appreciated.

Kostas

On Sun, 08 Mar 2009 15:56:08 +0000, Kostas Kavoussanakis wrote:

I was browsing Ed Sirett's CH FAQ and followed the link to the
"Replacement Boiler Size Calculator" site:
http://www.idhee.org.uk/calculator.html

For my 95 m2, three-bedroom, one-floor, detached, L-shaped bungalow in
Scotland, it calculated 9.5kW, of which 2kW is for DHW (is that
sufficient? I have no idea how to calculate it).

IIRC the is no allowance for DHW in the new PART-L calculators. Anyway
some leeway is helpful.


I did the L in 2 rectangles and supplied the window sizes manually.
Where the smaller second rectangle meets the larger first I did not
count the wall (so it appears as a 3-wall room).

My current boiler is a 25-yo Potterton Netaheat. It says "10-16" on it,
which I presume is kW and the thermostat goes 1-5.

Yes the 10-16 is the output range which is a preset by the installer (by
adjusting the gas valve over the permitted range of pressures).



So, with these in mind, here are my questions:

1. Does the sizing calculator work with non-condensing boilers?
Yes, except that the SLIGHT undersizing makes me nervous of taking it too
seriously. It does not matter what sort of boiler you have this is a
calculation to determine how much heat is needed to heat the dwelling.



2. I see Ed says that the calculator tends to undersize. So, should I
aim to set the thermostat to around 2 or 3 (which, if linear, would be
about 12-13 kW, about 30% above the calculation)? Is the boiler
efficient at such a low setting?

The thermostat does not affect the power settings. If the boiler is
switching off an on from time to time during normal operation then you
can be sure that it is big enough. The fact that you have it at a
moderate setting means that you have enough radiator capacity.

So if you are replacing the boiler a unit with 12kW would be quite
comfortable. you might even go down a bit, but warm up time will
lengthen. Warm up time does not figure in the Calculator!



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

"Kostas Kavoussanakis" wrote


I was browsing Ed Sirett's CH FAQ and followed the link to the
"Replacement Boiler Size Calculator" site:
http://www.idhee.org.uk/calculator.html

For my 95 m2, three-bedroom, one-floor, detached, L-shaped bungalow in
Scotland, it calculated 9.5kW, of which 2kW is for DHW (is that
sufficient? I have no idea how to calculate it).

A lot will depend on the construction of the property, level of insulation,
outer skin brick/block configuration.
Also there should be some account taken of the temperature differential -
i.e. what is an acceptable "lowest outside temperature" in the area?
Maybe all of this is taken into account in the calculator.

I did a spreadsheet for my place detailing wall construction, insulation and
heat loss to adjacent rooms etc.
This I then compared to my father-in-law's rule of thumb figure of 1500 Btu
per 1000 cubic foot (0.053 Kw per cubic metre) and this was about 10% higher
than my calculated figure.

So, to get to the end of the ramblings, for approx boiler sizing your heat
requirement would be 0.053 x 95 x 2.4 (assumed ceiling height) = 12Kw.

Phil

On Mon, 09 Mar 2009 08:37:59 +0000, TheScullster wrote:

"Kostas Kavoussanakis" wrote


I was browsing Ed Sirett's CH FAQ and followed the link to the
"Replacement Boiler Size Calculator" site:
http://www.idhee.org.uk/calculator.html

For my 95 m2, three-bedroom, one-floor, detached, L-shaped bungalow in
Scotland, it calculated 9.5kW, of which 2kW is for DHW (is that
sufficient? I have no idea how to calculate it).

A lot will depend on the construction of the property, level of
insulation, outer skin brick/block configuration. Also there should be
some account taken of the temperature differential - i.e. what is an
acceptable "lowest outside temperature" in the area? Maybe all of this
is taken into account in the calculator.

Yes, crudely, by wall type and location.






--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

Thanks Ed and Phil,

On Sun, 08 Mar 2009 15:56:08 +0000, Kostas Kavoussanakis wrote:

2. I see Ed says that the calculator tends to undersize. So,
should I aim to set the thermostat to around 2 or 3 (which, if
linear, would be about 12-13 kW, about 30% above the calculation)?
Is the boiler efficient at such a low setting?

The thermostat does not affect the power settings. If the boiler is
switching off an on from time to time during normal operation then
you can be sure that it is big enough. The fact that you have it at
a moderate setting means that you have enough radiator capacity.

I am trying to tune the boiler thermostat for efficiency and learn a
few things in the process if I can. I took it down to 3 (a previous
thread had suggested that it should be all the way up, so as to heat
my cold lounge, but I could hear it short-cycling).

At the moment (~1.5 hours after it started this morning and still
trying to get the Honeywell CM907 to 21 deg) the boiler works for ~2
mins before its stat switches it off for ~3.5 mins; the pump is going
non-stop. Is that still classed as short-cycling?

Also, what is the effect of lowering the water temp? I presume that
the boiler will work for longer periods; does this automatically
suggest higher gas consumption?

Thanks,
Kostas

On Tue, 10 Mar 2009 08:08:15 +0000, Kostas Kavoussanakis wrote:

Thanks Ed and Phil,

On Sun, 08 Mar 2009 15:56:08 +0000, Kostas Kavoussanakis wrote:

2. I see Ed says that the calculator tends to undersize. So, should I
aim to set the thermostat to around 2 or 3 (which, if linear, would
be about 12-13 kW, about 30% above the calculation)? Is the boiler
efficient at such a low setting?

The thermostat does not affect the power settings. If the boiler is
switching off an on from time to time during normal operation then you
can be sure that it is big enough. The fact that you have it at a
moderate setting means that you have enough radiator capacity.

I am trying to tune the boiler thermostat for efficiency and learn a few
things in the process if I can. I took it down to 3 (a previous thread
had suggested that it should be all the way up, so as to heat my cold
lounge, but I could hear it short-cycling).

At the moment (~1.5 hours after it started this morning and still trying
to get the Honeywell CM907 to 21 deg) the boiler works for ~2 mins
before its stat switches it off for ~3.5 mins; the pump is going
non-stop. Is that still classed as short-cycling?

Also, what is the effect of lowering the water temp? I presume that the
boiler will work for longer periods; does this automatically suggest
higher gas consumption?

Thanks,
Kostas



I would say from what you have posted that the radiators have to be
hotter in your house to heat the cold lounge. (if that makes the rest of
the house too hot then those radiators need to have TRVs and/or have them
set lower).

Try a higher setting if the lounge is still cold add another radiator.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

On Thu, 12 Mar 2009 07:18:20 +0000, Kostas Kavoussanakis wrote:

On Tue, 10 Mar 2009, Ed Sirett wrote:

On Tue, 10 Mar 2009 08:08:15 +0000, Kostas Kavoussanakis wrote:

Thanks Ed and Phil,

On Sun, 08 Mar 2009 15:56:08 +0000, Kostas Kavoussanakis wrote:

2. I see Ed says that the calculator tends to undersize. So, should
I aim to set the thermostat to around 2 or 3 (which, if linear,
would be about 12-13 kW, about 30% above the calculation)? Is the
boiler efficient at such a low setting?

The thermostat does not affect the power settings. If the boiler is
switching off an on from time to time during normal operation then
you can be sure that it is big enough. The fact that you have it at a
moderate setting means that you have enough radiator capacity.

I am trying to tune the boiler thermostat for efficiency and learn a
few things in the process if I can. I took it down to 3 (a previous
thread had suggested that it should be all the way up, so as to heat
my cold lounge, but I could hear it short-cycling).

At the moment (~1.5 hours after it started this morning and still
trying to get the Honeywell CM907 to 21 deg) the boiler works for ~2
mins before its stat switches it off for ~3.5 mins; the pump is going
non-stop. Is that still classed as short-cycling?

Also, what is the effect of lowering the water temp? I presume that
the boiler will work for longer periods; does this automatically
suggest higher gas consumption?

I would say from what you have posted that the radiators have to be
hotter in your house to heat the cold lounge. (if that makes the rest
of the house too hot then those radiators need to have TRVs and/or have
them set lower).

Try a higher setting if the lounge is still cold add another radiator.

All (but the one in the hall, where the room stat is) have a TRV. The
idea about a third stat is noted. A previous idea about properly
balancing the whole system may need to take precedence. However, with
the water temp lower the cold lounge "feels" warmer in the evenings
(when it matters on weekdays), maybe because the CH pump works more.
Weekends (when the stat tries to keep 21 deg from 07:30 to 22:30) has
always been another story.

Comfort aside, is there an answer to my initial question about boiler
efficiency? And is "2 mins on 3.5 off" short-cycling, assuming that the
pump works while this is observed?

Technically it is short cycling. How much of a problem depends on your
boiler. A Netaheat (?) would not be too bad with these sort of times.

You will only get rid of short cycling with proper balancing and controls
and a modern boiler.

For the lounge to feel warmer with a cooler boiler setting must mean that
the boiler runs for longer. For you the lounge looks like it's the
hardest room to heat so
either move the thermostat in there and add a TRV to the Hall to stop the
hall over heating.
or add more radiator(s) to the lounge so that room heats up better
relative to the hall.




--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html

On Thu, 12 Mar 2009, Ed Sirett wrote:

On Thu, 12 Mar 2009 07:18:20 +0000, Kostas Kavoussanakis wrote:

Technically it is short cycling. How much of a problem depends on your
boiler. A Netaheat (?) would not be too bad with these sort of times.

Thanks.

You will only get rid of short cycling with proper balancing and controls
and a modern boiler.

The (cost) of the latter just made me appreciate short-cycling :-)

For the lounge to feel warmer with a cooler boiler setting must mean that
the boiler runs for longer. For you the lounge looks like it's the
hardest room to heat so
either move the thermostat in there and add a TRV to the Hall to stop the
hall over heating.
or add more radiator(s) to the lounge so that room heats up better
relative to the hall.

Thanks, all noted!

Kostas