I am sure this has come up 100 times, but are any of the web-based
radiator size calculators any good. I tried http://www.radcalcs.com/

Do radiators fitted 15-20 years ago give out a lot less heat for their
size?

Thanks for any info.

Mr F.

On Mon, 25 Jul 2005 20:24:03 +0100, Mr Fizzion
wrote:

I am sure this has come up 100 times, but are any of the web-based
radiator size calculators any good. I tried http://www.radcalcs.com/

Do radiators fitted 15-20 years ago give out a lot less heat for their
size?

Thanks for any info.

Mr F.


Nope. Send me a mail and I'll send you a copy of the Myson one. That
is no longer on their web site but works OK.

You can also use a spreadsheet if you have the U vales of the
materials.

Regarding radiators, the main factors that affect output, for a given
flow and return temperature are whether fins are fitted.



--

..andy

To email, substitute .nospam with .gl

Andy Hall wrote:
On Mon, 25 Jul 2005 20:24:03 +0100, Mr Fizzion
wrote:


I am sure this has come up 100 times, but are any of the web-based
radiator size calculators any good. I tried http://www.radcalcs.com/

Do radiators fitted 15-20 years ago give out a lot less heat for their
size?



Nope. Send me a mail and I'll send you a copy of the Myson one. That
is no longer on their web site but works OK.

Not sure which question you're answering there, Andy, but are you saying
that the radcalcs one is no good? I have it in my 'Favourites' and as
it happens, was going to use it myself this week. What's the problem
with it?!

Would appreciate a copy of your Myson prog if you wouldn't mind - my
hotmail address is valid.

Thanks
David

Mr Fizzion wrote:
I am sure this has come up 100 times, but are any of the web-based
radiator size calculators any good. I tried http://www.radcalcs.com/

Do radiators fitted 15-20 years ago give out a lot less heat for their
size?

If still in as-new-condition & same material (normally steel) then o/p
is similar, but watch for internal corrosion, silting up,
blocked/reduced diameter inlets & outlets on old installations.

Basically a standard pattern panel radiator can have (a) no fins (b)
fins one side (c) fins on both sides - each one adds a bit more to
output, provided your CH can pump the requisite extra quantity of heat
from the boiler. (It can't do that if other radiators leave no surplus
heat). Then you can double (& treble) up any of the 3 panel+fin styles
to make a thicker radiator etc etc. But as you add more panels & fins
air circulates away less easily & so output per sq m doesn't rise quite
as fast the extra fins might sugggest. eg doubling up doesn't quite
double radiator maximum output (somewhere in the range 1.9 to 1.95
IIRC).

There is (or was) a Which book on plumbing/CH which had a handy rule of
thumb for sizing - measure the cubic capacity of the room in cubic feet
& multiply by 5 for downstairs & 4 for a cooler upstairs. The result
is the radiator size in BThU.

Works very well in my experience. & provides a decent margin for boiler
capacity. Remember, unless yours are special or unusual circumstances,
you are only sizing to ensure your ch keeps you warm on maybe only 7 of
the coldest days in the year + ensuring you'll get a decent supply of
hot water on those days. Rest of the time your boiler will always be
working under capacity, which it achieves by switching off for
increasing time spans during the day as summer approaches.

Up the 5 & 4 to 6 & 5 if a cold old house, reduce if it is modern part
L house.

All in all, IMHE it pays to be generous with boiler & radiator sizing,
it doesn't cost much extra to modestly oversize, & all that happens is
that your boiler stays off for longer - it doesn't mean you'll burn
more fuel. So use calc progs just to check you aren't undersizing (&
to make sure your ch pipes are the right diameter).

HTH

On Mon, 25 Jul 2005 22:08:35 GMT, Lobster
wrote:

Andy Hall wrote:
On Mon, 25 Jul 2005 20:24:03 +0100, Mr Fizzion
wrote:


I am sure this has come up 100 times, but are any of the web-based
radiator size calculators any good. I tried http://www.radcalcs.com/

Do radiators fitted 15-20 years ago give out a lot less heat for their
size?



Nope. Send me a mail and I'll send you a copy of the Myson one. That
is no longer on their web site but works OK.

Not sure which question you're answering there, Andy, but are you saying
that the radcalcs one is no good? I have it in my 'Favourites' and as
it happens, was going to use it myself this week. What's the problem
with it?!

Last time I used it a few months ago, it was out by a factor of 3 (too
high on radiator sizes) compared with the Myson one and hand
calculation. It seemed to be a combination of some U values being
incorrect and wrong arithmetic. I didn't investigate in detail to be
honest.



Would appreciate a copy of your Myson prog if you wouldn't mind - my
hotmail address is valid.

On its way to you.



--

..andy

To email, substitute .nospam with .gl

On 25 Jul 2005 15:20:29 -0700, wrote:



Mr Fizzion wrote:
I am sure this has come up 100 times, but are any of the web-based
radiator size calculators any good. I tried http://www.radcalcs.com/

Do radiators fitted 15-20 years ago give out a lot less heat for their
size?

If still in as-new-condition & same material (normally steel) then o/p
is similar, but watch for internal corrosion, silting up,
blocked/reduced diameter inlets & outlets on old installations.

Basically a standard pattern panel radiator can have (a) no fins (b)
fins one side (c) fins on both sides - each one adds a bit more to
output, provided your CH can pump the requisite extra quantity of heat
from the boiler. (It can't do that if other radiators leave no surplus
heat). Then you can double (& treble) up any of the 3 panel+fin styles
to make a thicker radiator etc etc. But as you add more panels & fins
air circulates away less easily & so output per sq m doesn't rise quite
as fast the extra fins might sugggest. eg doubling up doesn't quite
double radiator maximum output (somewhere in the range 1.9 to 1.95
IIRC).

There is (or was) a Which book on plumbing/CH which had a handy rule of
thumb for sizing - measure the cubic capacity of the room in cubic feet
& multiply by 5 for downstairs & 4 for a cooler upstairs. The result
is the radiator size in BThU.

This is very rough and ready and hopefully is generous. There is an
enormous difference in heat loss for a house with solid brick walls
and single glazing vs. one with insulated cavity walls and double
glazing.

It can be as much as 5:1 difference, so these approximations can
really lead to tears in terms of undersizing or oversizing.

Also, it is better to stick to metric units throughout. Feet and
BThUs are pretty much out of use on data sheets and it's very unwise
to mix and convert because it can easily lead to errors.




Works very well in my experience. & provides a decent margin for boiler
capacity. Remember, unless yours are special or unusual circumstances,
you are only sizing to ensure your ch keeps you warm on maybe only 7 of
the coldest days in the year + ensuring you'll get a decent supply of
hot water on those days. Rest of the time your boiler will always be
working under capacity, which it achieves by switching off for
increasing time spans during the day as summer approaches.

Up the 5 & 4 to 6 & 5 if a cold old house, reduce if it is modern part
L house.

The differences cn be far more than these factors suggest.



All in all, IMHE it pays to be generous with boiler & radiator sizing,
it doesn't cost much extra to modestly oversize, & all that happens is
that your boiler stays off for longer - it doesn't mean you'll burn
more fuel.

That's true enough. It's reasonable to oversize somewhat with a
condensing boiler because the system can then run cooler and more
efficiently for most of the time. However radiators with larger
output start to cost quite a bit more and may take up more wall space.


So use calc progs just to check you aren't undersizing (&
to make sure your ch pipes are the right diameter).


It's better to use proper calculation in the first place, check the U
values and use that for the sizing.



--

..andy

To email, substitute .nospam with .gl

On 25 Jul 2005 15:20:29 -0700, wrote:


Rest of the time your boiler will always be
working under capacity, which it achieves by switching off for
increasing time spans during the day as summer approaches.

If the boiler is modulating will this be different? Will it simply
adjust the burn rate instead of switching on and off?

Mr F

"Andy Hall" wrote in message
...
On 25 Jul 2005 15:20:29 -0700, wrote:



Mr Fizzion wrote:
I am sure this has come up 100 times, but are any of the web-based
radiator size calculators any good. I tried http://www.radcalcs.com/

Do radiators fitted 15-20 years ago give out a lot less heat for their
size?

If still in as-new-condition & same material (normally steel) then o/p
is similar, but watch for internal corrosion, silting up,
blocked/reduced diameter inlets & outlets on old installations.

Basically a standard pattern panel radiator can have (a) no fins (b)
fins one side (c) fins on both sides - each one adds a bit more to
output, provided your CH can pump the requisite extra quantity of heat
from the boiler. (It can't do that if other radiators leave no surplus
heat). Then you can double (& treble) up any of the 3 panel+fin styles
to make a thicker radiator etc etc. But as you add more panels & fins
air circulates away less easily & so output per sq m doesn't rise quite
as fast the extra fins might sugggest. eg doubling up doesn't quite
double radiator maximum output (somewhere in the range 1.9 to 1.95
IIRC).

There is (or was) a Which book on plumbing/CH which had a handy rule of
thumb for sizing - measure the cubic capacity of the room in cubic feet
& multiply by 5 for downstairs & 4 for a cooler upstairs. The result
is the radiator size in BThU.

This is very rough and ready and hopefully is generous. There is an
enormous difference in heat loss for a house with solid brick walls
and single glazing vs. one with insulated cavity walls and double
glazing.

It can be as much as 5:1 difference, so these approximations can
really lead to tears in terms of undersizing or oversizing.

Best he fist cavity wall insulation.

Also, it is better to stick to metric units throughout. Feet and
BThUs are pretty much out of use on data sheets and it's very unwise
to mix and convert because it can easily lead to errors.

Works very well in my experience. & provides a decent margin for boiler
capacity. Remember, unless yours are special or unusual circumstances,
you are only sizing to ensure your ch keeps you warm on maybe only 7 of
the coldest days in the year + ensuring you'll get a decent supply of
hot water on those days. Rest of the time your boiler will always be
working under capacity, which it achieves by switching off for
increasing time spans during the day as summer approaches.

Up the 5 & 4 to 6 & 5 if a cold old house, reduce if it is modern part
L house.

The differences cn be far more than these factors suggest.



All in all, IMHE it pays to be generous with boiler & radiator sizing,
it doesn't cost much extra to modestly oversize, & all that happens is
that your boiler stays off for longer - it doesn't mean you'll burn
more fuel.

That's true enough. It's reasonable to oversize somewhat with a
condensing boiler because the system can then run cooler and more
efficiently for most of the time. However radiators with larger
output start to cost quite a bit more and may take up more wall space.


So use calc progs just to check you aren't undersizing (&
to make sure your ch pipes are the right diameter).


It's better to use proper calculation in the first place, check the U
values and use that for the sizing.



--

.andy

To email, substitute .nospam with .gl

On Mon, 25 Jul 2005 23:55:34 +0100, Mr Fizzion
wrote:

On 25 Jul 2005 15:20:29 -0700, wrote:


Rest of the time your boiler will always be
working under capacity, which it achieves by switching off for
increasing time spans during the day as summer approaches.

If the boiler is modulating will this be different? Will it simply
adjust the burn rate instead of switching on and off?

Mr F



Yes it will, down to the lower limit of the boiler output. For a
condensing boiler, it's worth doing.

You can make a further improvement with a condensing boiler by
designing the system to run the radiators at 70 degrees flow and 50
return rather than the 82 and 70 used for a conventional boiler.

However....... Look up the tables on the radiator manufacturer data
sheet to determine radiator sizing.

THe default output relates to a laboratory measured radiator test
method. To obtain practical outputs, a correction factor is applied.
This is around 0.9 for 82/70 operation and around 0.6 for 70/50. It
is based on mean water to air temperature which is basically the
midpoint temperature of the radiator (76 or 60 degrees) less the room
temperature. A table of correction factors for different room
temperatures is usually on the data sheet.

To pick a simple example. Let's say you needed 600W of heat to
overcome the room heat loss and you are going to use 70/50 degrees.
Using the correction factor of 0.6, you would need a radiator of
nominal 1000W output.



--

..andy

To email, substitute .nospam with .gl

On Mon, 25 Jul 2005 23:56:13 +0100, "Doctor Drivel"
wrote:


"Andy Hall" wrote in message
.. .
On 25 Jul 2005 15:20:29 -0700, wrote:


Best he fist cavity wall insulation.

I didn't know that you were into that.....

I would have thought that it would have felt prickly.



--

..andy

To email, substitute .nospam with .gl

"Doctor Drivel" wrote:

Best he fist cavity wall insulation.

Pervert


Oh you can go home now drivel but you'll have to sell a few more
copper tanks tomorrow. Head office cancelled the combi order you
tried to sneak through as no one wants them anymore.




--

Mr Fizzion wrote:
On 25 Jul 2005 15:20:29 -0700, wrote:


Rest of the time your boiler will always be
working under capacity, which it achieves by switching off for
increasing time spans during the day as summer approaches.

If the boiler is modulating will this be different? Will it simply
adjust the burn rate instead of switching on and off?

in principal it makes no difference, but:

It is *not* like comparing the fuel connsumption of a 2 litre model T
with a 1 litre version.

Basic scenario is [leaving aside many ifs & buts]:

1. Your home in given external weather conditions requires a fixed
amount of heat to maintain whatever temperature you select.

2. Standard/conventional/normal [ie not heat pumps etc] UK oil & gas CH
systems simply release the stored energy (commonly called the fuel's
calorific value) binding the fuel's hydrocarbon molecules together by
combining it with atmospheric oxygen (ie burning) to create chemicals
(mostly CO2 & H2O) which require less energy to bind their molecules.
The unwanted energy is released as heat.

3. Because of the principal of conservation of energy, it doesn't
matter how fast or slowly your fuel burns - a fixed amount of fuel
will produce a fixed amount of heat [assuming your heating system
produces/does no mechanical work]. Assuming all the fuel fed into the
boiler is burnt, then the size & design of the boiler makes no
difference to this fundamental fact.

4. The heat produced warms the house via the radiators [useful heat] &
warms up the flue gasses which in turn warm up your garden [wasted
heat].

5. Boiler design can only alter the balance between useful heat & waste
heat. So keeping the boiler design the same, a larger boiler should
use just the same amount of fuel as a smaller one of the same design -
but if it burns the fuel faster, then the CH system will shut down more
so that only just the amount of heat required by your home (see 1
above) is generated.

OTOH spending more on a larger boiler *could* mean you buy a boiler
with a different design which proportionally pushes out more (or less)
waste heat. But that makes no difference to the fundamental situation
when you are comparing like with like.

6. That's the simple picture. It gets more complicated when you don't
ignore the ifs & buts & consider second order heat losses & other
factors, though they won't normally make a significant difference to
the overall energy picture [even so any savings thrown up are usually
worth having].

7. Car engines are different. Here, in broad terms, you have a heat
engine which is subject to the second law of thermodynamics. The fuel
is burnt in the engine to produce heat. When the driver calls for it
(by pressing the accelerator) the engine converts some of that heat
into work. ie the heat is a reservoir from which work is extracted.
Otherwise the heat is wasted/lost via the radiator coolant & exhaust
gas & by warming air blown over the engine by the fan.

A larger engine maintains a greater heat resource (ie uses more fuel) &
can thus provide more work.

Thus, as the car engine is kept running all the time, an oversized
engine, unlike an oversized CH system, will use more fuel than a
smaller one to undertake the same task (eg a journey).

What happens to that wasted heat the car engine generates while it
provides work? It heats up the planet....but that is where heat pumps
begin.


HTH