I need to size a new boiler, hence I need to size the radiators for each
room.

There are a lot of heat loss calculators out there, but, depending upon
the one I use, I get values of between 733W and 3.3kW for the same room.
Unfortunately, they don't say what assumptions are being made to get
those results.

Has anyone used one that they can recommend as giving results that
actually work in real life?

Colin Bignell

On Wed, 31 Mar 2010 17:50:07 +0100, Nightjar \"cpb\"@ wrote:

I need to size a new boiler, hence I need to size the radiators for each
room.

The standard method for sizing boilers is not to do a detailed heatloss
for each room but to use a differnet calculator. I think ther are links to
some online ones on the wiki but I can email you my spreadsheet version.



--
John Stumbles -- http://yaph.co.uk

Little Johnny's gone away, his like we'll see no more
For what he thought was H20 was H2SO4

On Wed, 31 Mar 2010 19:55:33 +0000, YAPH wrote:

The standard method for sizing boilers is not to do a detailed heatloss
for each room but to use a differnet calculator. I think ther are links
to some online ones on the wiki but I can email you my spreadsheet
version.

.... if you drop me an email (my address is valid but the obfuscation of
yours defeats my poor knackered brain :-/)


--
John Stumbles -- http://yaph.co.uk

I'm more non-competitive than you

YAPH wrote:
On Wed, 31 Mar 2010 19:55:33 +0000, YAPH wrote:

The standard method for sizing boilers is not to do a detailed heatloss
for each room but to use a differnet calculator. I think ther are links
to some online ones on the wiki but I can email you my spreadsheet
version.

... if you drop me an email (my address is valid but the obfuscation of
yours defeats my poor knackered brain :-/)



Thank you. I did look at boiler sizing calculators, but they seem to
assume a fairly consistent form of construction. My house is about 80
years old and has been extended at various times, under various sets of
building regs, so I have insulated and uninsulated cavity walls, to
differing levels of insulation, an insulated loft, an uninsulated flat
roof, an insulated flat roof, single glazed wooden windows, double
glazed uPVC windows, and a heated double glazed conservatory. I think
the only way is to work out the loss room by room and add those to get
the loss of the whole house.

I am coming to the conclusion that I will have to follow John's
suggestion and put it all in a spreadsheet. That would also have the
advantage that I could quickly see the effect and savings, if any, of
different types of additional insulation. The main problem is that I
tend to get carried away writing spreadsheets and end up with huge ones.

Colin Bignell

YAPH wrote:
On Wed, 31 Mar 2010 17:50:07 +0100, Nightjar \"cpb\"@ wrote:

I need to size a new boiler, hence I need to size the radiators for each
room.

The standard method for sizing boilers is not to do a detailed heatloss
for each room but to use a differnet calculator. I think ther are links to
some online ones on the wiki but I can email you my spreadsheet version.



Correct. The boiler has simply to be large enough to manage the house
total heatloss at say -5C ambient, and have a bit spare for reasonably
fast heating.

Radiators are sized to the room, boilers to the whole house..

In message , "Nightjar
\"cpb\"@" writes

I need to size a new boiler, hence I need to size the radiators for
each room.

There are a lot of heat loss calculators out there, but, depending upon
the one I use, I get values of between 733W and 3.3kW for the same
room. Unfortunately, they don't say what assumptions are being made
to get those results.

Has anyone used one that they can recommend as giving results that
actually work in real life?


I've got a copy of the old Myson Heatloss Program, passed onto me by the
late Andy Hall. Old, but still seems to do the job. You can set the
variables (U values, room temps etc.) so you know what's happening.

Drop me an email (reply to is valid) if you'd like a copy.
--
Chris French

chris French wrote:
In message , "Nightjar
\"cpb\"@" writes

I need to size a new boiler, hence I need to size the radiators for
each room.

There are a lot of heat loss calculators out there, but, depending
upon the one I use, I get values of between 733W and 3.3kW for the
same room. Unfortunately, they don't say what assumptions are being
made to get those results.

Has anyone used one that they can recommend as giving results that
actually work in real life?


I've got a copy of the old Myson Heatloss Program, passed onto me by the
late Andy Hall. Old, but still seems to do the job. You can set the
variables (U values, room temps etc.) so you know what's happening.

Drop me an email (reply to is valid) if you'd like a copy.

Thank you. I have a copy I downloaded from their site ages ago. The
problem I have is knowing whether to believe that, or the one provided
by Plumb Center, or the one given by Ultraheat, or the City Plumbing
one, or the one at Heatlosscalculator.co.uk etc. They all give different
results, some wildly different. I suspect I shall have to do as John
suggests and do the calculations myself.

Colin Bignell

On Thu, 01 Apr 2010 02:12:13 +0100
"Nightjar \"cpb\"@" "insertmysurnamehere wrote:
....I suspect I shall have to do as John
suggests and do the calculations myself.

Colin Bignell


I strongly suggest you do, and then maintain the spreadsheet. I am
forever returning to mine, and doing 'what if' type things with it.
E.g., this bedroom seems cold, what if I added 25mm Celotex to the
outside wall when I decorate? 40mm, 60mm, etc..

I also started making it ever more detailed and checking each room for
conformance with the model. By doing this I have discovered that the
source of the coldness in the kitchen, which the model says should be
18, is the meter cupboard (1970's bungalow, wiring runs to the loft via
the cavity, so no cavity fill behind the meter cupboard) - the cold air
is actually coming from the cavity through the CU! Solution cheap and
obvious!

R.

TheOldFellow wrote:
On Thu, 01 Apr 2010 02:12:13 +0100
"Nightjar \"cpb\"@" "insertmysurnamehere wrote:
...I suspect I shall have to do as John
suggests and do the calculations myself.

Colin Bignell


I strongly suggest you do, and then maintain the spreadsheet. I am
forever returning to mine, and doing 'what if' type things with it.
E.g., this bedroom seems cold, what if I added 25mm Celotex to the
outside wall when I decorate? 40mm, 60mm, etc..

I'd not thought of allowing for adding extra insulation inside the wall.
So, that is a check box to remove and another drop list to add. So far,
I have drop lists for four different insulation levels for the suspended
floors, along with different U-values depending upon the perimeter to
area ratios, - I can't do much about the solid ones - six different ways
to improve the main roof insulation, four different options for the
uninsulated flat roof, including two that involve replacing it with a
lean-to pitched roof, three different options for improving the original
windows, four different outside temperatures and several different
options for room temperatures, as I have never found the standard set of
room temperatures comfortable.

I also started making it ever more detailed and checking each room for
conformance with the model. By doing this I have discovered that the
source of the coldness in the kitchen, which the model says should be
18, is the meter cupboard (1970's bungalow, wiring runs to the loft via
the cavity, so no cavity fill behind the meter cupboard) - the cold air
is actually coming from the cavity through the CU! Solution cheap and
obvious!

I've got something similar, except that the hole is above the CU. The
hole is flagged for covering if I get the cavity wall insulated, if only
to stop the stuff pouring out into the cupboard.

Colin Bignell

Thank you. I have a copy I downloaded from their site ages ago. The
problem I have is knowing whether to believe that, or the one provided
by Plumb Center, or the one given by Ultraheat, or the City Plumbing
one, or the one at Heatlosscalculator.co.uk etc. They all give
different results, some wildly different. I suspect I shall have to
do as John suggests and do the calculations myself.

Colin Bignell

I use the Myson program and it delivers results which I believe. I'm not
familiar with the others which you mention, but I know that some on-line
calculators seem to use "rules of thumb" rather than doing the calcs
rigorously - and so might get widely varying results.

The Myson program (and also the one from Barlo, which is very similar) take
account of all the necessary parameters - external and internal
temperatures, areas of walls, windows, ceilings, floors - all with
appropriate U values, air changes, etc.

It has standard U values for all standard types of wall, window, floor,
roof, etc. construction - but you can subsistute your own if you prefer.
[You'd have to do that with a spreadsheet, anyway].

Having worked out the steady-state heat loss for each room under the
specified conditions, it adds on a bit more for transients, and a bit more
still for pipe losses - but you have control over those, and can change or
omit the grossing up factors if you prefer. It's probably in this area where
the different programs give different results - because they make different
assumptions about the amount of grossing up required (and possibly about air
changes - and allowances for DHW heating when sizing the boiler). One good
thing about the Myson program is that you can *see* how it is doing the
calcs, and change the assumptions if you don't like the default ones.
--
Cheers,
Roger
_______
Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

I have just been through the same experience. I used about a half
dozen of them and the results varied by a factor of three.
I found that the most basic programs pretty much ask you for the room
size and that's all, they then just assume worst case ie. no loft
insulation, wall insulation etc and will give you the highest BTU
readings.
The better one's ask more questions. ie. number of ouside walls, floor
type etc.
I think I used radcalc.com which gave the lowest values and then added
50% for good measure. The boiler and rads are now running and it is
plenty warm.

I tried a few of these heatloss calculators and, like you, I got
values all over the place.

Mine's a chapel conversion with a double-height main area, very high
ceilinged downstairs rooms, whilst part of the upstairs room follows
the roofline - i.e all stuff that an online calculator won't follow
well.

In the end, I had a think about "how many 2kW fan heaters to pull this
room up to temperature from cold, on a very cold day" - i.e I pretty
much went for my gut feeling for what sort of heat output I wanted for
each radiator. Then added a bit.

Then had a think about what physical size of rad would fit each
location. Then went round again and worked out what standard size of
rad I could use in as many locations as possible. Then worked out how
to get them in heat-pack deal from an online supplier.

Finally result had virtually nothing to do with the calculated size,
other than its somewhat bigger.

Boiler I ended up buying a long way in advance of all of this - sizing
based on similar "big enough and add a bit".

The insulation levels are now also considerably higher than originally
planned (but depending on the weather, there may be drafts from the
under-building void through the original timber boards downstairs).

The final outcome? Cosy, and very modest bills indeed.

My conclusions - the calcs are more using for giving plumbing students
something to do in their college exams - and estimates based on
personal impressions are as good, when considering a problem without a
comprehensive set of accurate values to base calculations on.