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Radiator sizing for new build house
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Caecilius
Jun 5, 2012, 11:28:25 AM6/5/12
to
I'm building a small two-bedroomed end-terrace house, approx 7 x 5M in
size. Latest building regs, including Part L, so insulation is pretty
good.
I'm going to use a Worcester 25 Si, which is more than sufficient for
this house.I want to use the smallest radiators I can, but obviously
big enough to do the job.
I've used a couple of different calculators, and I'm getting very
different results. The "advanced" calculator on
http://www.radiatorsizingcalculator.co.uk/ is giving me a power
requirement of more than twice what the Barlo heatloss calculator
does.
I'm tending to believe the Barlo heatloss calculator, because although
it's very old, the laws of physics don't change. And the Barlo
calculator allows me to enter the U-Values, whereas I don't know what
assumptions the radiatorsizingcalculator site uses.
For example, with one 2.48m x 2.37m room, the Barlo calculator says I
need 308 watts, which seems incredibly low. The
radiatorsizingcalculator site reckons I need 686 w.
My U-values are:
External wall: 0.16 (2 x 100mm thermalite + 100mm filled cavity)
Windows: 1.5 (Energy Class B uPVC double glazing)
Floor: 0.16 (solid floor with 100mm kooltherm K3)
1st floor ceiling: 0.13
I'm assuming:
Room temp 21 degrees
Outside air temp -1 degrees
Ground temp 10 degrees (guess)
1.5 air changes per hour (guess)
Can anyone see anything obviously wrong with my assumptions,
especially the number of air changes and the ground temp?
It looks like the total heating requirement will be under 3KW, which
seems crazy low for 70 square metres of living space.
size. Latest building regs, including Part L, so insulation is pretty
good.
I'm going to use a Worcester 25 Si, which is more than sufficient for
this house.I want to use the smallest radiators I can, but obviously
big enough to do the job.
I've used a couple of different calculators, and I'm getting very
different results. The "advanced" calculator on
http://www.radiatorsizingcalculator.co.uk/ is giving me a power
requirement of more than twice what the Barlo heatloss calculator
does.
I'm tending to believe the Barlo heatloss calculator, because although
it's very old, the laws of physics don't change. And the Barlo
calculator allows me to enter the U-Values, whereas I don't know what
assumptions the radiatorsizingcalculator site uses.
For example, with one 2.48m x 2.37m room, the Barlo calculator says I
need 308 watts, which seems incredibly low. The
radiatorsizingcalculator site reckons I need 686 w.
My U-values are:
External wall: 0.16 (2 x 100mm thermalite + 100mm filled cavity)
Windows: 1.5 (Energy Class B uPVC double glazing)
Floor: 0.16 (solid floor with 100mm kooltherm K3)
1st floor ceiling: 0.13
I'm assuming:
Room temp 21 degrees
Outside air temp -1 degrees
Ground temp 10 degrees (guess)
1.5 air changes per hour (guess)
Can anyone see anything obviously wrong with my assumptions,
especially the number of air changes and the ground temp?
It looks like the total heating requirement will be under 3KW, which
seems crazy low for 70 square metres of living space.
The Natural Philosopher
Jun 5, 2012, 1:59:38 PM6/5/12
to
larger space (about 200 sq meters)
HOWEVER what you haven't said is what the house is made of: the real
need is not for steady state power but peak power to get a cold house up
to temperature. A lightweight plaster board interior over stud and
rockwool will heat up a lot faster than cavity filled blockwork and
solid concrete floors.
Finally radiators designed fior a 60C flow temperature may be rather
pathetic if you decide one day to put in a heat pump and 40C flow.
In short not many people curse too big radiators - you can turn them
down. But many curse too small radiators..that cant be turned up beyond
fully open.
--
To people who know nothing, anything is possible.
To people who know too much, it is a sad fact
that they know how little is really possible -
and how hard it is to achieve it.
Phil L
Jun 5, 2012, 2:38:44 PM6/5/12
to
My living room is roughly 8m by 3.5m, giving a floor area of 28m2, but it's
2.4m high so my living room is just over 67 cubes.
The room you described in the example above was '2.48m x 2.37m', this gives
a floor area of 5.87m, how do you arrive at 70 square metres?....assuming
the ceiling isn't 11.9m high
Caecilius
Jun 5, 2012, 2:56:04 PM6/5/12
to
On Tue, 05 Jun 2012 18:59:38 +0100, The Natural Philosopher
<t...@invalid.invalid> wrote:
>> It looks like the total heating requirement will be under 3KW, which
>> seems crazy low for 70 square metres of living space.
>
>Not at all. My heating requirements are about 10KW for a much much
>larger space (about 200 sq meters)
I'd guess larger houses are more efficient than smaller houses,
<t...@invalid.invalid> wrote:
>> It looks like the total heating requirement will be under 3KW, which
>> seems crazy low for 70 square metres of living space.
>
>Not at all. My heating requirements are about 10KW for a much much
>larger space (about 200 sq meters)
because the surface area is a square law whereas volume is cube. When
I was getting the energy calculations done, the BCO told me that it
was more difficult to meet the rules for smaller houses like mine.
>HOWEVER what you haven't said is what the house is made of: the real
>need is not for steady state power but peak power to get a cold house up
>to temperature. A lightweight plaster board interior over stud and
>rockwool will heat up a lot faster than cavity filled blockwork and
>solid concrete floors.
This has got a low U-value, but a high thermal mass.
Walls are thermalite block: 100mm thermalite "turbo" block with 100mm
filled cavity. Again, good U-value but maybe fairly high thermal
mass.
The calculator includes a 15% fudge factor to allow for getting the
room up to temperature, but perhaps that's not enough in my case.
>Finally radiators designed fior a 60C flow temperature may be rather
>pathetic if you decide one day to put in a heat pump and 40C flow.
>
>In short not many people curse too big radiators - you can turn them
>down. But many curse too small radiators..that cant be turned up beyond
>fully open.
undersizing.
js.b1
Jun 5, 2012, 3:28:26 PM6/5/12
to
Can you get ACH that low?
I presume you are using heat recovery fan system, if so take care re
outlets & prevailing wind location. The central units are better re
higher static pressure, the stick-in-a-wall type are poor if facing
the prevailing wind.
Have you costed out wet underfloor heating?
2012 insulation is almost enough to need no heat if South facing, but
I am used to living in a barn without even a duvet :-)
I presume you are using heat recovery fan system, if so take care re
outlets & prevailing wind location. The central units are better re
higher static pressure, the stick-in-a-wall type are poor if facing
the prevailing wind.
Have you costed out wet underfloor heating?
2012 insulation is almost enough to need no heat if South facing, but
I am used to living in a barn without even a duvet :-)
Caecilius
Jun 5, 2012, 4:53:57 PM6/5/12
to
On Tue, 5 Jun 2012 19:38:44 +0100, "Phil L" <neverc...@hotmail.com>
wrote:
house dimensions of 5 x 7 metres and two floors. The room details
were an example for just one room in the house. I understood what I
meant when I wrote it, but on re-reading I can see that I was far from
clear.
The ceiling height is 2.4 metres, and I've put that value into the
calculator as well.
And that's a pretty big living room - almost as big as the floor area
of the house I'm building!
wrote:
>It's cubic metres you should be working in, not square metres.
>My living room is roughly 8m by 3.5m, giving a floor area of 28m2, but it's
>2.4m high so my living room is just over 67 cubes.
>The room you described in the example above was '2.48m x 2.37m', this gives
>a floor area of 5.87m, how do you arrive at 70 square metres?....assuming
>the ceiling isn't 11.9m high
The 70 square metres is a total house floor area, which comes from the
>My living room is roughly 8m by 3.5m, giving a floor area of 28m2, but it's
>2.4m high so my living room is just over 67 cubes.
>The room you described in the example above was '2.48m x 2.37m', this gives
>a floor area of 5.87m, how do you arrive at 70 square metres?....assuming
>the ceiling isn't 11.9m high
house dimensions of 5 x 7 metres and two floors. The room details
were an example for just one room in the house. I understood what I
meant when I wrote it, but on re-reading I can see that I was far from
clear.
The ceiling height is 2.4 metres, and I've put that value into the
calculator as well.
And that's a pretty big living room - almost as big as the floor area
of the house I'm building!
Andrew Gabriel
Jun 5, 2012, 6:04:40 PM6/5/12
to
In article <gjkss7tvv6qdegkdn...@4ax.com>,
Yes, I oversized the radiators when designing my system.
I can steady-state heat the house at around 0C outside running
the system at 45/35, which means the boiler is running very
efficiently. (I didn't actually intend it to be quite that
good, but I'm certainly not complaining.)
I also have the option to go up to max running temp to heat
the house up very quickly (which generates about 2.5 times
the heat output).
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
I can steady-state heat the house at around 0C outside running
the system at 45/35, which means the boiler is running very
efficiently. (I didn't actually intend it to be quite that
good, but I'm certainly not complaining.)
I also have the option to go up to max running temp to heat
the house up very quickly (which generates about 2.5 times
the heat output).
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
Tony Bryer
Jun 5, 2012, 6:48:34 PM6/5/12
to
On Tue, 05 Jun 2012 16:28:25 +0100 Caecilius wrote :
> I'm tending to believe the Barlo heatloss calculator, because although
> it's very old, the laws of physics don't change. And the Barlo
> calculator allows me to enter the U-Values, whereas I don't know what
> assumptions the radiatorsizingcalculator site uses.
>
> For example, with one 2.48m x 2.37m room, the Barlo calculator says I
> need 308 watts, which seems incredibly low. The
> radiatorsizingcalculator site reckons I need 686 w.
If you're building to recent Part L standards, ventilation losses may be
> I'm tending to believe the Barlo heatloss calculator, because although
> it's very old, the laws of physics don't change. And the Barlo
> calculator allows me to enter the U-Values, whereas I don't know what
> assumptions the radiatorsizingcalculator site uses.
>
> For example, with one 2.48m x 2.37m room, the Barlo calculator says I
> need 308 watts, which seems incredibly low. The
> radiatorsizingcalculator site reckons I need 686 w.
a significant proportion of the total and are hard to quantify. Even
when you have all the windows closed air will permeate through the
structure. When pressure testing of new dwellings was introduced c.2005
the results obtained showed a range of something like 8:1 between the
leakiest and tightest structures.
--
Tony Bryer, Greentram: 'Software to build on',
Melbourne, Australia www.greentram.com
The Natural Philosopher
Jun 5, 2012, 7:29:35 PM6/5/12
to
"When Sir Henry broke a fast, you cursed double glazing"
Ventilation is ..useful.
harry
Jun 6, 2012, 1:21:40 AM6/6/12
to
On Jun 5, 4:28 pm, Caecilius <nos...@spamless.invalid> wrote:
> I'm building a small two-bedroomed end-terrace house, approx 7 x 5M in
> size. Latest building regs, including Part L, so insulation is pretty
> good.
>
> I'm going to use a Worcester 25 Si, which is more than sufficient for
> this house.I want to use the smallest radiators I can, but obviously
> big enough to do the job.
>
> I've used a couple of different calculators, and I'm getting very
> different results. The "advanced" calculator onhttp://www.radiatorsizingcalculator.co.uk/is giving me a power
> I'm building a small two-bedroomed end-terrace house, approx 7 x 5M in
> size. Latest building regs, including Part L, so insulation is pretty
> good.
>
> I'm going to use a Worcester 25 Si, which is more than sufficient for
> this house.I want to use the smallest radiators I can, but obviously
> big enough to do the job.
>
> I've used a couple of different calculators, and I'm getting very
harry
Jun 6, 2012, 1:31:36 AM6/6/12
to
On Jun 5, 4:28 pm, Caecilius <nos...@spamless.invalid> wrote:
> I'm building a small two-bedroomed end-terrace house, approx 7 x 5M in
> size. Latest building regs, including Part L, so insulation is pretty
> good.
>
> I'm going to use a Worcester 25 Si, which is more than sufficient for
> this house.I want to use the smallest radiators I can, but obviously
> big enough to do the job.
>
> I've used a couple of different calculators, and I'm getting very
> different results. The "advanced" calculator onhttp://www.radiatorsizingcalculator.co.uk/is giving me a power
> size. Latest building regs, including Part L, so insulation is pretty
> good.
>
> I'm going to use a Worcester 25 Si, which is more than sufficient for
> this house.I want to use the smallest radiators I can, but obviously
> big enough to do the job.
>
> I've used a couple of different calculators, and I'm getting very
> requirement of more than twice what the Barlo heatloss calculator
> does.
>
> I'm tending to believe the Barlo heatloss calculator, because although
> it's very old, the laws of physics don't change. And the Barlo
> calculator allows me to enter the U-Values, whereas I don't know what
> assumptions the radiatorsizingcalculator site uses.
>
> For example, with one 2.48m x 2.37m room, the Barlo calculator says I
> need 308 watts, which seems incredibly low. The
> radiatorsizingcalculator site reckons I need 686 w.
>
> My U-values are:
>
> External wall: 0.16 (2 x 100mm thermalite + 100mm filled cavity)
> Windows: 1.5 (Energy Class B uPVC double glazing)
> Floor: 0.16 (solid floor with 100mm kooltherm K3)
> 1st floor ceiling: 0.13
>
> I'm assuming:
>
> Room temp 21 degrees
> Outside air temp -1 degrees
> Ground temp 10 degrees (guess)
> 1.5 air changes per hour (guess)
>
> Can anyone see anything obviously wrong with my assumptions,
> especially the number of air changes and the ground temp?
>
> It looks like the total heating requirement will be under 3KW, which
> seems crazy low for 70 square metres of living space.
Well I would throw your "Barlow calculator" away, it is complete
> does.
>
> I'm tending to believe the Barlo heatloss calculator, because although
> it's very old, the laws of physics don't change. And the Barlo
> calculator allows me to enter the U-Values, whereas I don't know what
> assumptions the radiatorsizingcalculator site uses.
>
> For example, with one 2.48m x 2.37m room, the Barlo calculator says I
> need 308 watts, which seems incredibly low. The
> radiatorsizingcalculator site reckons I need 686 w.
>
> My U-values are:
>
> External wall: 0.16 (2 x 100mm thermalite + 100mm filled cavity)
> Windows: 1.5 (Energy Class B uPVC double glazing)
> Floor: 0.16 (solid floor with 100mm kooltherm K3)
> 1st floor ceiling: 0.13
>
> I'm assuming:
>
> Room temp 21 degrees
> Outside air temp -1 degrees
> Ground temp 10 degrees (guess)
> 1.5 air changes per hour (guess)
>
> Can anyone see anything obviously wrong with my assumptions,
> especially the number of air changes and the ground temp?
>
> It looks like the total heating requirement will be under 3KW, which
> seems crazy low for 70 square metres of living space.
crap.
The heat loss is workedout by measuring up the area of exterior wall,
windows, roof and floor.
Each area is mutliplied by relevant U value and temp.difference.
Then they are totalled up and a "funk factor " added. For air changes,
draughts, hot water etc.
You want to get your head around the idea of the boiler perhaps being
a little small and the radiators oversize to keep the water
temperatures down, so boosting efficiency. Oversized boilers are a
very bad thing.
The output of radiators depends on water flow and temp, the way they
are connected, ambient temperature and how "exposed" they are in their
location,
The manufactureres data is just a guideline.
Steve Firth
Jun 6, 2012, 2:01:34 AM6/6/12
to
harry
Jun 6, 2012, 2:50:06 PM6/6/12
to
On Jun 6, 7:01 am, Steve Firth <%ste...@malloc.co.uk> wrote:
> harry <haroldhr...@aol.com> wrote:
>
> [NOTHING]
>
> Most intelligent thing you have said to-date harry.
How would you know?
>
> [NOTHING]
>
> Most intelligent thing you have said to-date harry.
Steve Firth
Jun 6, 2012, 4:41:41 PM6/6/12
to
Caecilius
Jun 7, 2012, 11:54:20 AM6/7/12
to
On Tue, 5 Jun 2012 22:31:36 -0700 (PDT), harry <harol...@aol.com>
wrote:
check the figures for one room manually to make sure. It doesn't look
like a difficult calculation, given that I know the dimentions,
temperatures and U-values already.
>Then they are totalled up and a "funk factor " added. For air changes,
>draughts, hot water etc.
Yes, that's right.
>You want to get your head around the idea of the boiler perhaps being
>a little small and the radiators oversize to keep the water
>temperatures down, so boosting efficiency. Oversized boilers are a
>very bad thing.
The boiler I've chosen is about the smallest I can get from the
Worcester Bosch range. It's quoted CH output is 7.2 to 24KW. I guess
that means it can modulate down to 7.2KW. With a load below that, as
it looks mine will be at steady-state, I guess it'll just cycle on and
off.
>The output of radiators depends on water flow and temp, the way they
>are connected, ambient temperature and how "exposed" they are in their
>location,
>The manufactureres data is just a guideline.
I think you can turn down the temperature on modern condensing boilers
can't you? So if my rads are oversized, I could run the CH at 50
degrees or something.
wrote:
>Well I would throw your "Barlow calculator" away, it is complete
>crap.
>
>The heat loss is workedout by measuring up the area of exterior wall,
>windows, roof and floor.
>
>Each area is mutliplied by relevant U value and temp.difference.
I suspect this is what th Barlo calculator is doing. But I think It'll
>crap.
>
>The heat loss is workedout by measuring up the area of exterior wall,
>windows, roof and floor.
>
>Each area is mutliplied by relevant U value and temp.difference.
check the figures for one room manually to make sure. It doesn't look
like a difficult calculation, given that I know the dimentions,
temperatures and U-values already.
>Then they are totalled up and a "funk factor " added. For air changes,
>draughts, hot water etc.
>You want to get your head around the idea of the boiler perhaps being
>a little small and the radiators oversize to keep the water
>temperatures down, so boosting efficiency. Oversized boilers are a
>very bad thing.
Worcester Bosch range. It's quoted CH output is 7.2 to 24KW. I guess
that means it can modulate down to 7.2KW. With a load below that, as
it looks mine will be at steady-state, I guess it'll just cycle on and
off.
>The output of radiators depends on water flow and temp, the way they
>are connected, ambient temperature and how "exposed" they are in their
>location,
>The manufactureres data is just a guideline.
can't you? So if my rads are oversized, I could run the CH at 50
degrees or something.
gremlin_95
Jun 7, 2012, 12:34:30 PM6/7/12
to
On 07/06/2012 16:54, Caecilius wrote:
> The boiler I've chosen is about the smallest I can get from the
> Worcester Bosch range. It's quoted CH output is 7.2 to 24KW. I guess
> that means it can modulate down to 7.2KW. With a load below that, as
> it looks mine will be at steady-state, I guess it'll just cycle on and
> off.
>
>
Is this a combi boiler?
> The boiler I've chosen is about the smallest I can get from the
> Worcester Bosch range. It's quoted CH output is 7.2 to 24KW. I guess
> that means it can modulate down to 7.2KW. With a load below that, as
> it looks mine will be at steady-state, I guess it'll just cycle on and
> off.
>
>
Have a look at the Vaillant range, their new range modulate quite low.
The 831 combination boiler has a range of 5.2 - 24.0 kw, same range for
the 24 kw system boiler. The 18kw system boiler has a range of 3.8kw -
18.0kw whilst the 15kw model goes down to 3kw. A wider modulation range
will stop the boiler cycling so much when the demand isn't very high.
--
David
Caecilius
Jun 7, 2012, 3:26:55 PM6/7/12
to
On Thu, 07 Jun 2012 17:34:30 +0100, gremlin_95 <daw**dseed@g**ail.com>
wrote:
>Have a look at the Vaillant range, their new range modulate quite low.
>The 831 combination boiler has a range of 5.2 - 24.0 kw
Thanks. I'll take a look at the valliant boilers.
wrote:
>Is this a combi boiler?
Yes, it's a combi.
>Have a look at the Vaillant range, their new range modulate quite low.
>The 831 combination boiler has a range of 5.2 - 24.0 kw
Andrew Gabriel
Jun 7, 2012, 3:51:55 PM6/7/12
to
In article <jqql6n$6mf$1...@dont-email.me>,
of the software which operates the boiler.
My 20+ year old Potterton Profile cycles on and off with pretty much
no energy wastage (and it's designed to - it can't modulate).
Conversely, my 10+ year old Keston condensing boiler is really dumb
about cycling on and off, and probably wastes significant energy in
doing so when demand is less than 7kW lowest modulation level.
(It spends 2 minutes cooling the heat exchanger, regardless if it
needs it or not, and in my case it mostly doesn't, so it's just
wasting the heat in the circulating water, blowing it out the flue.)
Fortunately, it has a large hysteresis, so it doesn't cycle too
often.
gremlin_95 <daw**dseed@g**ail.com> writes:
> Is this a combi boiler?
>
> Have a look at the Vaillant range, their new range modulate quite low.
> The 831 combination boiler has a range of 5.2 - 24.0 kw, same range for
> the 24 kw system boiler. The 18kw system boiler has a range of 3.8kw -
> 18.0kw whilst the 15kw model goes down to 3kw. A wider modulation range
> will stop the boiler cycling so much when the demand isn't very high.
Cycling isn't necessarily an issue - it depends heavily on the design
> Is this a combi boiler?
>
> Have a look at the Vaillant range, their new range modulate quite low.
> The 831 combination boiler has a range of 5.2 - 24.0 kw, same range for
> the 24 kw system boiler. The 18kw system boiler has a range of 3.8kw -
> 18.0kw whilst the 15kw model goes down to 3kw. A wider modulation range
> will stop the boiler cycling so much when the demand isn't very high.
of the software which operates the boiler.
My 20+ year old Potterton Profile cycles on and off with pretty much
no energy wastage (and it's designed to - it can't modulate).
Conversely, my 10+ year old Keston condensing boiler is really dumb
about cycling on and off, and probably wastes significant energy in
doing so when demand is less than 7kW lowest modulation level.
(It spends 2 minutes cooling the heat exchanger, regardless if it
needs it or not, and in my case it mostly doesn't, so it's just
wasting the heat in the circulating water, blowing it out the flue.)
Fortunately, it has a large hysteresis, so it doesn't cycle too
often.
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