How do you feel about this being put on the wiki? Could be useful
information I think.
PS cant get goggle group to reply to thread :/
The Natural Philosopher wrote:
Ok, found the book
This is U values not K. Watts per sq meter per degree K.
DG windows range from 2.2 to 4.2..depending on gap, filling and
SG windows are in the range 4.7-5.8 depending on frame.
Note a good wood frame SG is almost as good as a crap DG metal
solid doors are about 3.
9" solid brick wall about 3.5
4.5" single brick wall 7.
10mm expanded polystyrene or rock wool or 6mm Celotex 3.5
..yes folks, thats how little will HALVE the heat loss through a 9"
solid brick wall. and if its a single 4.5" brick wall..just 5mm of
polystyrene will halve it, too..
15mm plasterboard has a U value of about 10.
15mm of wood paneling is about a U value of 10 too.
Its very instructive to see how a brick wall without cavity, a window
and a door are all very similar..this is typical Victorian style
construction, and how little 15mm of wood flooring will help with an
underfloor vented cavity, or 15mm of plasterboard ceiling will help
a vented roof cavity..Brr!.
Its also very instructive to see how little insulation is needed to
a substantial difference to this sort of property.
Now building regs are trying to get U values down below 0.3
overall..about TEN TIMES better than a Victorian 'as built' standard.
You can instantly see that uninsulated plasterboard ceilings to a
vented roof are by far and away the worst losers of heat. Which
vindicates the emphasis on loft insulation.
Its also easy to see why Britain, with loads of suspended wooden
has a penchant for fitted carpets with thick underlay..
Its very hard to see why double glazing is so insisted on.
Its very easy to see just how bad solid brick walls are as well..and
remember a cavity wall with exterior air bricks is not far off a 4.5"
single brick wall, in a moderate breeze..you don't need a lot of
insulation to radically improve these sorts of wall..dry lining with
just 1/4" of Celotex will halve the heat loss through a solid brick
wall. Add in 15mm of plasterboard and U value is down to 1.5 from
For a total loss in room dimensions of less than an inch all round
exterior walls. No brainer innit?
Now lets consider a room - say its 12x8 ft. and 8ft high, with two
external walls. So external area is 96+64=186 sq ft..and lets
it has a suspended floor and be generous with carpeting and put that
U value of 3.5 same as the walls.. so another 96 sq ft takes us to
Thats a total area of 25 sq meters. Lets assume an average annual
internal temp of 19C and 14C average annual external..so 5C drop..so
watts required is 5x3.5x25= 437.5 watts. And a peak requirement at
external of 5 times that..2187 watts.
Consider how we might improve all this.
Let's say we have two windows totalling 2.5 sq meters. At a U value
5..so thats just 8% of the total heatloss from the room. A GOOD DG
should more than halve that..netting us a 4% gain, or ariound 17.5
average, and annualized around 155KWh..say at 10p per unit..£15 a
gain.For probably about £1500 outlay. So a 1% ROI.
Now let's dry line the room with 2" celotex on the external
50mm. Thats a U value of 0.4, so with 15mm plasterboard at 10, and
wall at 3.5, neglecting cold bridging by studs we can achieve an
wall U value of 0.35. 186sq ft (17.2799654 sq meters) less 2.5 sq
meters of windows nets us 15.2..and the saving in heat will be an
average of 240 W average. Or 2097KWh over the whole year.
Thats for 5 sheets of celotex and 5 sheets of plasterboard..and some
studwork..say 400 quid in all? and a hundred quids worth of skim and
paint..well anyway its WELL under £1000, and at 10p a KWh, it will
£200 per annum. An ROI of around at LEAST 20%.
Similar gains may be expected from doing the same to the floor.
In short even if my figures for energy costs are high, based on
electricity, the gains to be had from drylining are about 20 times as
cost effective as double glazing.
If we add in an insulated floor as well..then our gains are about 234
watts out of the 437..such that all that is left is the window
really..about 63W average...and our walls are now losing just 40
In short we have come from 437.5 watts down to 103W..75% of the
bill has gone. Adding SG might net us a further 40W or so, but so
a decent set of nice lined curtains.
My points are these.
1/. Loft wall and floor insulation represents ROI of up to 30% or
2/. Loft wall and floor insulation on an uninsulated property
up to 70% energy reduction. More if you do it to full building
specs. With a typical figure of less than 10% of wall area and only
factor of two improvement, double glazing represents at best a 5%
saving on an otherwise uninsulated or just loft insulated house, and
probably less than 1% ROI. It is in fact a total waste of money and
never pay for itself..unless you had to replace the windows anyway.
3/. Fitting a new boiler is easy enough..going from a 50% efficient
boiler to an 80% efficient one is a net energy improvement of 37.5%
bills..the ROI will be easy to calculate from your annualised fuel
4/. Let's say our 437W room has two 100W lamps, used an average of 4
hours a day..291.2 KWh per year..and we replace then with two 17W
CFLs..costing a fiver each. So we come down to just 49Kwh per annum.
we have to make good the heat no longer added to the room..well
the net saving IS about £24 on electricity...not bad returns for a
tenner..but mitigated by the fact that we have to add the heat back
the boiler..in terms of saving the planet we don't really save that
after all..as our boiler is not a great deal better than the
generating plant. Still, it's something.
5/. Here's another interesting calculation. Let's say our house is a
bed detached one comprising 8 rooms on two storeys as calculated. so
it's total heating is 8x437 watts. Annualised that is 30MWh. About
to heat then with electricity (and as anyone who has used storage
heaters, in a house like that, thats not far off true). Now you get
about 10KWh per liter of heating oil (and similar for a cu meter of
actually) so at say a 50% boiler efficiency, that's around 5Kwh per
liter..which equates to 6000 liters of oil to heat that house. Again
those of us who have heated houses like that know thats not
That's 1320 gallons..enough to take a nice tidy 45mpg diesel car
miles...let's say you insulate your house and knock that down by
70%..you can afford to run a car for 42,000 miles a year and still be
using less oil.
Makes you wonder sometimes why car fuel is 90p a liter and heating
is 30p a liter.
That actually puts a new 80% efficient boiler into perspective. Say
costs a grand. But puts out 8.5Kw/liter. You save 1500 liters a
or around £450. On an uninsulated house.
On your 1800 liters a year insulated house, you will save just 450
lites, or £150. Not that great a saving..15% ROI.
6/. Wearing a £50 pullover that you replace every year, and knocking
your stat down by one degree, to 18C..saves you 20% of your annual
bill. If its at £1800 a year (30p/l and 6000 liters) and you are a
family of 4, that's £360 a year off your fuel bill for a cost of £200
Of course, once you insulate the house and are running at a mere £540
year heating bill, the savings of £108 are not worth the cost of
(and washing) the pullovers..;-)
7/. One annual trip of 2000 miles by plane (at about 70mpg per
passenger)is peanuts compared with the 12,000 miles you do to commute
your job at 45mpgh, or less in congestion..
8/. Lets say you do 60 miles a day, 200 days a year ..a nice 12,000
mile commute. And you elect to stay at home and work 3 days a week
home. That takes you to 3000 miles a year commute. The direct savings
fuel at 45mpg are 200 liters. About £180 a year..but with motoring
in total running at around £.20 a mile your real savings are nearer
£1800..and since you pay out of taxed income, that's about £3600 off
your gross salary..and £4000 of what you cost your employer..before
cost of office space., heating and lighting, and kit is taken into
account. Probably another £1800 or so. So he could afford to pay you
another £2200 a year to work from home, and you would be directly
better off..so the equivalent to a £4k pay rise to you, and a gain of
about 6 hours a week....240 hours a year on a 200 day working
about 6 weeks extra holiday in gain of leisure hours, to you.
Why ARE we commuting then? No real answer.
9/. What does a hot bath cost? well mine is 1.3 long x .5 wide x .
195 liters. But I take up a lot of that so lets say 100l for a really
good soak. I like my bath to be as hot as I can stand..lets say 45C
we will assume the average incoming water temp is around 14C ..so 39
rise and 100liters is 3900 calories or 16.4 Mjoules. That's getting
for a liter of fuel with a 50% efficient boiler. Gosh. Almost 30p.
Could cost as much as 100 quid a year to have a real soak every day.
10/. Do showers save money and the planet?
Well that depends on how good they are. we know that a mingy electric
shower soaks up 10KW..so on a 6 minute shower thats 1KWh..3.6MJ. Most
decent showers will do at least twice that..a typical combi today
do 30KW..so a 6 minute shower would be 10.8MJ. In short unless you
simply use showers for a quick brush up and are in and out quickly,
don't save you any money or water really at all over a medium bath.
11/. Does an electric kettle half full save the planet? Let's say
kettle is a liter. 2 pints or thereabouts. And the water in it is at
room temp..say 20C because you left it there from the last cup of
coffee. And you make 10 cups of coffee or tea a day. That's 800
kilocalories of heat a day. 3.36MJ. At a 50% fuel to electric
ratio that's almost a 1/6th of a liter. 5p!! almost £15 a year on
boiling!!! so lets say we save half of that directly..30 liters of
a year..In fact we don't, because a lot of the time we are heating
houses and the kettle is part of that..the net gain is probably less.
say 15 liters of fuel a year. about a fiver. Or to put it another way
thats about 3.3 gallons of fuel a year, or 150 miles of road fuel
Taking two days off work saves nearly that. or going to the
at a 5 mile round trip one time less a week saves more.
Why did I taker the time to write all this?
Well..in cam.misc someone complained their gas bill was too high, and
UK.D-i-y, someone wanted to know how much better double glazing was
single glazing..and I really thought.."we get bombarded with green
told to buy CFL's take showers not baths, half fill kettles, buy new
boilers, fit double glazing and not fly"
And yet the reality is that the massive dominant and overriding two
things we do that chew up oil and cost us a bloody fortune, are heat
uninsulated houses, and drive to work every day. And the supermarket
every other day and the kids to school half the year..
The rest is completely irrelevant as long as we don't insulate the
ceilings and floors, and continue to use the car on a daily basis to
an average of around 50 miles a day.