Determining heat loss

[Timothy Murphy]

Is there any scientific way of determining the heat lost through ceiling, wall, windows, etc?

[Osprey]

There is a BS method for detremining heat loss ...to obatin U-values. Seach the BSI site for 'u-value'

[TheOldFellow]

Yes, get the U-value of the materials, multiply by the area, then by the temperature difference.

I have a spreadsheet that I made for my bungalow. If you want a copy I'll email it directly. IANAHE (I am not a heating engineer)

R.

[dom]

Described in detail with worked examples - in Part L of the Building Regulations.

[dom]

Here:

[tim.....]

I imagine that for a wall now covered in plaster, this is the hard part :-(

tim

[ransley]

Get an energy audit. a pro to do a heat load calculation, a blower door test to show air exchenges per hour and a Thermal image of the home. You can start by telling us how much and what type of attic and wall insulation you have, but if what a pro says if followed you might save 50% on your bills if things are in poor shape.

[TheOldFellow]

To some extent, but if it's brick with a cavity built between, say 1960 and 1975, and there is no trace of back-filling of cavity foam/fill, then it's a good bet that it's a standard brick cavity with plaster construction for an outside wall. Most standard constructions have reasonable rule-of-thumb U-Values available. If you just used a U-value of 1 for all uninsulated outside walls you would not be far out.

These are what I've used, and I'd be interested in a better source:

Material U-Value=09

11=E2=80=9D Cavity Wall (not insulated) 1=09 11=E2=80=9D Cavity Wall (Rockwool) 0.6=09 3=E2=80=9D Single Brick Wall 2.2=09 Wall piercing (e.g Ventaxia) 5=09 Solid Concrete Floor 0.8=09 Ceiling T&G Boards 1.7=09 Roof Pitched with Felt 100mm 0.3=09 Roof with 250mm Insulation 0.07=09 Roof with 50mm Insulation 0.26=09 Window single glazed 5=09 Window 20mm low-e 1.7=09 Window Minimal double glazed 2.9=09 Door External timber 2.4=09 Internal Door 1.8=09 Internal Stud Wall 1.8=09 40mm Triple Polycarbonate roofing 1.4=09

I imagined, perhaps incorrectly, that the OP was looking for an Engineering, rather than Scientific method. If he really wants a scientific method, he'll need to find the U-Value by experiment. Get out core drill. Take statistically valid number of sample cores to laboratory...

R.

[The Natural Philosopher]

yes. ;-)

[The Natural Philosopher]

Not as long as you know what is underneath.

[tim.....]

Unless you put the plaster on (or watched someone else do so), why would you know what was underneath?

[Rod]

Do you know how much energy it takes to heat it? Then you know pretty well how much it loses!

[The Natural Philosopher]

Gosh. I see what you mean. It might be marshmallow. Or balsa wood.Or wet limp sphaghetti, or anything else the architect specified and the building inspector allowed.

Do you spend your life opening te packets in the supermarket to see whats inside?

[Timothy Murphy]

Thanks. That was the only one of the many replies that seemed to me to come anywhere near answering my query.

First of all, the building is a 150-year old single story detached cottage.

I think the walls are a mixture of stone and brick, plastered over.

When I said "heat lost through ceiling, wall, windows, etc" I was thinking of the individual items, not the total.

It seems to me that calculation from U-values is more or less useless in such a case.

There is fibre-glass insulation - about 4 inches thick, I would estimate - in the attic, but it is very difficult to get up there, as there is only 50cm from the joists to the centre of the roof, and the sides of the roof come down over the rooms below.

I did ask a supposed expert for his opinion, but I was not convinced by his estimates. He said that 30% of the heat would be lost through the walls, and 15% through the ceiling, which I am almost certain is wildly wrong.

The reason why I was asking was because one man I consulted said that the best way to improve the insulation in the attic would be to re-lay the slates (they are not currently felted) and add insulation at the same time.

His price for doing this was 7,000 euro, which was half the estimate for the same work given by another roofer.

I'm quite attracted to this solution, as felting the roof seems to me to be a sensible thing to do in any case - also some of the original slate tiles have been replaced with asbestos tiles.

But it would be nice to have an estimate for the amount of heat that would be saved by this.

Incidentally, a friend of mine had an "energy audit" done by a supposed professional, who charged 700 euro and basically said she (the owner) needed to add more attic insulation, which I would have told her for 7 cents.

[george (dicegeorge)]

There was a kind of temperature gun recommended on this group months ago but i cant remember what it was - you point it at a wall or ceiling and it somehow gives a temperature reading which would be good for finding heat leaks i think...

i'm considering sticking kingspan from inside my bedroom onto the ceiling, with the vapour barrier downwards, a lot easier than fitting between the rafters i think...

But first to stop more draughts...

[g]

[The Natural Philosopher]

where are you? could be clunch, or hard stone. Makes a difference..

But at 150 years old its likely to not have a cavity. How thick are the walls?

There are standard U values (watts lost per square meter per degree cetigarde temperature differential) for all those items.

Not at all.

A typical single glazed window of a U value of 6, with a one square meter area,willlose 6W for every dgree warmer it is inside than out, for example,

You can add all the element losses up to get a total loss.

Better than nothing, but only a small area of the total heat losing surfaces.

Well in an old house thats not far off, with about 50% lost in draughts.

Thats not a bad idea but felting won't solve a lot.

If the roof needs it. go for that, felting is more windproofing than anything else. And wind does reduce the efficacy of rockwool.

You might as well put as much of that in the roof cavity - up to 8" or so laid between then acrosf the josts - as you can. It's cheap.

Not very much sadly.

Look when I did some back of envelope calcs the worst thing in most old houses is ill fitting doors and windows and suspended wooden floors with an airgap underneath, also chimneys if you aren't using fires. These allow wind to whistle through.

I ghad an old slated single brick cottage, and it was diabolical. My first step was to lift the carpets and nail hardboard all over the gappy pine flooring. That made a huge difference at almost no cost at all. Then I put foam strip on all the doors. That was again a mighty improvement.

The landlord then fitted DG windows..to be honest they made a huge difference to the draughts, but not a lot otherwise. DG is not worth the costs if the existing windows are well sealed and fitted with thick curtains.

I was able to improve the kitchen a bit especially from the condensation point of view with 3mm cork sheet on the outside walls.

But the next step would have been drylining the walls with insulation, and the rooms were too small for that, and anyway, I bought a house and moved out.

The reason why loft insulation is a Good Thing. is that there is nothing bu a 15mm piece of plasterboard between the room and the icy attic/loft. That loses a lot of heat so a small amount of insulation like you have makes a big difference to the upstairs rooms.

Once that's done however, and you have done the draught proofing, the major losses turn out to be the walls, largely because there is more wall than window,ceiling or floor in most houses. And its often solid brick, which is a pretty fair conductor of heat.

The k factor of brick is about 1 on average, so that means that e.g. 9" of brick (200mm) is 1/0.2 = a U value of about 5, which is very similar to a single glazed window. Stone might be twice that.

Recommended U`values for walls are 0.45,so something like ten times better than a single brick wall.

glass fibre or styrene foam has a U value of about .03 per meter so

100mm of that does the trick easily (U value about 0.3). As does about 50-60mm of celotex or kingspan.

Note that even just 3mm of styrene foam..has a U value of 1, thats 6 times better than a 9" brick wall.

Which is why my cork tiles worked. cork is not as good as styrene foam, but its a pretty decent insulator.

What you need to do is calculate the losses from the house SIMPLY..not exhaustively like the engineers will.

work out the ceiling area, and assume a U value of about 1, with that sort of 4" of fibre.

work out total windowand door area, and multiply that by around 5, if single glazed,

work out total floor area, and if sold floors, go for around 3 as an average U value, or about 6 if suspended wood.

Work out the walls, area and thickness. Take the area and divide by the thickness (in sq meters and meters), and that is our last number.

Now this is not precise, but chances are one o the numbers will be much bigger than all the rest. Thats the one worth tackling.

The sum of all those numbers times the difference between your internal temperature and outside - say 25C for 20C house and -5C outside, is about your peak heat requirement in watts. Make your boiler at least

25% over that.

rough and ready calculations like these are extremely useful. They show you where the most savings are to be had.

My guess is, its your walls that are the most losses. After the draughts. Spend the 7000 on dry lining.

[BruceB]

I have used this heat loss calculator which worked fine and allowed some what-ifs.

[Alan Braggins]

I recently got one of these (it was cheaper at the time):

proper thermal imager would be a lot more effective at finding cold spots where insulation is missing, but be a lot more expensive. The thermometer can give some idea though.

[Timothy Murphy]

If they are stone, they would be granite blocks. The building was the wash-house and later nursery for the orphanage next door, which is a large granite building.

Well, that is based on an actual measurement, the difference in temperature between inside and outside. I'm sure that would give a reasonably accurate measure of the heat-loss through the window.

I'm reluctant to do anything like that, because I think it would dis-improve the look of the cottage inside.

[The Natural Philosopher]

About the m,ost thremally condcting rock there is. K value abou 2.6.

Well its your choice, aesthetics or heating bill.

Do you have exposed brick inside or summat?

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