Measuring the U-Value of a Room

[DIYWell]

Is it possible for a DIYer with basic tools to work out the U value of a room?

 

[JohnD]

I used to do it with a piece of paper and a pencil.

I suppose if you wanted to splash out on professional tools, you could buy a calculator and a tape-measure.

 

[DIYWell]

I used to do it with a piece of paper and a pencil.

I suppose if you wanted to splash out on professional tools, you could buy a calculator and a tape-measure.

Wow, what a well thought out and witty answer. If only you had put the effort into being helpful m8.

 

[JohnD]

You mean you don't know how it's done?

you measure the walls, windows, ceiling and floor, decide what they're made of, and look up the U-values of each, then multiply by size in square metres and add them together.

U-value tables are readily available and you can download any number of them off the net.

"U" Value is the coefficient of transmission, i.e., the transmission of heat through the materials, which compose the building's "envelope," or outer shell.


"U" Value has an inverse relationship to "R" Value. For example, a building with material with an "R" Value of R-11 converts to an "U" Value of 0.09 ( 1 divided by 11).

 

[DIYWell]

Thanks.

I'm familiar with the theory, I'm just wondering if there is a relatively easy way to measure the real value rather than calculate the theoretical value.

 

[hotrod]

I'm just wondering if there is a relatively easy way to measure the real value rather than calculate the theoretical value.

Hi DIYWell, you asked about calculating a U-value, this is measured in W/m²K (as I'm sure you're aware). What exactly do you mean by a "real" value?

 

[freddiemercurystwin]

I'm familiar with the theory

Why ask then?

 

[noseall]

Heat loss values are all theory aren't they?

To actually visualise and subsequently quantify, you would need a heat sensitive camera and some pretty special monitoring equipment.

 

[DIYWell]

Yes, looking up the tables and calculating the number is the theory, but it would be nice to see if the theory comes close to the practice.

IR camera will only tell you the temperature and you'd be able to see where the cold spots are, but not much use for a practical U value.

I reckon I could do it with a small heater so I knew what the power input was, thermometer inside, one outside to measure the difference, a still, dry day so the external temperature is relatively constant, let the room heat to a steady state so power in = power out then heat ...

Oh well, perhaps something to ponder over the weekend.

 

[stuart45]

There is a chart you can use to determine the U value of the walls. You need to know the difference between the external and internal air temperatures, and the difference between the internal air temperature and the internal surface temperature to use it.

 

[jeds]

There's not really any such thing as a U-value for a room. A U-value is the amount of heat lost through one square metre of a given component. A room would have at least 5 components: the ceiling, the walls, the floor the window and the door, and all these would have different U-values. Combining the U-values together does not produce one overall U-value.

 

[PrenticeBoyofDerry]

Try this you need an email address to register. But it's free. it might be of use to you but...
www.celotex.co.uk/Other-Resources/U-value-Calculator -

 

[TicklyT]

Or start with your gas bills, and work backwards. From the bill you can work out the amount of heat required over a year, find the average temperature data from the met. office, etc. etc. and see how the figure differs from the calculated value.

 

[Bon]

Yes, looking up the tables and calculating the number is the theory, but it would be nice to see if the theory comes close to the practice.

IR camera will only tell you the temperature and you'd be able to see where the cold spots are, but not much use for a practical U value.

I reckon I could do it with a small heater so I knew what the power input was, thermometer inside, one outside to measure the difference, a still, dry day so the external temperature is relatively constant, let the room heat to a steady state so power in = power out then heat ...

Oh well, perhaps something to ponder over the weekend.

What a ridiculously over-complex waste of time! U-values are used by designers to ensure the heating plant specified is capable. You even add 10% to the final figure for a bit of bunce. A lot of services contractors would have been put out of business by now if the theory didn't work.

If you want to ponder something, you should should study the principles of heat and mass transfer. That will show you the workings of the theory and give you some peace of mind that will save you messing about with a heater.

As for your concerns about the theory working in practice, the CIBSE guides aren't in the habit of dishing out duff information!

Oh yeah, and don't forget to factor in your heat loss due to infiltration as well as your fabric losses (0.33 x No. of air changes/hour x room volume x delta T)

 

[chapeau]

Or start with your gas bills, and work backwards.

Yes, that is a clever 'out of the box' way of doing it.

Unfortunately I suspect the OP will object because you don't include the heat being generated by Fido, so do you include the calorific value of the dog food brought in too?