Actual u-value measurement


Does anyone know of any low cost tools or tech for measuring building element u-vlaues? I have found these, but as it’s initially a one-off requirement, the subscription model doesn’t work. “Proper” heat flux systems are way to expense to buy.

I’d prefer to try and hack something together to work with e.g. the Zigbee protocol and a Rapsberrry Pi, and I think there’s a lot of knowledge within CC on that front.

I have searched around for such sensors, but with little success


For a one off assessment I would call in an expert with the equipment. I would then interrogate them about methods and kit.

I’ve also wondered about this. It feels like it should be possible to get a reasonable approximation of the U value from the ambient or maybe surface temperature difference on both sides of a medium.

I’ve been looking at the Lee’s disc method as a proxy since it is supposedly good for working out the thermal conductivity of poor conductors - glass and wood are listed as potential candidates.

Still, I’m not sure on the maths involved, nor how to apply it to eg, a wall with cavities.

There’s also a wiki article listing different methods: Thermal conductivity measurement - Wikipedia

I’d be keen to keep in touch about this if you’re actively pursuing it as a DIY thing.

Probably most saliently to where we’re talking, I’d also wonder if a little fundraising for carbon coop might be able to buy a relevant bit of gear.

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Ultimately- solution depends on what you are trying to achieve. What is the question that needs answering?

Re Lee’s method, I think the hard and software would be do-able, but removing parts of the fabric as samples may be a stretch for most other homeowners (if that was the idea) :slight_smile:
The cheapest sensor I found is $45, but hey also do educational kits that come with a (bakers) dozen workshops, so maybe that would be useful for Carbon Coop’s next generation of Retrofit Coordinators?

I am really interested in this @John_Hackett but it would be lower down the list of things to do, as hopefully we’re starting our retrofit soon (a long, delayed story). But v happy to keep in touch about it.

Q. What is the actual in-situ u-value of a specific wall/roof/floor?
Rather than the general, often safe/pessismistic value for a given material.

My own example- our hallway was cooler than the rest of the house and the assumption was that the uninsulated wall between hall and garage was the cause. I measured temperature on either side of the wall in the morning and evening for a couple of days and averaged the difference (first thing in morning and late evening –“steady state”). I converted to Fahrenheit, measured the wall area in feet and multiplied it by the standard U value for a solid brick wall to give a BTU/hour heat loss - through ONE sq ft for ONE degree change. Alarmed at the result I got, I insulated the wall (cold side) and the temperature difference was eliminated and my energy bill was reduced.

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I like your method but be warned that the SI unit U-value has some complex relationship with the American U-value calculated in °F and ft2. The unit used in this country is the Standard International one. The U and R values are very different.

Very true Tim, but it made me act to resolve a real issue and we are benefitting now.

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This is not exactly what you are asking for, but it might be helpful. If you want the peak whole house thermal loss rate (kind of like the total u-value), you can use you annual heating bill and your location, as described here:

Maybe you can divide this across your rooms to get an estimate for each?

This is a reasonable article for whole house energy requirements and as specified, calculating heat pump (or even boiler :-1:t2:) size. For radiator size you need to do a room by room calculation, unless your entire living area is open plan.

Edit: using the annual gas to area ratio I managed 53.7kWh/m2/a. Not quite the AECB standard and over double my target of the EnerPHit standard.
I disagree with the author that EnerPHit is best possible for a retrofit but for many it is the best practical.