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Discuss Heat loss from pipes in the Central Heating Forum area at PlumbersForums.net

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doitmyself

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1,877
Many heatloss calculators make an allowance of about 5% for the heat lost from uninsulated pipes. So, in my case with 13kW of rads there would be 650W lost from the pipes.

If you search for "heat lost from uninsulated copper pipes" you will come across a lot of info on the subject. But they all give a result similar to this:

Flow Temp 75C, Room Temp 20C = 45.31W/m (15mm); 60.41W/m (22mm)
Return Temp 65C, Room Temp 20C =34.85W/m (15mm); 46.46W/m (22m)

Assuming the hidden pipes in my house follow the shortest route, I estimate that there are 54m of 15mm and 68m of 22mm. (That's total - flow plus return). A quick calculation gives the following heat loss from the pipes:

15mm = 2164W; 22mm = 3634W. Total = 5798W!!!

That's nearly 10 times more than heat loss calculators suggest.

Can anyone explain the discrepancy?

(Yes, I know that the heat isn't really lost as most of it is within the insulated envelope of the house so only the heat from pipes under the floor or in the loft is 'lost', but that's irrelevant to my question.)
 
L

lame plumber

mmmmmmmmmmmmmmmmmmmm, eeeeeeeeeeeeeeeeeeerrrrrrrrrrrrr, dum dee dum dee dum ,nope, never worried me, as the heat is still warming the home, but I am an old dinosaur......... :)
 
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leethegasman

Gas Engineer
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478
Used to be 10 degree loss over radiator and 1 degree loss in pipework so those figures look a little high.
 

Sparkgap

Messages
350
According to my trusty CIBSE guide, horizontal copper pipes (tarnished) in ambient air loses 32 & 25w/m (for 15mm flow and return) and 43/33w/m for 22mm F&R), but that is assuming they're in free air. If in the floor void it will be less as the ambient temp will increase. Total comes to about 4.1kW.
 

doitmyself

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1,877
Used to be 10 degree loss over radiator and 1 degree loss in pipework so those figures look a little high.
The 10 degree is obvious, I wonder where the 1 degree came from

According to my trusty CIBSE guide, horizontal copper pipes (tarnished) in ambient air loses 32 & 25w/m (for 15mm flow and return) and 43/33w/m for 22mm F&R), but that is assuming they're in free air. If in the floor void it will be less as the ambient temp will increase. Total comes to about 4.1kW.
Not being a CIBSE member I don't have access to that guide. I have learnt that horizontal and vertical pipes have different heat losses and that where several pipes in close proximity, this has to be taken into consideration. Location is obviously relevant but there's no available data on the effect. Additionally, tarnishing is never mentioned; obviously it affects the emissivity of the copper. I must do more research.

4.1kW is still a lot more than the 650W (5%) that calculators like Stelrad Stars suggest.
 

chris watkins

Esteemed
Plumber
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5,073
The 5% is known as transmission losses and any program will assume that the installation will be complaint with Part L i.e. all pipes not in the thermal envelop or in voids will be insulated to required standard.
All the rest will as you say contribute to the heating of the building.

Your calculating steady state losses from pipes (just like rads or pipe coils).

BTW you don't need to be a member of CIBSE to get a copy of the Domestic Heating Design Guide ISBN978-1-906846-35-0 well worth the £25 - 28 price tag.
 
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doitmyself

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1,877
The 5% is known as transmission losses and any program will assume that the installation will be complaint with Part L i.e. all pipes not in the thermal envelop or in voids will be insulated to required standard.
All the rest will as you say contribute to the heating of the building.
That makes sense. If I use the data in Table 5 of the Domestic Building Services Compliance Guide the max permitted loss from 15mm pipe is 7.89W/m and 9.12W/m from 22mm pipe. Based on my pipe lengths, this would give a total loss of 1046W or 8%.

My house was built in the 1980's. I wonder what standards applied then?

Your calculating steady state losses from pipes (just like rads or pipe coils).
Got you.

BTW you don't need to be a member of CIBSE to get a copy of the Domestic Heating Design Guide ISBN978-1-906846-35-0 well worth the £25 - 28 price tag.
That's OK if you are in the trade; but I'm was just curious and can't justify spending £28 out of my pension. Pity the Guide is not available as a PDF.
 

doitmyself

Messages
1,877
I recommend this site Heat Loss from Uninsulated Copper Tubes Lots of very useful stuff there.
There are also other pages with losses from pipes with insulation of various thicknesses.
Thanks for the link; I know the site well and often refer to it. Pity it's American and tends to work in imperial measures.

I did a bit of digging and the oldest info I can find is the 1995 edition of Part L which says that the pipes only need insulating if they do not contribute to the heating requirement. Otherwise insulation with k= 0.045 W/mK and thickness same as pipe diameter (up to 40mm) should be used. That gives a heat loss of 11.3 W/m for 15mm and 11.6 W/m for 22mm.
 
J

JCSPLUMBING

Its not enough to care about in a domestic property. Like you say it's in the thermal envelope. However under suspended floors you must insulate the pipes.
 

chris watkins

Esteemed
Plumber
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5,073
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chris watkins

Esteemed
Plumber
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You can't expect me to read all your posts doit, I just sore you quoting from the 1995 Part L in post 9 & thought you needed updating.

I still don't understand what your post is aimed at ?

but agree there is a sad lack of compliance born out of no checks by the Building Control police.
I still see so many installations with no insulation on the pipes around the cylinder let alone the primaries or pipes in voids, it only costs a couple of quid to put on but over the life of the installation would save far more than all these fancy controllers.

PS I don't think it is difficult to follow i.e. look up fuel type then new or updating system?
 
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doitmyself

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1,877
You can't expect me to read all your posts doit, I just sore you quoting from the 1995 Part L in post 9 & thought you needed updating.
I appreciate the thought. :wink_smile:

I still don't understand what your post is aimed at?
If you mean post #12, I just thought you should know that I was aware of the latest guidance. I was just quoting the 1995 version as that was the oldest one I could find when searching for the regulations applicable when my house was built (mid '80s).

there is a sad lack of compliance born out of no checks by the Building Control police.
Isn't it now supposed to be self-certified by the installer?
 

chris watkins

Esteemed
Plumber
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5,073
If you mean post #12, I just thought you should know that I was aware of the latest guidance. I was just quoting the 1995 version as that was the oldest one I could find when searching for the regulations applicable when my house was built (mid '80s).

No sorry what I meant was Thread not Post. Why are you interested in heat loss from your pipework ?

Isn't it now supposed to be self-certified by the installer?

Precisely No policeman!!!
To self-certifie you have to belong to a scheme which means paying a few hundred £ every year & even then BC are not interested. How many of of the guys & girls on hear have done that for Part G let alone L, H, F or P almost none I bet (& to be honest who can blame them).

So we have to rely on them to both find out what is required & then to do the right thing like fitting that low cost bit of insulation to the pipes that got me started on this rant in the first place.

What might be good Mr doit is if you done some investigation & then made a freedom of info request, asking just how many of this nations Plumbing & Heating engineers belong to these schemes & even more interesting how many notification are made against the estimated work being carried out.

It might highlight just how ineffective & pointless this Law is.
 
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doitmyself

Messages
1,877
No sorry what I meant was Thread not Post. Why are you interested in heat loss from your pipework ?
That's a long story, which goes back nearly 10 years; but curiosity really.

It all started when I had cavity and loft insulation installed. I was curious about how much it would reduce the heat loss from the house. That was fairly easy to calculate, but one thing led to another and I ended up with a drawing showing the rads and estimated routes of the pipes. I used this info to calculate the index circuit, but then realised that I needed to take the heat loss from the pipes into account. The only data I could find was for pipes in the open air, so I used that and had a shock when I calculated pipe losses of nearly 6kW. That was obviously wrong, but I couldn't see where; as far as I was concerned the pipes were in open air, even if they were under the floor or in a riser between floors. Of course the pipes could have benn insulared, but none of those visible were, so I assumed none were.

If I use the latest advice and assume all pipes are insulated I get a loss of 1046W from the pipes. This is 8% of the total rad output, but 17.5% of the heat loss from the house.

To self-certify you have to belong to a scheme which means paying a few hundred £ every year & even then BC are not interested.
I suspect BC are only interested in large new build developments as they get a fat fee for monitoring them.

What might be good Mr doit is if you done some investigation & then made a freedom of info request
Don't tempt me. :wink:
 
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