Insulating Pipes in the Garage

We had a new condensing boiler installed in Summer 2017, complete with new radiators and connecting pipes. The new connecting pipes are mostly plastic and, to simplify installation, the garage was used to route some of the pipes. My simplistic take is that the other pipework, mostly in the ground floor ceiling (and a little on internal walls or behind skirting boards), is helping to warm the house and so the fact that it is not insulated does not really cause significant losses. However, the pipework in the garage, was simply raising the temperature of the garage.

 

Situation before insulation:

Pipework routed through the garage: 

• 13.8m of 28mm  diameter pipework
• 2.3m of 15mm  diameter pipework
• 8.4m of 10mm diameter pipework

When hot water was flowing to these radiators the pipework was hot to touch. 

 

After insulation:

28mm Pipes with Insulation	10mm Pipes with Insulation

 

The external surface of the insulation is very slightly warm to touch when water is flowing to the radiators. I would expect that the radiator temperature is a little warmer now, but I could not detect this by hand.

 

Shopping list:

• 2x 3pack x 2m of 9mm thick insulation for 10mm diameter pipes. Note: most insulation that I found for smaller pipes was thinner than for larger diameter pipes; I am not sure why given that the physics, I think, is the same. I chose the thickest that I could find.
• 13mm thick insulation for 15mm diameter pipes.
• 19mm thick insulation for 28mm diameter pipes.
• Pipe clips (new ones to allow space between pipes & the wall for insulation)
  
• Spacer/washers: the pipe clips for smaller pipes, did not allow enough space for insulation at the back, so spacers were requires so that the pipe sat a few extra mm from the wall).
• Duck tape (to hold smaller pieces of insulation, eg at corners and joins)
• Total Approx £120

 

Doing the work:

This took a total of about 10 hours at the weekends, mostly in replacing the pipe clips to give space for insulation behind the pipes - better insulation and the insulation holds on the pipe without (much) tape.

 

Estimate of saving and payback:

This is hard. This was the only new energy saving measure that I took before the winter of 2021/22 and in 2021/22 we saw a 36% (£980) saving in gas usage over 2020/21. However, I am not convinced that insulating a few pipes gave all of this saving. Perhaps lockdown during the pandemic causes a spike in usage in 2020/21 or 2021/22 is unusually low and usage will rise back up in 2022/23...

...I will analyse the data for 2022/23 and see if I can get a better understanding of the energy saved and payback over a longer period (future blog post). However, given the low cost and the dramatic drop in pipe temperature, I would be surprised if payback is very long.

 

Can I Calculate the Energy Saving?

This website  (https://modbs.co.uk/news/fullstory.php/aid/615/Clear_thinking_on_insulating_plastic_pipes.html>) gives a range for the heat conductivity of plastic pipe of 0.16 to 0.22 W/m.K. I am a little dubious about this as heat loss is surely related to surface area and my pipes range from 28mm diameter down to 10mm diameter, so must have a surface area range of around 3:1. However, using an average of:

• 0.2W/m.K for all pipes (irrespective of diameter)

and assuming:

• Uninsulated: a temperature drop of 60degC across the plastic pipe wall, from flow temperature (set at 70degC) to average room temperature (guessed at 10degC)
• Insulated: zero temperature drop on the plastic pipe wall (ie all the temperature drop is across the insulation)
• Gives a total saving in heat/power loss of ~300W, when the pipes are hot

I mapped this across the year with the following assumptions:

• Heating on from 6am to 10pm = 16 hours (some days we keep it on later, but we also turn it off when out)
• Duty cycle (& this is a real guess) of 50% in winter (4 months), 25% in Spring/Autumn (2months+2months), 10% in summer (4months)

Gives an annual saving of approx. 500kWh, or ~£35, at the £0.07/kWh charge that I am using from August 2023.

Given how hot the pipes were then I can believe the 300W (1/3 of a 1 bar fire). However, given all the assumptions I think that there is quite an error band in this calculation, especially in the average pipe thermal conductivity and the duty cycle that I used to map this onto annual energy savings.

 

And Finally:

In writing this post I have realised that the pipework for the hot water cylinder is all under the 1st floor boards (above the ground floor ceiling). Perhaps there would be a case to insulate these pipes as they heat up the house in summer (a future project and blog entry perhaps).