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Seal the Deal: Don't Let Your Heat Pump Leak Energy

David Smith · 2024-08-13T11:05:37Z

In recent years, one critical aspect of air source heat pump installations has often been neglected: external pipe insulation. As the demand for energy efficiency increases, the importance of using the best possible external insulation for ASHPs cannot be overstated. So let's delve into why high-quality external insulation is essential and what characteristics make insulation effective and reliable. Water Resistance Moisture can drastically reduce the thermal efficiency of insulation. When insulation becomes wet, its thermal conductivity increases, leading to energy loss and the deterioration of the material. Therefore, insulation with high water diffusion resistance is crucial. Additionally, sealing all joints and gaps is essential to prevent water ingress through capillary action. If the insulation is not protected and every joint and gap is not sealed correctly, efficiency is seriously compromised. Optimal Insulation Efficiency The primary function of insulation is to minimise thermal loss. This requires materials that fit well without being compressed, as squeezing insulation into tight spaces can reduce its effectiveness and cause thermal bridging. Ensuring that the insulation is properly clipped on the outside and sealed around pipes and fixtures is vital to maintaining efficiency and preventing moisture penetration. The issue is exacerbated when using standard plastic trunking designed for smaller air conditioning pipework. For instance, the typical 140mm trunking hides multiple issues because the two insulated pipes have to be squeezed in to fit, reducing insulation efficiency and potentially causing thermal crossover that can affect the heat pump’s operation. What's more, installers using thinner wall thicknesses than the 19mm standard compromise insulation further. Since it is impossible to clip on the outside of the insulation correctly, many installers resort to clipping the pipework first and then insulating it, using tie wraps to hold the insulation together around the clips. This method leaves gaps and makes it difficult to ensure a consistent seal, reducing the system’s overall efficiency. UV Protection and Air Contamination Resistance External materials are subject to degradation from UV rays. Insulation must have built-in UV protection to withstand outdoor conditions over time. Furthermore, in areas with air pollution, such as near factories or busy roads, insulation needs additional protection to prevent contamination that can impair its function. This level of protection should be present out of the box, as adding UV protection during installation in varying weather conditions is impractical and often ineffective. Through-Wall Sleeving When pipes pass through walls, sleeving protects the insulation from damage and prevents pests from compromising the system. Proper sleeving and sealing ensure that the integrity of the insulation is maintained, thereby preserving the overall energy efficiency of the building. Standard shrouds on plastic trunking are often not large enough to cover two separate insulated pipes, leading many installers to use a 4-inch core and soil pipe. This approach is problematic as it is not waterproof, allowing moisture to enter through joints and gaps, creating a microenvironment that can never dry out, further degrading the insulation. All-Weather Installation Capability Professional installers often work in varied weather conditions. Therefore, insulation products must be easy to install regardless of the weather. This requirement ensures that installations are not delayed and that the insulation performs as expected in both extreme heat and cold. Products must be designed for general weather conditions to help the professional installer complete the job efficiently and effectively. Sealing of Joints and Gaps To maintain efficiency, all joints and gaps must be meticulously sealed. Proper sealing prevents thermal leaks and moisture ingress, which can undermine the insulation’s performance and longevity. The insulation products need to support easy sealing, ensuring that every joint and gap is closed, including those through the wall. If plastic trunking large enough to house the insulation correctly were available, it would need to feature high water resistance, be sealed on all joints, and clipped externally. Ease of Maintenance Regular maintenance is essential for sustaining the efficiency of ASHPs. This includes inspecting and maintaining external insulation and ensuring that all joints remain sealed. High-quality insulation products should facilitate easy maintenance, helping to ensure long-term performance and reliability. Annual services on heat pumps and systems must include checking the external insulation and all joints to maintain and protect the system’s efficiency and all external products. Closing Thoughts Investing in high-quality external insulation for air source heat pumps is crucial for maximising energy efficiency and protecting the system from env...

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Tim441

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25/09/2025 2:24 pm

@allyfish hopefully not to rodent taste too 😬

What make is the insulation?

Listed Grade 2 building with large modern extension.
LG Therma V 16kw ASHP
Underfloor heating + Rads
8kw pv solar
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Tim441

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25/09/2025 2:26 pm

@editor I'll try and keep a little faith...

A few rough edges but nothing major

🤔

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Old_Scientist

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25/09/2025 6:24 pm

I'll go with the standard grey open cell foam insulation you see indoors (as it's protected from UV), with the normal 45deg cut corners. Surely they cannot get that too wrong, can they?

Samsung 12kW gen6 ASHP with 50L volumiser and all new large radiators. 7.2kWp solar (south facing), Tesla PW3 (13.5kW)
Solar generation completely offsets ASHP usage annually. We no longer burn ~1600L of kerosene annually.

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Mars

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25/09/2025 7:23 pm

Interesting. I'll let you all decide.

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bontwoody

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25/09/2025 7:43 pm

What size are those plastic pipes Mars?

House-2 bed partial stone bungalow, 5kW Samsung Gen 6 ASHP (Self install)
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Mars

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25/09/2025 7:44 pm

@bontwoody, not big enough (an excellent spot) 😉

This post was modified 1 month ago by Mars

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Tim441

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25/09/2025 7:44 pm

@editor yep... pipe size is more of concern maybe?

Insulation can certainly be improved!

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JamesPa

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25/09/2025 7:52 pm

Posted by: @editor

↑

Interesting. I'll let you all decide.

Not sure what we are looking at, other than evidence of an installer who says 'here is a hole, let's shove everything inio it'

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

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Mars

(@editor)

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25/09/2025 7:54 pm

Also loads of water ingress… the foamy insulation is damp, which leads to more unnecessary (and completely avoidable) heat loss.

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Transparent

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26/09/2025 2:17 pm

My first concern is that the hole through the brickwork doesn't appear to be sleeved.

There should be an outer casing which takes the weight of the wall above.
That allows the inner pipes to move freely as they expand/contract with temperature.

To achieve that, all those existing pipes and electrical connections would need to be drawn out.

The hole should then be bored out with a TCT/Carbide core bit of an appropriate diameter for the sleeve.
You don't need diamond bits to go through brick. It's 'soft'.

The hole needs to slop downwards to the outside at around 5°.
Any rain or condensation will then not enter the house.

The sort of sleeve you'd be looking for would be a 110mm orange (underground) soil pipe.

That will leave enough space for pipe insulation to continue straight through the wall.

The best person to get this right is the home-owner.
A DIY approach is preferable because you'll care about getting it right !

Save energy... recycle electrons!

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JamesPa

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26/09/2025 4:39 pm

Posted by: @editor

↑

Also loads of water ingress… the foamy insulation is damp, which leads to more unnecessary (and completely avoidable) heat loss.

And mice or other pests given the gaps.

4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.

👍

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Mars

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26/09/2025 8:46 pm

We have a lot of work ahead to get this done properly. All valid points above.

This post was modified 1 month ago by Mars

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