What is the Best Pipe Insulation for Air Source Heat Pumps?

There is a lot of the wrong information out there when it comes to the right kind of pipe insulation for ASHP, if not intentionally misleading in many cases. This post aims to give you clear, concise and accurate information about the best pipe insulation for air source heat pumps.

The external insulation for Air Source Heat Pump pipework needs the following properties:

• UV Stable / Resistant
• Waterproof / Water Resistant
• 19mm Thick or better of good quality insulation
• Damage Resistant

UV Resistance

OK, so first things first - for the pipework that is going outdoors you need something with excellent UV resistance. A lot of pipe insulation materials are not and will degrade in sunlight. The worst of these is uncoated expanded nitrile rubber - it will be falling off the pipe in 6 months to 2 years if it is not protected in some way (painted, covered or boxed in). The insulation itself is very good but something I say for every insulation is that it is a case of horses for courses.

There is a persisting myth that nitrile is good for outdoor use and the reason behind this is that it was 30 years ago when there used to be a lot more carbon black in the formulations at that time which is a very effective UV blocker. Over time and with increasing focus on performance in case of a fire this is no longer the case so the material cannot be used outdoors without additional protection. That said, a pre-coated nitrile rubber offers a lot of advantages, but more on that later. You can also use materials such as EPDM rubbers (such as HT/Armaflex) which are more commonly used for solar thermal pipework but can do a job here - it is worth noting they are less thermally efficient than nitrile or other closed cell flexible foams so you may need to increase the thickness that you are using.

Water Resistance

Most closed cell pipe insulation materials have good water resistance but not totally waterproof. If you take something like Climaflex pipe insulation (the standard grey foam) then this is actually one of the most water resistant lagging materials you can get without applying an additional protection. It is so water resistant that if you were to soak it in water for 90 days it would only take on 1.5% by volume - it cannot be called waterproof for this reason but it is the next best thing. It can actually be used outdoors if you are looking for a temporary solution, typically it will survive a few years before it needs to be replaced. However, virtually all insulation works by trapping still air - if the material is allowed to take on water then it gradually becomes less efficient and eventually ceases to insulate at all (water is a conductor so wet insulation is literally worse than no insulation as it effectively speeds up heat loss or time to freeze). For this reason materials that are totally waterproof are preferable although the risk of any closed cell insulation getting waterlogged is relatively low.

Quality Pipe Insulation

Don't take it for granted that the product you are buying is good quality pipe insulation - many years ago the UK insulation market had a "never mind the quality, feel the width" attitude to insulation but thankfully we have moved on since then. With that said, many pipe insulation materials for heat pumps do not declare the thermal values for the insulation which is a big red flag; if they do not declare a thermal value then you really don't know how much good the insulation is actually doing. We recommend 19mm thickness of an insulation with a thermal conductivity of 0.035 W/m.K or better (lower).

A thermal conductivity expressed in W/m.K (Watts per Metre, Kelvin) is an expression of energy transfer over a given distance at a given temperature. In other words, this is a constant value for an insulation so if one product is 0.035W/m.K and another is 0.045W/m.K then the lower number is better because it means less energy is being transferred through the insulation. If you have 19mm of a good insulation you save more energy than 19mm of a poor insulation - the question you really need to ask yourself is if the insulation you are using does not declare it's thermal value then is this because they know it is not good enough?

Damage Resistance

Damage resistance is key when your pipework is being used outdoors as it stands to reason that there are more ways for it to be damaged - animal attack for example. Boxing the insulation in is one option and another I have seen work successfully in the past is to run the insulated pipe through another, larger pipe. However, both of these require additional time and materials to work properly. A better option is to use a product with a pre applied plastic skin - this looks neater, is quicker to install and maintains a consistent finish to the install, especially when paired with a good quality matching tape for the butt joints.

Any material that is sold as peck proof or animal attach proof needs to be treated with a certain amount of skepticism - a coating can certainly give a material significantly more protection than a material that is uncoated or merely painted but anybody who lives near the sea (I do to be fair) can tell you that seagulls can cause a lot of damage. A good coating will withstand most common or garden visitors, just beware that they still have their limitations.

Conclusion

With all of the above said, and based on my own personal experience, I recommend the Isopipe TC Solar product that we stock and supply. It is based on good quality nitrile rubber (the Class 0 type) with fully declared thermal values a pre applied, tough, polymeric skin and we can supply either in 2m tubes (no split) or as pre split, self adhesive 1m lengths. Surprisingly this product is still flexible which can help a great deal with tricky installs. As it is a European manufactured product it is made in accordance with EN 13467 - while products manufactured outside of the European Union are not automatically bad they may not be manufactured to the same standards as other products sold in the UK, or around Europe generally, so while you may think you are comparing apples with apples choosing between insulation this may not in fact be true.

I hope that this information helps you but you can get in touch with us if you need more help. We can often provide discounts for larger projects or ongoing supply so feel free to reach out to me directly if you want to discuss this or any other insulation.