Replacing the UV-damaged foam lagging (insulation) on your heat pump's refrigerant pipe lines is one of the few heat pump maintenance tasks a competent homeowner can tackle themselves — provided you stick strictly to the lagging itself and don't interfere with the refrigerant pipes, electrical connections, or any sealed components. Here's what you need to know before you grab a Stanley knife.
Why Pipe Lagging Matters
The insulated tubing that runs between your outdoor unit and indoor head unit protects the refrigerant lines from heat gain and condensation. Over time — especially on the sections exposed to direct sunlight — the foam pipe lagging (also called pipe wrap or pipe insulation) degrades, cracks, and crumbles. Once it fails, your heat pump works harder than it needs to, your power bills creep up, and moisture can cause corrosion or mould issues around the pipework. Replacing damaged lagging promptly is good maintenance practice and supports the energy efficiency goals outlined by Energywise.
Is This Restricted Work?
This is the critical question. In New Zealand, refrigeration and heat pump work involving refrigerant is restricted work under New Zealand law and must only be carried out by a licensed tradesperson — check with WorkSafe NZ or EECA for the applicable regulations. Similarly, any work on electrical connections is restricted under the Electricity Act and must be done by a registered electrician (check EWRB).
However, simply removing and replacing the foam lagging on the outside of the pipes — without cutting, bending, disconnecting, or pressurising the pipes themselves — is generally considered routine maintenance, not restricted work. You are not touching the refrigerant circuit or any electrical components. That said, always use common sense: if the pipes look damaged, kinked, or corroded underneath the old lagging, stop and call a licensed heat pump technician.
What You'll Need
- Closed-cell foam pipe insulation (also called pipe lagging or armaflex-style tube insulation) — sized to match your pipe diameter. Common sizes for residential heat pump lines are 12 mm, 16 mm, or 19 mm bore. Measure the outer diameter of your pipes before buying.
- UV-resistant self-amalgamating tape or purpose-made UV-protective pipe wrap tape for the outer layer on exposed runs
- Foam-compatible adhesive or self-sealing lagging with pre-applied adhesive
- Sharp utility knife or scissors
- Cable ties or UV-resistant zip ties
- Gloves and safety glasses
You'll find suitable pipe insulation and UV-resistant tape at Bunnings or Mitre 10. Look specifically for closed-cell foam (not open-cell) as it resists moisture absorption. If the pipes are in direct sun, the foam alone won't last — you must add a UV-protective outer wrap or tape, as bare foam degrades quickly in NZ's UV environment.
Step-by-Step: Replacing the Lagging
1. Turn Off the Heat Pump
Switch the unit off at the controller and at the isolating switch. You are not working on electrical components, but it's good practice.
2. Remove the Old Lagging
Carefully cut away the old foam using a utility knife. Take care not to nick, kink, or scratch the copper pipes underneath. If the pipes are wrapped in a bundle with electrical cables (common in NZ installations), be especially careful.
3. Inspect the Pipes
Before fitting new lagging, check the copper pipes for corrosion, green patina, kinks, or any signs of oily residue (which can indicate a refrigerant leak). If you see any of these, do not proceed — call a licensed heat pump installer. You can find qualified local technicians on tradedirectory.co.nz.
4. Fit the New Foam Lagging
Slide or slit the new foam tube over each pipe. If using slit lagging, apply foam-compatible adhesive along the seam and press firmly. Butt joins tightly together — gaps let moisture and heat in.
5. Apply UV Protection
On any section exposed to sunlight, wrap the foam with UV-resistant self-amalgamating tape or purpose-made pipe wrap, overlapping each layer by about 50%. This outer layer is what actually stops UV from destroying the foam again.
6. Secure and Tidy
Use UV-resistant cable ties or clips to keep the lagged pipes tidy and off surfaces where they could trap moisture.
Choosing the Right Materials
| Feature | What to Look For |
|---|---|
| Foam type | Closed-cell (e.g. Armaflex-style or equivalent) |
| Bore size | Match to pipe OD — measure before buying |
| Wall thickness | Minimum 13 mm for refrigerant lines |
| UV protection | Self-amalgamating tape or UV-rated outer wrap |
| Adhesive | Foam-compatible, not solvent-based |
When to Call a Professional
Call a licensed heat pump installer or refrigeration technician if:
- You find corrosion, kinks, or oily residue on the pipes (possible refrigerant leak)
- The lagging is damaged right at the wall entry point or at the unit connections — these areas are tricky and close to electrical and refrigerant components
- You're unsure of the pipe sizes or the installation looks non-standard
- The outdoor unit itself looks damaged or the system isn't performing well
For any work involving the refrigerant circuit, electrical isolators, or the units themselves, you must use a licensed professional. Check MBIE Building Performance for guidance on what work requires a building consent, and always confirm with your local council if you're unsure.
A qualified heat pump installer can also check your system's overall performance while they're there — well worth it if the unit is a few years old. Find a local installer on tradedirectory.co.nz.
ISO 9001
