Yes, in most cases a homeowner can seal the wall penetration hole left by a heat pump installation — it's not restricted work under NZ law, and with the right materials it's a straightforward job. That said, doing it properly matters: a poorly sealed penetration can let in moisture, cold draughts, insects, and even allow water to track inside your wall cavity, causing long-term damage. Here's what you need to know.
Why Sealing the Penetration Properly Matters
The hole through your wall carries the refrigerant pipes, electrical cable, and drain hose between your indoor and outdoor heat pump units. It's typically 60–80 mm in diameter. Left unsealed or poorly sealed, it becomes a weak point in your building envelope — allowing:
- Moisture ingress, which can lead to mould and rot inside the wall cavity
- Draughts, reducing the efficiency of your heat pump and home insulation
- Insects and rodents entering the wall space
- Water tracking along the pipes into the wall if the hole isn't pitched correctly
Under the NZ Building Code, clause E2 (External Moisture) requires that penetrations through the building envelope are adequately weatherproofed. While sealing a heat pump hole yourself doesn't require a building consent, the result still needs to meet this performance standard.
What You'll Need
Before you start, gather the following:
- Pipe sleeve or wall sleeve — a purpose-made plastic sleeve that fits around the pipes and fills the hole neatly (available at most hardware stores)
- Exterior-grade sealant — a flexible, paintable, UV-resistant sealant such as a silicone or polyurethane product suitable for exterior use
- Foam backer rod — for filling larger gaps before applying sealant
- Pipe wall cover/escutcheon plate — a decorative cover that clips over the pipes on both the interior and exterior sides
- Safety glasses and gloves
You can find suitable products at Bunnings or Mitre 10. Check the sealant manufacturer's datasheet to confirm it's rated for exterior use and compatible with your wall cladding material.
Step-by-Step: Sealing the Hole
1. Check the Pipe Pitch
Before sealing, confirm the pipes slope slightly downward toward the outside. This ensures any condensation or water that gets in drains outward rather than into your wall. If the pitch is wrong, talk to your heat pump installer before sealing.
2. Fit the Wall Sleeve
Slide a purpose-made pipe sleeve around the refrigerant pipes and drain hose. This fills the bulk of the hole and provides a clean surface to seal against. Some sleeves come in two halves for easy fitting around existing pipes.
3. Fill Any Remaining Gaps
If there are gaps larger than about 10 mm around the sleeve, press in foam backer rod first. This gives the sealant something to bond to and prevents it from sinking into a deep void.
4. Apply Exterior Sealant
Apply a continuous bead of exterior-grade flexible sealant around the sleeve on both the inside and outside of the wall. Smooth it with a wet finger or tool. On the exterior, make sure the sealant is fully bonded to the cladding surface — if you have fibre cement cladding like James Hardie products, ensure the surface is clean and primed if required by the sealant manufacturer.
5. Fit the Escutcheon Plates
Snap the decorative cover plates over the pipes on both sides of the wall. These hide the sealant work and give a tidy finish. Make sure the exterior plate doesn't trap water — it should sit flush or be sealed at the top edge.
6. Check the Interior Seal
Inside, the seal also helps with draught-proofing and thermal performance. A well-sealed penetration contributes to a warmer, drier home — important under the Healthy Homes Standards if you're a landlord.
Exterior Cladding Considerations
The approach may vary depending on your wall cladding:
| Cladding Type | Key Consideration |
|---|---|
| Weatherboard (timber) | Ensure sealant is paintable; prime bare timber before sealing |
| Fibre cement (e.g. Hardies) | Clean surface thoroughly; check if primer is needed |
| Brick or block | Use a mortar-compatible or masonry sealant |
| EIFS / plaster systems | Seek advice — these systems can be sensitive to incorrect sealing |
If your home has an EIFS (exterior insulation and finish system) or monolithic plaster cladding, it's worth getting a professional to check the penetration, as these systems have specific weatherproofing requirements under E2.
What You Cannot Do Yourself
While sealing the hole is DIY-friendly, other parts of a heat pump installation are legally restricted work in New Zealand:
- Electrical connections to the indoor and outdoor units must be carried out by a registered electrician. This is restricted electrical work under the Electrical Workers Registration Board (EWRB) rules.
- Refrigerant handling — connecting, disconnecting, or recharging refrigerant lines must be done by a certified refrigeration technician. Handling refrigerants without certification is illegal under NZ law.
Never attempt to modify the refrigerant lines or electrical wiring yourself.
When to Call a Professional
Call a qualified heat pump installer or builder if:
- The hole is oversized, irregular, or has caused visible damage to the wall framing or cladding
- You have a plaster or EIFS cladding system and are unsure of the correct method
- There are signs of existing moisture damage around the penetration
- The pipe pitch is incorrect and needs adjustment
- You're not confident working at height (e.g. on a two-storey home)
A qualified tradesperson can ensure the penetration meets the NZ Building Code's E2 requirements and give you peace of mind. You can find experienced local heat pump installers and builders on tradedirectory.co.nz.
ISO 9001
