Your 1920s villa has character. High ceilings, original kauri trim, solid bones. But that original switchboard? It's probably not ready for what you're about to ask it to do. Adding a heat pump, HRV system, and extract fans to an older home often reveals a hard truth: the electrical infrastructure that served your grandparents' needs can't handle modern HVAC loads without upgrades. The electrical system and heating strategy must be planned together, not bolted on afterwards. This guide walks you through why older villas struggle with combined loads, how to assess what you actually need, and the practical steps to upgrade safely before your HVAC installer arrives.

Most character homes built before 1970 were designed for a single heating source and minimal electrical demand. Today's renovated villa needs to power multiple systems simultaneously: a heat pump drawing 2-4 kW, an HRV system using 45-100 watts continuously, extract fans, plus all your regular appliances. The maths doesn't work with original infrastructure.

Most older villas have a main supply of 10-15 kW total capacity

Your existing switchboard likely has one of three issues. First, it may be a fuse-based system (common in villas built before 1990), which is outdated and unsafe. Second, even if it has circuit breakers, the main switch capacity might be only 60-80 amps, when modern homes need 100-125 amps minimum. Third, there's simply no spare capacity.

A typical villa switchboard upgrade costs $1,500-$2,500 including labour and materials. That's not optional if you're adding serious electrical load. According to Cool Air's 2025 cost breakdown, electrical upgrades for heat pump installations range from $400-$1,200 for minor work, but full switchboard replacement runs higher.

A single heat pump might draw 2-4 kW during operation. An HRV system uses about 45-100 watts continuously. Extract fans add another 100-200 watts. If you're also planning a heat pump water heater (which draws 3-5 kW), you're looking at potential simultaneous loads of 8-10 kW or more.

Heat pump water heaters draw 3-5 kW during operation. Your heating, hot water, cooking, and laundry might all run at once during winter. The electrician's job is to ensure your switchboard can handle peak demand without tripping circuits or creating fire hazards.

When you upgrade insulation (adding ceiling batts, wall insulation, or double glazing), you reduce the heating load your heat pump needs to deliver. A well-insulated villa might need only a 5 kW heat pump instead of 8 kW. The NZBC H1 changes effective May 2023 increased insulation requirements for renovations. Better insulation means smaller HVAC systems, which means less electrical load.

Walk to your switchboard (usually in a garage, laundry, or under the house). Look at the main switch. It will show a number like 60A, 80A, 100A, or 125A. Multiply by 230 volts (NZ standard single-phase supply) to get kilowatts. So 100A × 230V = 23 kW theoretical capacity, but you should only use about 80% of that for continuous loads, giving you roughly 18 kW usable.

NZ electrical standards require 100-125A minimum capacity for modern homes (AS/NZS 3000:2018). Count your circuit breakers. Older villas might have 8-12 circuits. Modern homes need 20-30. If your switchboard is full, you're already at capacity. If you see fuses instead of breakers, the system is definitely outdated.

A 5 kW heat pump typically draws 2-3 kW during heating operation. An 8 kW unit draws 3-4 kW. HRV systems typically draw 45-100 watts continuously depending on fan speed. Extract fans add 100-200 watts each.

Here's a realistic example: A 1950s villa in Auckland with poor insulation needs an 8 kW heat pump (drawing 3.5 kW), an HRV system (80 watts), and two extract fans (150 watts total). That's 3.73 kW of new electrical load. If your current switchboard has 18 kW usable capacity and your existing appliances use about 8 kW during peak times, you're at 11.73 kW. You have headroom, but it's tight.

Once loads are calculated, the electrician will recommend one of three options:

Option A: New circuits only. If your switchboard has spare capacity and space for new breakers, you might just need new dedicated circuits for the heat pump and HRV. Cost: $400-$800.

Option B: Switchboard upgrade. Your existing switchboard is full or outdated, but the main supply capacity is adequate. Replace the switchboard with a modern unit with more circuits. Cost: $1,500-$2,500. This is common for villas with 1980s-1990s switchboards.

Option C: Full electrical upgrade. Your main supply is undersized (60A or less), or the entire system is dangerously outdated. This requires contacting your local lines company to upgrade the supply itself. Cost: $2,500-$5,000+.

The key to managing cost and disruption is staging the work properly. Don't install the heat pump first and then discover you need electrical work. Plan it backwards: electrical first, HVAC second.

Call a registered electrician and ask for a load assessment specifically for heat pump installation. A professional electrical load assessment costs $200-$400 and prevents costly surprises. The electrician will provide a written report recommending specific upgrades. This report is also useful for building consent if your renovation requires one.

If the assessment recommends a switchboard upgrade, schedule this before HVAC installation. The electrician will isolate the main supply (you'll be without power for 2-4 hours), remove the old switchboard, install a new modern switchboard with RCD protection (safety switches) and adequate circuits, then test everything and issue a Certificate of Compliance.

Switchboard upgrades include RCD protection and modern circuit breakers. This is a one-time investment that also improves safety and future-proofs your home for other upgrades (EV charger, solar, additional heat pumps). Older villas often have undersized cabling (2.5mm² when 4mm² is needed for heat pump circuits). New cabling ensures safe operation and prevents voltage drop.

Once the switchboard is upgraded, the electrician installs dedicated circuits for the heat pump (usually 20A circuit with 4mm² cable), HRV system (usually 10A circuit with 2.5mm² cable), and extract fans. Heat pump circuits typically require 20A breakers with 4mm² cable (AS/NZS 3000:2018). Cost: $400-$800 for new circuits and cabling.

Only after electrical work is complete and certified should your HVAC installer arrive. They'll connect the heat pump to the dedicated circuit, install the HRV unit and ducting, and commission the system. The electrician's Certificate of Compliance proves the electrical infrastructure is safe and ready.

The NZBC H1 changes (effective May 2023 for renovations) set higher insulation standards: ceiling insulation R3.2-R4.0, wall insulation R1.5-R2.2, floor insulation R1.3-R2.0, and windows with U-value ≤3.0 W/m²K (double glazing minimum).

Better insulation reduces heating load by 30-40% compared to uninsulated villas. A poorly insulated villa might need 8-10 kW of heat pump capacity. The same villa with H1-compliant insulation and double glazing might need only 5-6 kW. That's a significant reduction in electrical demand.

Suppose you're renovating a 1950s villa in Wellington. Current state: single glazing, no wall insulation, minimal ceiling insulation, heating load estimated at 9 kW. Your switchboard is 80A (18 kW usable capacity). Adding a 9 kW heat pump would consume half your available capacity.

Now upgrade to H1 standards: add 150mm ceiling insulation, retrofit double glazing, and seal draughts. The heating load drops to 6 kW. A 6 kW heat pump draws only 2.5 kW during operation. Your switchboard now has plenty of headroom. You might not even need a full switchboard upgrade, just new circuits.

Translation: better insulation reduces electrical load, which reduces upgrade costs. This is why planning insulation and electrical together makes financial sense.

The NZBC G4 clause requires fresh air ventilation. An HRV system meets this requirement while recovering heat from exhaust air. NZBC G4 requires minimum 0.35 air changes per hour for healthy indoor air quality. An HRV system uses 45-100 watts continuously. That's negligible compared to heating load. A 5 kW heat pump uses 2,000+ watts. The HRV is almost a rounding error electrically, but it's critical for health and compliance.

Installing a heat pump doesn't require building consent in most cases. However, the electrical work must be done by a registered electrician who certifies their own work (Certificate of Compliance). This is non-negotiable. Unregistered electrical work voids your insurance and creates safety hazards.

If your villa renovation includes structural changes, insulation upgrades, or rewiring as part of a larger project, you'll need building consent. Building consent fees for villa renovations typically range $500-$2,000 depending on scope. If you're doing a proper renovation that meets H1 standards, the electrical and HVAC upgrades are part of the consented work. The electrician's Certificate of Compliance becomes part of the final inspection.

You can stage work across multiple consents. Consent 1 covers insulation and glazing upgrades (H1 compliance), and Consent 2 covers electrical upgrade and HVAC installation (following insulation work). This approach lets you spread costs and manage disruption.

Your villa's character is worth preserving, but its electrical system isn't. If you're adding modern HVAC, plan the electrical upgrade first. Get a professional assessment, understand your current capacity, calculate your new loads, and stage the work properly: assessment → switchboard upgrade → new circuits → HVAC installation.

The investment is real. A switchboard upgrade costs $1,500-$2,500. New circuits add $400-$800. But this is a one-time cost that improves safety, enables future upgrades, and ensures your HVAC system runs reliably. Better insulation reduces the HVAC load needed, which can offset some electrical costs. And if you're doing a renovation that meets NZBC H1 standards, the electrical work is part of the consented project anyway.

Start with the electrician, not the heat pump installer. That single decision prevents costly rework and ensures your villa's modern systems are built on solid electrical foundations.