Pool heating retrofit in Pakenham - solar, heat pump or gas.
Three retrofit options on a Cardinia Shire family pool: solar evacuated-tube, electric heat pump, gas instant. Capex vs opex, the season-extension each delivers, the AusNet sub-circuit and the pool-cover ROI you can’t leave out of the maths.
The Pakenham heating-season problem.
A typical Pakenham family pool opens around mid-September and closes in late April. Without heating, water sits at 18-20°C either side of those dates and 22-28°C through the middle of summer. Heating extends both shoulders of the season - how far depends entirely on which technology you pick and whether you put a cover on top.
We’ve installed heating on roughly 40 retrofit pools across Pakenham, Officer, Beaconsfield, Cardinia Lakes and Heritage Springs. The economics are different enough between the three options that it’s worth working through them side by side rather than treating “pool heating” as one product.
Option 1 - Solar (evacuated-tube or roof-strip).
Solar piggybacks off the existing filter pump - a 3-way valve and controller divert water through roof-mounted collectors when collector temperature is above pool temperature, bypass when it isn’t. No gas, no extra electricity beyond the existing pump.
Capex on an 8×4 pool: $4,800-$7,200 installed. Roof-strip cheaper, evacuated-tube more expensive but ~30% more efficient per square metre.
Opex: effectively zero on top of normal pump running. The pump runs an extra 2-4 hours a day in shoulder season - maybe $50-$80 a year in electricity.
Season extension: 6-8 weeks. Opens late August, closes early May. Won’t heat through winter - there’s not enough sun on a Pakenham roof in July to do anything useful.
The catch: needs 50-60% of pool surface area in collector coverage on a north-facing roof. East-facing works at 70-80% efficiency, west-facing at 50-60%, south-facing isn’t worth installing. We’ll measure the roof first thing.
Option 2 - Heat pump (the Pakenham default).
Heat pumps move heat from outside air into the pool water using a refrigerant cycle. Coefficient of performance is typically 5-6 in mild weather - meaning every 1kW of electricity in delivers 5-6kW of heat into the pool. That’s why they win on running cost against everything except solar.
Capex on an 8×4 pool: $5,400-$8,500 installed for a 15-21kW unit, including dedicated AusNet sub-circuit, isolator and breaker. Inverter models are at the top of the range and worth the upgrade for the noise drop (under 50dB at 1m) and the part-load efficiency.
Opex: $400-$700 a year on a covered pool, $900-$1,400 on an uncovered one. Heat pumps struggle below 7°C ambient - on a 2°C Pakenham winter morning COP drops to 2-3, which is why we don’t recommend trying to hold 28°C through July.
Season extension: 14-18 weeks. Comfortable swim from late July through early June with a cover.
The catch: needs a clear 1m airflow zone around the unit (we’ll place it accordingly) and the dedicated circuit. AusNet upgrades are rare on Cardinia Lakes / Heritage Springs new-builds but occasionally required on older central Pakenham homes.
Option 3 - Gas (instant heat, expensive opex).
Gas heaters fire a flame across a heat exchanger - full pool temperature within 4-8 hours from a cold start. Brutal on running cost (no COP - it’s a direct fuel burn) but unbeatable for “heat the pool this weekend for the in-laws” use.
Capex: $4,200-$6,200 installed for a 200-250MJ unit, assuming an existing gas point at the equipment pad. Add $1,500-$2,800 for a new gas run from the meter if needed.
Opex: $40-$80 per heating day on a covered pool. Most gas-heated Pakenham pools we service are run weekends-only April-October - total season spend $500-$1,200 depending on use.
Season extension: effectively year-round on an “on demand” basis. Not the right tool for holding 28°C through July - that’s a heat-pump job - but the right tool for “Saturday is 32°C, heat the pool overnight, swim Sunday.”
The pool-cover line item you can’t skip.
60-80% of heat loss on an outdoor pool happens through surface evaporation. A bubble cover (a.k.a. solar blanket) cuts evaporation by 70%+ and effectively halves the energy bill on any heated pool.
Cover capex: $350-$700 for the cover itself, $600-$1,400 for a manual reel, $2,200-$4,800 for a powered roller. We recommend the reel for retrofits - powered rollers are for new-builds with the plumbing already in place.
ROI: 18-24 months on a heat-pump pool, faster on a gas pool. We won’t quote a heating retrofit without also quoting a cover - the numbers genuinely don’t work without one.
Quick questions before you decide.
Which option would you actually pick on your own pool?
Heat pump + cover, on a Pakenham 8×4. Best balance of season extension, running cost and reliability. Solar if we had perfect north-facing roof real estate, gas if we only wanted weekend bursts.
Can I run heat pump and solar together?
Yes - solar does the heavy lifting in shoulder season, heat pump tops up early and late, neither runs hard. Capex is high (both systems installed) but opex collapses. We install this combination occasionally on entertainer pools in Lakeside.
Will pool heating mess with the chemistry?
Slightly. Warmer water grows algae faster, so heated pools run weekly servicing year-round (versus fortnightly for unheated). Chlorine demand goes up roughly 20-30% on a heated pool. We adjust the chlorinator output accordingly.
How long does the install take?
Solar: 1-2 days. Heat pump: 1 day plus electrician visit. Gas: 1 day plus gas-fitter and (if new run) trench day. Pool stays swimmable through the whole install.
Want a heating quote on your Pakenham pool?
We measure, look at the roof / equipment pad / switchboard, and quote all three options side-by-side - including cover. No upsell to the most expensive option.