From Gas to Solar: Should You Go Traditional Cylinder or Heat Pump for Your Hot Water?

If you're still on gas for hot water, you're in a pretty common spot. But now you’re weighing your switch options — traditional electric cylinder with solar vs a shiny new heat pump cylinder. Which one actually makes sense in the long run?


Here’s the brutal, no-fluff breakdown — from someone who’s thought about this way too much.


The short summary is; most homes don't have the perfect roof for winter solar production. So; most homes should get a heat pump hot water cylinder. But for those who have a stunning north facing roof, a traditional cylinder + an extra 6 - 10 more panels is the way to go.


🔍 What EECA Actually Says About Heat Pump Cylinders


  • Heat pump water heaters use a vapour-compression cycle to pull heat from the air and transfer it to your water. It’s clever. EECA
  • According to EECA, they typically use 60–75% less electricity than a standard electric cylinder — and are cheaper to run than gas over time. EECA
  • But: they come with a higher upfront cost, and their lifespan is shorter — generally between 8 and 15 years, because of all the extra mechanical parts. EECA
  • They can also be a bit less efficient in colder outdoor air — when it’s freezing, that heat pump has to work harder. EECA


💡 Why Traditional + Solar Is Often the Smarter Long-Term Play (Especially for Solar-Optimised Homes)


If you’ve got a north-facing roof at a good pitch (20° or more), here’s where the math gets fun:

  1. Add more panels, not a heat pump.
    Tacking 10 more panels equate to another 4.5 - 5kW of solar panels. Adding them onto your typical 12 panel quote costs roughly the difference between a traditional and a heat pump cylinder. ($6,000 ish).
    Those 10 panels will produce the 3kW your cylinder needs on most days, even with a little cloud. And on a dark day, they'll still generate enough to power about half of the traditional cylinders energy demand.

  2. Longevity is on your side
    Traditional cylinders + well-installed solar systems can easily last 25–30 years. Heat pump cylinders? Likely need replacement after 12–15 years. That means another big bill down the line.
  3. Lower maintenance risk
    Fewer moving parts, fewer failure points. On the contrary, Heat Pump Cylinders need maintenance every few years to ensure their warranty is honoured. The sacrificial anode must be replaced every 4–  5 years to extend the cylinder’s life — but unless you’re a licensed plumber,
    you legally can't do it yourself.  So the ‘cheap maintenance’ argument for heat pump cylinders often forgets the bit where you’re calling a plumber anyway.
  4. Better alignment with solar
    With solar powering a traditional cylinder, you’re storing your sunshine in hot water. Over time, that’s gold. Whereas a heat pump draws consistent power and is less able to flex with variable solar generation.


⚠️ When a Heat Pump Could Be The Smart Choice


  • You use a LOT of hot water — big family, long showers, high demand. The efficiency gains from a heat pump start to make real sense.
  • You've got a small roof - because if you can't fit the extra panels, get the heat pump cylinder!
  • Your roof is under 20 degrees, and / or isn't facing mostly north - because anything but 20+ degrees north performs poorly in winter, which means high winter bills. Better to go with a heat pump cylinder and have guaranteed & low cost water heating.
  • You don’t mind replacing gear — if you're okay with swapping out the unit in 10-ish years, the savings during its life could justify it.
  • Space + noise work for you — because of the fan & compressor, your heat pump will need to live outside or somewhere it won’t annoy the neighbours. EECA


🔭 The Long-Term Betting Strategy (From Your Friendly Solar Broker)


Here’s our take (and yes — there’s a strategy):

  • If your roof is solar-friendly (north-facing, decent pitch), lean into traditional cylinder + solar. Use your panels to power that cylinder, and let it run happily for decades.
  • Don’t be tempted to spend on a heat pump unless you’ve run the numbers with all-in costs (buy, install, maintain, replace).
  • If you go heat pump, make sure someone has correctly sized it to match how much hot water you actually use. Too big or too small, and the maths breaks.
  • Remember: your solar system is one of your best long-term bets. It’s not flashy, but it’s steady, reliable, and built to last.


🍟 Some options to consider - just an indication


Consider these:

  • 12 panels installed + a good quality heat pump hot water system: $21,000
    *The heat pump cylinder will likely need replacing around year 15, and it will need maintenance every 5 years.

  • 22 panels installed + a traditional heat pump cylinder: $21,000
    *Both the panels and the cylinder are likely to last 30 years.


Same price. Similar outcome on your power bills, but a very different story once you factor in replacement and maintenance costs.


✅ Final Verdict


For most former-gas households with good solar potential, adding panels + a traditional hot water cylinder is going to pay off bigger, longer, and with less headache than jumping into a heat pump setup + a smaller solar system.


Some solar companies don't like our position on this. But just think for yourself, and ask, how many old homes in NZ are still running traditional hot water cylinders from the 90s?


Heat pumps are sexy, efficient, and “green.” But if you want long-term stability, fewer moving parts, and a system that just works — the old-school storage cylinder, powered by sunshine, (and a few more solar panels), often wins.


PS: Already got a traditional cylinder? Read our blog about your smart solar & hot water options.

By looka_production_130270016 December 29, 2025
Because the numbers don't lie
By looka_production_130270016 December 28, 2025
Cheap solar isn’t cheap because the gear is bad — it’s cheap because responsibility quietly shifts to the homeowner.
By looka_production_130270016 December 23, 2025
Solar panels are so cheap now that even selling excess energy back to the grid at so-called “peanut” rates can still be a very good investment. So let’s talk about solar the right way — not emotionally, not politically, and not based on what your neighbour reckons. Most people say, “Selling solar to the grid isn’t worth it. It’s peanuts.” And our response is always the same: “Nothing wrong with peanuts” Reality is, solar should be considered in the same way all investments are considered. The question is - What am I spending, and what am I getting ? The Abraham Argument (sorry, its a bit of fun) In the book of Genesis, Abraham argues with God over the prospect of saving Sodom and Gomorrah from a terrible punishment. Moses asked god - “Would you save the city for 50 righteous people?” “How about 40?” “30?” “Come on… 20?” “Wait — before you send the fire — how about 10?” That same bargaining logic works beautifully with solar. Let’s assume the absolute worst-case scenario and argue backwards. Check Out Abrahams Sales-Pitch Imagine this: 18 solar panels Cost: $5,000 (totally unreasonable) Annual generation: ~10,000 kWh Every single unit sold to the grid Buyback rate: 17c per kWh Those panels would pay you $1,700 per year in solar buyback credits. No self-consumption. No batteries. No optimisation. Just exports. That’s under a 3-year payback . What do you reckon? Would you do it? Moses - “I’ve got my hands on the stone tablets. And I’m telling you – you can’t get 18 panels for $5,000. But let me ask you…” How Many Donkeys Would You Trade For 18 Panels? If exports alone deliver $1,700 per year in export credits, would you buy 18 panels if they cost: $12,000? (5.9-year payback) $14,000? (8.2-year payback) How about $16,000 and some unleavened bread? (9.4-year payback) ... $16,000 is about what 18 panels cost for most homes. You can forget the unleavened bread. And by the way, Abraham forgot to tell you 👉 $1,700 is the worst this system could save you. Why You'll Save More Than Moses Reckons If you sell solar to the grid, Moses already told you its worth about 17c per kWh (give or take). But the solar you actually use is worth more! It’s worth your retail rate — typically 30–40c per kWh incl GST. That changes everything. Also, If your roof is a decent north-facer with more than a 10° pitch, 18 panels won’t generate 10,000 kWh. They’ll generate more . Good roofs regularly see 11,000 kWh with 18 panels (460w assumed). Great roofs can push 12,000+ kWh per year! Tearing Down The Strawman Argument In the real world: 18 panels typically save ~$2,000 per year without a battery Add a battery and that can push closer to $3,000 per year (book a consult with us to iron out the finer details). So, if Abraham were here, he wouldn’t be arguing about buyback rates. He’d be covering the city in panels to power his DC grain mills and DeWALT power tools. (That's how they built the temple so quick. DeWALT all day)! Because if you can spend $16,000 today and save $2,000 per year minimum , you’re looking at roughly a 7–8 year payback . Over 25 years? That’s $50,000+ in savings when you bake in 3% inflation . Closer to $70,000 if you don't subtract the cost of adding a battery in 5-10 years. But we think the battery will be necessary, because the buyback rates will eventually trend downwards - and you can't expect $70,000 in savings without adding a battery when they become a necessity. The Takeaway Solar exports aren’t the dream scenario. They’re the floor . And when the floor already looks this good… the upside takes care of itself. Disclaimer: You may not be able to sell all of what 18 panels can generate. There are limitations. However - those limitations become entirely irrelevent if your home pulls ~2.5kW of energy during the peak hours between 10 & 2. It's not all that hard to get your home doing this. Pool Pump, Spa, Hot Water Cylinder, Aircon in summer + Fridge and Freezer all add up to a hell of a lot more than a 2.5kW energy demand. And so; the export limit is mostly irrelevant on homes with 18 panels or less. Once you have more than 18 panels, the story changes - but the story is also developing, because more and more networks are unlocking 10kW buyback on one phase, instead of the standard 5kW buyback per phase. And of course, if you have multiple phases (2 or 3) you can get away with 25 - 35 panels and experience zero limits to how much you export.