If your hot water system isn’t keeping up, the first thing most people blame is the unit itself.
They assume it’s faulty, underperforming, or just a “bad system”.
But in a lot of cases, especially with a heat pump hot water system in North Lakes, the real issue is much simpler:
It was never sized properly for the household.
Why Sizing Is the Hidden Problem
We’re seeing more and more heat pump hot water systems installed across North Lakes and the wider Moreton Bay region, and one of the most common issues we come across is mismatch.
The system might be working exactly as designed…
…but it’s not designed for how the household actually uses hot water.
When that happens, you end up with:
- Running out of hot water at the worst times
- Systems constantly reheating
- Higher-than-expected electricity bills
- Units working harder and wearing out faster
And from the outside, it just looks like “the system isn’t very good”.
Heat Pumps Work Differently (And That Changes Everything)
A lot of people don’t realise this:
Heat pump hot water systems don’t recover as quickly as gas systems.
They’re more efficient, but slower to reheat.
That means sizing isn’t just important…
it’s critical.
If you undersize a heat pump:
- It won’t keep up during peak demand
- It will run more often to try and catch up
- It may switch to less efficient modes depending on the system
So while you might save energy in theory, in reality you end up paying more.
It’s Not Just “How Much” Hot Water; It’s “When”
Most sizing guides focus on total daily usage.
But in real households, timing matters more than totals.
For example:
- A couple who use hot water across the day → low peak demand
- A family of four showering back-to-back at night → high peak demand
Those two households could use the same amount of water daily…
…but require completely different system sizing.
This is where a lot of installs go wrong in North Lakes homes, especially in newer builds.
Common Signs Your System Is Undersized
If you’re not sure whether your heat pump hot water system is sized correctly, look for these signs:
- You run out of hot water during back-to-back showers
- The system seems to be running constantly
- Your power bill is higher than expected
- You have to “manage” hot water usage in your own home
- The unit struggles more during colder weather
These aren’t always faults.
They’re often symptoms of a system that’s too small for the job.
Solar, Tariffs and Timing Make It Even More Important
A lot of homes in North Lakes are now running:
- Solar power
- Controlled load tariffs
- Off-peak electricity
That changes how your system should be sized.
If your heat pump is set to run during the day (to take advantage of solar), it needs enough storage to carry you through peak evening demand.
If it doesn’t:
- It will kick in at night on peak rates
- Or you’ll run out of hot water altogether
So now sizing isn’t just about capacity…
It’s about strategy.
Where Most Installations Go Wrong
What we’re seeing across Moreton Bay and North Lakes is:
- Systems selected based on price, not usage
- “Standard” sizes installed regardless of household
- No consideration of peak demand
- No planning around solar or tariffs
- Installers treating heat pumps like electric tanks
That’s how you end up with a system that technically works…
but doesn’t actually work for you.
How We Approach Heat Pump Sizing at RJT
At RJT Plumbing and Gas, we don’t just look at the spec sheet.
We look at how your household actually operates:
- Number of people in the home
- Shower habits and timing
- Simultaneous usage (laundry, kitchen, bathrooms)
- Energy setup (solar, tariffs, peak/off-peak)
Then we match the system to that.
Because the goal isn’t just:
“Install a heat pump”
It’s: Make sure you never think about your hot water again.
Planning an Upgrade or Not Sure About Your Current System?
If you’re in North Lakes or the Moreton Bay area and your system isn’t keeping up, or you’re looking at upgrading to a heat pump, getting the sizing right upfront will save you a lot of headaches later.
We can help you figure out:
- Whether your current system is undersized
- What size actually suits your household
- Whether your setup is working against you
