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Heat Pump vs Gas Heater Cost to Heat a Pool

Posted by Dr Gregory Grochola (physicist) on 6th Mar 2019

In this article we analyze the savings from using a pool heat pump vs a gas heater to heat your pool. The results are somewhat surprising as they are highly dependent on the Australian state in question. There have been some pundits with opinions on the subject, but let's look at what the actual science says, as the heating loading calculations are complex.

BTW all these our calculations were performed using our new pool heating costs calculator (validated against the heat loading standards AS 3634-1989 and ISO TR 12596 1995 here).

pool-heat-pump

So to study the subject we calculated the heat loadings on a standard pool, heated to a temperature of 29°C for most state capitals, 31°C for Brisbane and 33°C for Darwin. We looked at both, year-round heating and a standard pool heating season length (defined below). We then used the heat loadings to calculate the heating costs for a heat pump and gas heater to find the relative cost savings from using a heat pump.

We should also mention we actually looked at other variations, such as wind exposure, dark pool walls, and blanket use but nothing really changed the ratios much, except for season length which changed them a little as we'll see below. This makes sense as the savings will primarily depend on the gas and electricity costs and secondly the temperature and humidity at which the heat pump is run.

The capitals we looked at were, Hobart, Melbourne, Canberra, Sydney, Perth, Adelaide, Brisbane and Darwin. But before we get into the costings lets define the heating season length.

Calculation Definitions and Data Used

Heating Season Length

We calculated two extreme swimming season lengths - some people heat their pools all year while others are more conservative and may only run their heaters during a standard swimming season (or less). Knowing this range allows you to get a good sense of the savings if you choose to run your heating somewhere in between these two limits.

Year-round heating means we ran the heater year-round of course, while a standard solar heating season was defined as what you'd get from a well sized solar pool heating system:

Standard Solar Season Heating Month Definitions

Month
Hobart
Melbourne
Canberra
Sydney
Perth
Adelaide
Brisbane
Darwin
Jan
Heat*
Heat*
Heat*
Heat*
Heat*
Heat*
Heat*
Heat*
Feb
Heat
Heat*
Heat*
Heat*
Heat*
Heat*
Heat*
Heat*
Mar
Heat
Heat
Heat
Heat
Heat
Heat
Heat*
Heat*
Apr
...
...
Heat
Heat
Heat
Heat
Heat
Heat*
May
...
...
...
...
...
...
Heat
Heat
Jun
...
...
...
...
...
...
...
Heat
Jul
...
...
...
...
...
...
...
Heat
Aug
...
...
...
...
...
...
...
Heat
Sep
...
...
...
...
...
...
...
Heat*
Oct
...
...
...
...
...
...
Heat
Heat*
Nov
...
...
Heat
Heat
Heat
Heat
Heat*
Heat*
Dec
Heat
Heat
Heat
Heat
Heat
Heat*
Heat*
Heat*

* if required

How We Defined "Heating Costs Savings"

In the tables that follow, "Heating Costs Savings" are defined as - 1st year energy cost ONLY. These are saving in running costs ONLY - they do not include heater unit replacement or maintenance cost.

Energy Costs

Energy costs used in the calculations in each state are shown also as they can vary quite substantially. They are state average, but if you have different rates you'll need to adjust the ratio savings. These rates are sourced from: "Gas Price Trends Review 2017", Version 2.1 March 2018, source: https://www.energy.gov.au/publications/gas-price-trends-review-report. And for electricity rates are sourced from: https://reneweconomy.com.au/market-insight-residential-electricity-price-series-96026/.



Pool Heat Pump Vs Gas Heater

Heating Cost Savings

State Capital
Gas Cost (c/MJ)
Tariff Cost ($/KWH)
year-round heating
Standard Season
Hobart
3.9
0.33
51%
55%
Melbourne
2.3
0.34
16%
23%
Canberra
3.0
0.28
43%
49%
Sydney
3.4
0.38
41%
46%
Perth
4.1
0.33
57%
60%
Adelaide
4.5
0.48
41%
45%
Brisbane
6.4
0.35
71%
72%
Darwin
4.5
0.29
69%
69%

Findings Summary

So clearly if you had a choice between a running a heat pump or a gas heater, just based purely on running costs, heat pumps are a clear winner in almost all states. Brisbane and Darwin offer heat pump running cost savings of a whopping 70% compared to gas heaters. Less than 1/3rd the cost to run. These are both high temperature, high humidity states which help heat pump efficiencies. They also have relatively low electricity rates and gas energy costs. Most other states show 40% to 50% savings, while chilly Melbourne with it's low gas costs show only 16% savings. In fact in Melbourne if you run an efficient gas heater and a not so efficient heat pump, the gas heater may actually be cheaper to run, pretty much the only situation in Australia where a gas heater will be cheaper.

Limiting the heating season to just the standard length boosts savings a little because the heat pump is only run in favorable warm conditions, while gas heater efficiencies are insensitive to air temperatures.

If you have a specific set of heat loadings on your pool, try our online pool heating running cost calculator. Auxiliary heaters can get expensive fast without solar covers or other smart measures, so it's well worth spending some time playing around with the calculator trying different settings.

If you enjoy this article please share, link and drop a comment on Disqus :)



Just for Fun - Academic Exercise

What follows is more an academic exercise if you're interested. As we were curious what savings we could get over gas heaters if we maxed out all tricks, i.e. added a solar blanket to the heat pump, and then only used the pool only during warmer pool swimming seasons times. The following is not fair on gas heaters of course as we're comparing heat pumps run WITH energy saving measures - to gas heaters run all year WITHOUT energy saving measures... so keep that in mind.


Pool Heat Pump + Pool Blanket (87.5% usage)

vs

Gas Heater

Heating Cost Savings

State Capital
Gas Cost (c/MJ)
Tariff Cost ($/KWH)
year-round heating
Standard Season
Hobart
3.9
0.33
76%
83%
Melbourne
2.3
0.34
62%
80%
Canberra
3.0
0.28
74%
87%
Sydney
3.4
0.38
76%
87%
Perth
4.1
0.33
84%
93%
Adelaide
4.5
0.48
77%
88%
Brisbane
6.4
0.35
89%
93%
Darwin
4.5
0.29
96%
96%

So adding a solar blanket to the above heat pump scenario yielded significant savings as expected. Running a heat pump with a blanket (at 87.5% usage) for a standard pool season cut pool heating cost at a minimum to 80%, or 1/5th that of a gas heater. Now let's do one more comparison because we arrive at a striking result.


Pool Heat Pump + Pool Blanket + Standard Season Length

vs

Gas Heater Heating + No Blanket + All Year-round

Heating Cost Savings

 (Responsible Vs Irresponsible Pool Heating)

State Capital
Savings
Hobart
95.5%
Melbourne
96.4%
Canberra
95.8%
Sydney
97.7%
Perth
95.8%
Adelaide
94.6%
Brisbane
95.9%
Darwin
95.8%

So for this comparison we're really running a gas heater irresponsibly; all year-round without a blanket and comparing this to running a heat pump with a blanket and only using the pool during a standard solar season. Not surprisingly, the costs fall to a small fraction: about 1/20th that of the gas heater.

What's surprising is that the saving between states levels out dramatically. The main reasons for this, is the fact that year-round vs standard solar season savings are loop sided toward cooler areas, hence if we looked at the saving from using the pool for a standard season vs year-round we'd get...


Year-round Heating

vs

Standard Season Pool Use

Heating Cost Saving


State Capital
Savings
Hobart
75%
Melbourne
73%
Canberra
68%
Sydney
67%
Perth
65%
Adelaide
65%
Brisbane
49%
Darwin
0%

In other words, in Hobart if we used the pool for the standard season we'd be paying just 25% or 1/4th the cost of year-round heating. This explains the surprising result above where all the savings leveled out somewhat... Anyway, we thought this result was an interesting one.. but purely of academic value perhaps :)