Hot Water Heat Pumps - are they a rip off

By Eco Guy 5:14am 11th May 2010
We have a quick look at the cost benefits behind heating hot water using a heat pump...

There seems to be a lot of interest in using heat pumps (aka heat exchangers as found in air conditioning units) to replace traditional hot water heating methods (like an electric heater or gas). They are even being presented as possibly more efficient than a solar hot water heater...

The Cost of running a heat pump

Most heat pumps for the purposes of heating hot water seem to be rated around 1.3Kw - assuming a duty cycle of 33% (i.e. in operation for a third of time) and using a typical pricing model for water heaters of 11.3 cents per Kw. One gets a yearly electricity bill of around $285 attributed to the running cost of the heat pump alone. Now on the face of it this sounds great. But be aware the compressor is warranted for usually around 2 years max and the tank around 5years max. So if one assumes over 20 years that you could be up for replacing the compressor once every 4 years or so that's 5 compressors you would go through - not sure of the exact cost of this but lets put that at around $1500. The water tank should last maybe 10 years - so replaced once over 20 years - say another $1500.

So over 20 years - the heat pump would cost you in total (20 * 285 + 6 * 1500) = $14700. Add to that the installation cost and you get upto $18700.

Or look at this another way your current way of heating water would have to cost you more than $935 per year for a heat pump to be more cost effective.

So why the push for heat pumps?

I think this is simple really, they attract the same number of REC's as solar plus are easier to install and initially a cheaper outlay. But as we have shown over 20 years solar is more reliable and cheaper to run.

The Cost of running a solar water heater

The running cost of a solar water heater is usually in the circulation pump (if you have one). That's around 0.03Kw (30 watt) an hour. Assuming it runs half the time (dark at night) - that is an annual cost (on the same pricing model above) of $30. Now solar panels are usually warranted for 10 years (if you get a good one). So expect to be replacing that once in 20 years - circa $3000 I'd say. The circulation pump is around $300 tops and  would be replaced every 5 years tops. The hot water tank should last the same - so $1500 over 20 years.

Total cost over 20 years is 5000 + 30 x 20 + 3000 + 1500 + 300 x 4 = $6300

Or look at it another way your current way of heating your hot water would have to be cheaper than $535 per year to be more efficient.

Related Content Tags: heat pumps, solar water heating, water heating

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Comments left

  • Peter said:

    Hi Eco Guy,

    My father installed a Siddons Solar Plus Heat Pump 21 years ago. The system was well installed. At year 8 the service guy did a regular check over of the systems operations. No maintenance was required. In the last 13 years the system has not been touched. No work has been undertaken on our Solar Plus Heat Pump in 21 years.

    I don't know about other Heat Pump systems, but your theoretical calculations are not consistent with our 21 years of day-to-day experience with our Solar Plus Heat Pump.

    Regards, Peter

    ON Thu, 7 Oct 10, 12:25pm probably from Australia  Reply to this comment

    • Eco Guy said:

      Hi Peter,

      Interesting, I wasn't aware there was a hybrid system on the market; so you can get the best of both - do you have figures on the initial cost and the wattage rating/running times of the various electrical components - I'll then work out the break even point in yearly costs and update the article.

      As regards the other calculations - I'm going on the warranty periods now provided and the explicit exceptions often found; i.e. if a component is warranted for 20 years, its earliest point of cost to you failure would be in its 21st year.

      ON Fri, 8 Oct 10, 11:36pm probably from Australia  Reply to this comment

  • Stiebel Eltron said:

    You are telling the helpful information regarding hot water system that warm the water in sufficient way.

    ON Tue, 7 Jul 15, 10:41am probably from India  Reply to this comment

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