When is it time to replace your hot water service?

Aug 27, 2020

If your hot water service is between 10 and 14 years old you need to be thinking about replacing it and the first step is do your research. Here are some considerations if you are to replace your gas hot water service:

If you have solar panels (PV’s) on your roof say a 3kw system then you should consider installing a highly efficient heat pump as they consume 1kw of electrical energy to produce 3.5-4 kilowatts of heat energy. If you set the heat pump timer to operate during the day when your PV’s are producing electricity then it is very likely that you won’t be paying anything for your hot water.

Even if you don’t have PV’s on the roof you still should consider a high efficient heat pump because gas is not as cheap as it use to be and if you do your home work and do the maths and ignore the illusion created by marketing hype you might be surprised to find that a high efficient heat pump stacks up against natural gas. And here is one of the reason’s why. Heating water with electricity is 100% efficient so for every 1Kw of electricity you consume to heat hot water you get one unit of heat energy not so for gas the best condensing gas boilers can only get 94-96% efficiency so that means that for every 1Mj of energy you consume to heat hot water you only get 94-96% of one unit of heat energy. This means it will cost you 4-6% more to heat the same amount of water with gas compared to electricity. If you then go further and compare the heat pump to gas the heat pump is 350-400% efficient or a COP of 3.5-4.

If I looked at my own experience between 20/2/14 and 23/4/14(63days) I used 1861Mj. Our hot water needs are met by a gas boosted close coupled 300L Beasley solar unit. Apart from the solar gas boosted unit we have two other gas appliances one being a gas heater which wasn’t used during the said period and a cook top which we would use for 1/2hr on average a day. With all cook top burners operational the cook top would consume approx 40Mj/hr so if it operates for 1/2hr then it would consume 20Mj/day.

So 20Mj x 63days =1260Mj -1861Mj=601Mj. This value represents the Mj used by my gas boosted solar hot water service during the 63 days

I pay .019cents/Mj x 601Mj = $11.41. To convert Mj to Kw divide by 3.6. So 601Mj divide by 3.6 = 166.9Kw allow for a 400% efficiency or COP of 4 . So 166.9Kw divided by COP of 4 = 41.73Kw. I pay 26 cents/Kw. So .26/Kw x 41.73Kw = $10.85

Ok the savings are only 56cents but don’t forget this a period when the gas boosted solar is performing at it’s  best. If we consider the winter period when solar gain falls away dramatically the heat pump is not so much affected. It’s COP will only decrease to 3 to 3.5.

As I said before if I had PV’s my hot water wouldn’t be costing me anything. In fact if my hot water service was the only appliance on gas I would get the gas meter removed and save my self the service supply charge which was $37 for the same period or a saving of $215 for the year.

If you are replacing a gas storage with a gas instantaneous unit it is most likely that you will be faced with a gas line upgrade to cope with the demand for increased gas supply by the new gas instantaneous. In most cases you wouldn’t get make change from $1000 for the gas upgrade. Again, a high efficient heat pump should be considered.

Here are some considerations if you are to replace your electric hot water service.

Replacing your old electric hot water service with a high efficient heat pump should be one of your first consideration and not a solar boosted electric hot water service. Why I hear you say? Because the efficiency of a high efficient heat pump is equal to or greater than solar boosted electric. The Small scale Technology Certicficates (STC’s) values given to a hot water system is indicative of it’s efficiency performance for example a 315L squat tank Sanden heat pump gets 35 STC’s compared to a Rheem solar 270L loline with three Panels which gets 31 STC’s.

The other big issue is labour costs. A heat pump can be 1/3 of the cost to install and the reason is there isn’t any labour costs to install panels on the roof nor is there any labour costs to install insulated copper flow and return lines between the tank and solar panels.

Also don’t be afraid of heat pump technology your fridge uses the same technology and how long does your fridge last?