We have been heating water for centuries with everything from wood fires to the sun.
This is not an all-encompassing doc on all available water heaters or heating water — more about the trend towards Heat Pumps. There is a smaller trend to high efficiency in continuous flow water heaters. And there is a trend away from gas to electric. People with tight budgets are more inclined to go for cheap install costs and not the long-term cost of hot water.
Your situation might dictate a solution
Or you are selling the property and the cheapest water heater will do. In which case a straight swap or repair of the current one might be your choice.
Climate Change
Climate change whether you believe it or not, is causing those who do think it is a thing to consider heating water with heat pumps or going electric. Gas is less favourable than it was. At least from ground-sourced gas. Biogas is on the up. The products used in biogas production would have generated methane anyway.
If lots of people shift to electric all at once, additional power generation will be needed but this can be mitigated by having your electric storage tank heated at night. Some suppliers have a cheaper night rate. If we do not change how we supply electricity or manage it most countries will fire up coal boilers making the outcome a lost cause for the environment as coal puts a lot more CO2 into the atmosphere than Natural Gas which is mostly methane.
Is Biogas a thing?
Just for the record, most countries have biogas going to waste often at landfills, food processing plants, or sewage treatment plants. So that is methane going into the atmosphere that could be used for heating or power generation resulting in much better CO2 going into the atmosphere rather than Methane. Plus you get the benefit of the heat.
Is electricity really 100% clean?
But if we must use electricity then putting the power into a heat pump is the more efficient way as it uses about a third of the power than an immersion element. The heat pump uses heat from the atmosphere to heat the water.
It has a similar return to solar hot water heating.
Most countries have a percentage of power that is renewable the rest comes from coal/gas or woodchips. In New Zealand it is around renewable is 90%.
Types of Heat Pump Water Heater
Generally, two types:
- Connected water heaters
- Split water heaters
This is where the compressor is mounted on top of the water heater or installed in a different location.
The connected models are a lot cheaper to buy and install but not as powerful as the split models. If you have serious water heating then you will need a split model and the power supply to go with it.
The split models are fine for residential use and there are a variety of capacities. They usually start around 180-190 litres up to 325 litres. The capacity to heat is the size of the compressor and its Coefficient of performance. Some tanks only heat part of the tank. They all usually have an immersion element for when demand is higher than the heat pump needs a boost.
In all the tanks I have installed I have the element turned off and there has not been any need for an element. If you are using the element what is the point of the heat pump aspect.
Cleansing Functions
Heat pumps during winter are fighting low temperatures, and it is possible in very cold climates for the heat pump to struggle to heat water to 60ºC. The reason the heat pump wants to go to 60ºC is because there is a bug called Legionnaires bacteria which is killed when water is at 60ºC. Most water heaters have a system that overrides temp settings to get to 60ºC once a week. This is often hard-coded into the water heater controls. This can cause noise issues if the water heater is placed near bedrooms which you should avoid.
Locations
Outside is the most common and near kitchens if possible. Inside is possible for some of the quiet models and if you can take warm air from ceiling spaces or channel it to the water heater even better. The warmer the air the more efficient. Ensure airflow at the compressor is not restricted and some water heaters spec a distance off the wall.
Location can be a big issue for heat pumps both water heating and space heating. There are some city locations where there is no land to put them requiring brackets on the sides of buildings making servicing a problem. You cannot have them hanging over boundaries or near neighbours’ bedrooms.
If theft could be a problem you will have to cage them to make it more difficult to take them. They start in price from $3,500 to $9000 for the combined units so quite attractive to take. Split systems even more. There could be clashes with other things such as space heating heat pumps too and their discharge.
How much extra do they cost?
The immersion water heater is the cheapest replacement and is similar to a gas continuous flow water to replace in the same location. The running cost is the lowest for the gas water heater.
It is always a running cost vs capital cost battle. The more expensive water heaters have low running costs. Cheap storage tanks or continuous water heaters have low capital costs but high running costs compared to heat pumps or solar water heaters, and it depends on the quantity of hot water needed. Large quantities of hot water are cheaper to produce per litre.
People with very high use e.g. a hairdresser or large restaurant will need big storage or gas continuous flow water heaters.