How do continuous flow water heaters work?

When a hot water appliance is heated by a constant flow water heater, the cold water passes through the water heater and a flow sensor linked to the ignition switch will activate the heating of the water instantly. (There is no stored hot water in the appliance at all meaning no extra storage cost, and instant heated hot water).

The flame size and heating will then be controlled by solenoid valves and sensors all of which connect to a circuit board and essentially a minicomputer inside the appliance. 

This computer will communicate with all the various sensors throughout the appliance to either create an action in the appliance or receive information back in the form of an error code shown on a red digital screen which varies between appliance brands. 

Continuous flow water heaters (also known as instantaneous water heaters) are designed to deliver hot water for the entire duration at which the hot water is being used. The only factors that may stop this appliance from operating under normal conditions is

  • if the water supply runs out (tank water this is possible)
  • if the gas supply runs out (if on LPG bottles this is possible when bottles empty, if on natural gas this is possible if there is a fault or outstanding bill)
  • if there is a power cut or outage or fault with electricity – or if appliance power has been switched off at plug or unplugged. (Some Specialised continuous flow water heaters operate without the need of power, instead using their own mechanical power generators for spark ignition). 

What common brands of constant flow Water heaters are there?

The most common brands accessible straight off the shelf in most plumbing merchants are Rheem and Rinnai. Rheem constant flow water heaters often called Rheem Integrity for most domestic size constant flow heaters. Rinnai constant flow water heaters are often called Rinnai Infinity.

Both above-mentioned hot water systems are normally comparable and the quality is similar between these brands.

There are other brands in the New Zealand market that may be worth looking at, some may have different qualities to the others. 

The cost of installation is going to vary between each house and depend on distance of gas pipe and water pipes run, accessibility, and location. This will be different for every house. 

How big are continuous flow water heaters?

The size depends on the volume heater you install. Each heater is specified to a Litres per minute rating indicating how much hot water they can deliver per minute. Most average size houses with continuous flow water heaters in NZ will have 18L to 22L Heaters. They are most often mounted on an exterior wall with adequate clearances to openings and other hazards or obstructions (This is required by Law and important when considering installation locations).

They normally come in the form of a white box no more than 0.5 metres wide and 800 high for average houses. And stand less than 0.3 metres off the wall. So generally they are quite compact appliances that can often blend seamlessly to the exterior wall.

Operating and Maintenance Tips

There is not much maintenance required on these appliances for the homeowner. It is important to keep clear the appliances exhaust vent so some tree trimming may be necessary.

It’s also a good idea to clean and wipe appliances occasionally to keep the outside casing in good condition. Each continuous water heater will have a flow filter at the bottom that should be checked at least every 6 months (this depends on water quality). Most homeowners will get the plumbers out to do this however it can be done by the homeowner if they are careful and know where to access the filter, it is not a very difficult process.

Clearing these filters will ensure the continuous flow water heaters continue to operate correctly and cause no errors. If the filters block up too much, it will be sensed by the appliance and likely cease to function as an error code is present, until fixed. 

Installation Requirements

There are a number of clearance and ventilation requirements for continuous flow water heaters, mainly outlined around providing adequate ventilation of the appliance without creating any kind of situation where buildup of the fuel products or products of combustion can create a potentially hazardous environment.

Possible factors requiring clearances could be windows or other openings, drain openings, overhangs, corners etc. This means that there are several installation clearances that need to be adhered to make the installation legally compliant.

The manufacturers of the appliance will have their installation requirements and then the other installation requirements can be accessed from the current New Zealand Gas Code for the continuous gas flow water heaters. These water heaters should only be installed by gasfitters to ensure compliance.

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