Instant gas water heaters

Instant gas water heaters, also known as gas instantaneous water heaters, gas on demand water heater or an instant gas water geyser, provide instantaneous domestic hot water to your hot water outlets on demand. They are also known as on demand water heaters or tankless water heaters.

They are instantaneous gas water heaters that are both an energy efficient (instantaneous water heaters have no standby energy losses) and cost effective way to produce a reliable and consistent supply of hot water for a shower, bath, and other hot water taps in your property or building.

These energy efficient instant hot water heaters can be used in domestic (houses and apartments) or commercial applications and provide endless hot water as long as you have access to an adequate gas supply (natural gas or LPG propane gas type) and mains water supply flow rate.

Gas instant water heater systems can reduce gas usage by up to 30% compared to traditional storage tank water heaters, as instantaneous water heaters have no standby energy losses and only heat hot water on demand resulting in energy savings.

There are two simple rules that govern instant water heating

The power output of the instant on gas water heater directly relates to the temperature rise of the water that can be achieved when producing hot water on demand.

This temperature rise affects the flow rate the instant water gas heater can produce.

It’s just laws of physics at work with instantaneous gas water heaters, be they natural gas or propane powered gas type.

Gas instantaneous water heater product range

Our gas tankless water range consists of the following energy efficient and cost effective units 

SF14 – 24kW Low NOx gas tankless water heaters

This 24kW gas instantaneous water heater designated the SF14 model. This is a low NOx gas water heater and is available in natural gas or propane.This instantaneous water heater has a large 16mm water ways copper heat exchanger, for lower risks of clogging, very low pressure drops and high efficiency. They have a 35°C to 60°C heating water temperature control and are fitted with a safety cut out high temperature thermostat.

This unit can only be used in a domestic house or flats and can’t be used in commercial hot water system applications.

Water heating performance for the SF14 domestic gas instantaneous water heater is –

The full manual for this model can be downloaded here which has the technical data, dimensions etc  

Download the SF14 Low NOx gas fired instantaneous water heater manual – Flexiheat UK

There are two options for the 28kW and 34kW instantaneous water heaters units, which are

“SFC” types are used for direct on-demand water heating systems without DHW recirculation because they lack an internal pump.

or

The  “SKF” versions with an internal pump for DHW return systems are frequently used in larger water heating applications.

28kW instantaneous water heaters

SFC /SFK 28 Gas fired instantaneous water heaters – Condensing -Tankless,with stainless steel heat exchanger

Water Temperature Rise	Δt 20	Δt 25	Δt 30	Δt 35	Δt 40	Δt 50	Δt 60	Flow rate
SFC / SFK 28	20.66	16.53	13.78	11.81	10.33	8.27	6.89	Litres/min
	1239.89	991.91	826.59	708.51	619.94	495.96	413.3	Litres/hour

 

Download the SFC28 Gas water heater manual with no pump – Internal version

Download the SFK28 Gas water heater manual with pump – Internal version

34kW instantaneous water heaters

SFC /SFK 34 Gas fired instantaneous water heaters – Condensing -Tankless,with stainless steel heat exchanger

Water Temperature Rise	Δt 20	Δt 25	Δt 30	Δt 35	Δt 40	Δt 50	Δt 60	Flow rate
SFC / SFK34	25.09	20.07	16.73	14.34	12.55	10.04	8.36	Litres/min
	1505.4	1204.46	1003.72	860.33	752.79	602.23	501.6	Litres/hour

Download the SFC34 Gas water heater manual with no pump – Internal version

Download the SFK34 Gas water heater manual with pump – Internal version

50kW instantaneous water heaters

SFK50 Gas fired instantaneous water heaters- Condensing – Tankless

NB: This unit is only available with a pump, which can be switched on or off depending on your water heating system requirements, i.e., straight through on demand water heating or a DHW recirculation water heating system.

Water Temperature Rise	Δt 20	Δt 25	Δt 30	Δt 35	Δt 40	Δt 50	Δt 60	Δt 75	Flow rate
SFK50	36.90	29.52	24.60	21.09	18.45	14.76	12.30	9.84	Litres/min
	2,214	1,771	1,476	1,265	1,107	886	738	590	Litres/hour

Download the SFK50 Gas water heater manual with pump – Internal version

Larger gas fired instant hot water heater range

For larger hot water on demand water usage requirements, we do a commercial and industrial gas instantaneous water heater range, these are detailed further on this dedicated webpage, commercial instantaneous water heaters, which are available in 150kW or 200kW outputs, but here briefly is the hot water performance of the units.

Our 150kW model

Water Temperature Rise	Δt 20	Δt 25	Δt 30	Δt 35	Δt 40	Δt 50	Δt 60	Δt 75	Flow rate
SFKG 150	110.19	88.15	73.46	62.96	55.09	44.08	36.73	29.38	Litres/minute
	6,611	5,289	4,408	3,778	3,306	2,645	2,204	1,763	Litres/hour

and our 200kW model 

Water Temperature Rise	Δt 20	Δt 25	Δt 30	Δt 35	Δt 40	Δt 50	Δt 60	Δt 75	Flow rate
SFKG 200	146.92	117.53	97.94	83.95	73.46	58.77	48.97	39.18	Litres/minute
	8,815	7,052	5,877	5,037	4,408	3,526	2,938	2,351	Litres/hour

 

To select the correct instantaneous water heaters for your needs, please read on

Showers and other domestic hot water outlets require a certain water flow rate.

There are three important considerations to make when choosing the right gas-fired instant water heater for your needs. They are:

Hot water flow rate: 

The amount of hot water that the water heater will produce is directly related to the temperature rise that it needs to achieve. In essence, you must take into account how quickly your hot water appliance can discharge.

The hot water requirement of a typical showerhead is 7 or 8 litres per minute.

 

It is important to note that drench showers provide a variety of hot water flow rates, ranging from 15 litres to nearly any preferred flow rate; flows of 30 litres per minute are not unusual.

 

Kitchen sink taps flow rates: 4–6 l/min.

Modern bath mixer taps demand around 12 litres per minute.

Standard washbasin taps: 4 litres per minute (not spray type).

Basin or cloakroom “spray taps” with a 2-litre-per-minute capacity are popular since they save water,however our gas instant water heaters need 2.5 litres per minute, thus they are not suitable.

You can calculate your hot water demand by adding up all of your hot water outlets and using a diversity factor to account for the fact that not all will be used at once.

Mains cold water temperature for the UK

Your instant water heater should be capable of delivering warm water effectively during the coldest months of the year.

For example, the winter months are when domestic hot water is most needed or employed.

In most parts of the United Kingdom, the coldest mains water system temperature is 10 °C; however, in Scotland, it can drop to as low as 5 °C.

Domestic hot water temperature rise

T° variation is the water temperature rise an instantaneous gas water heater must achieve. This is known as T° variation or delta T, abbreviated as “ΔT.” Simply speaking,the increase in temperature for the required hot water impacts the volume of hot water generated by any gas instantaneous water heater.

To avoid scorching, hot water outlets must be limited to 43°C for saftey. Showering or bath water temperature is gernerally 40°C.

Instant water heaters typically require a 30°C temperature rise (ΔT30) for winter use.

In August, the UK’s hottest month, mains water can reach 20 °C. To meet your hot water needs, the temperature rise is merely 20 °C (ΔT20).

Energy efficient / Energy efficiency

The most energy-efficient gas water heaters are condensing. The condensing process recovers the latent heat that is not recovered by non-condensing water heaters and improves energy efficiency, i.e. condensing instantaneous water heaters reduce the energy required to heat water by recovering heat from exhaust gases to preheat the incoming cold water.

Upon heating, the condensed water and entrapped exhaust gases are effectively and safely discharged into the environment. This is why a condensing gas instant water heater will emit a visible plume from the flue exhaust.

Condensing water heaters are on average 12% to 20% more energy efficient than older non-condensing water heating technology, making them the most cost-effective gas instant hot water heaters to run.

Tankless gas fired water heaters

Tankless water heaters heat water instantly on demand, making them incredibly energy efficient, particularly the condensing models.

Contact us

For more detailed information, stock availability, delivery times ,price or to purchase our cost effective and energy efficient (no energy losses as opposed to a storage hot water system) lnstant gas water heaters / gas instantaneous water heater, as we sell direct our competitively priced instantaneous gas fired water heaters. Please contact our sales team on 01202 822221 or use our site email contact form for your water heater systems requirements with high energy savings.