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Gas-fired Condensing Water Heaters

1.1           Scope

Gas-fired condensing water heaters are used to provide hot water for domestic purposes or process heating, and offer an energy efficient method of generating hot water. They can be installed close to the point of use, or in a central plant room.

Gas-fired condensing water heaters are described as ‘storage’ type products if they generate hot water by heating water stored within the product itself. Other types of gas-fired condensing water heaters are described as ‘non-storage’ type products, and can be divided into continuous flow type products that are designed to instantaneously generate hot water directly from cold water, and those that heat water as it is circulated round a loop (which may also include buffer vessels).

Gas-fired condensing water heaters are available in a range of different efficiencies. The Energy Technology List (ETL) Scheme aims to encourage the purchase of higher efficiency products.

The ETL Scheme covers three categories of gas-fired condensing water heaters:

1.    Storage type, gas-fired condensing water heaters not exceeding 150kW

2.    Non- storage, instantaneous (or continuous flow) type, gas-fired condensing water heaters

3.    Non-storage, circulator (or multi-pass) type, gas-fired condensing water heaters.

To be eligible for inclusion on the ETL, products shall meet the requirements as set out below.

1.2           Definitions

Gas-fired condensing water heaters are products that are specifically designed to continuously provide hot water either by the direct heating of water as it passes through the product, or the heating of water contained in an integral storage vessel.

1.3           Requirements

1.3.1       Eligibility requirements 

To be eligible products, must:

  • Be gas-fired.
  • Comply with the requirements of the Water Supply (Water Fittings) Regulations 1999, the Water Byelaws 2000 Scotland and the Water Regulations in Northern Ireland (for example, by inclusion in the Water Regulations Advisory Scheme’s Water Fittings and Materials Directory).
  • Have an appropriate Conformity Assessment mark.

In addition, non-storage – circulator type, gas-fired condensing water heaters must:

  • Use fully premixed burners or an appropriately matched forced draught burner (or burners).
  • Automatically respond to changes in hot water demand by modulating their output in a continuous manner across a minimum turndown ratio of 3.33:1, without initiating a purge cycle.
  • Products with a thermal output in excess of 400kW must either use burners from the “burners with controls” part of the Energy Technology Product List or:
    • Incorporate a microprocessor based burner control system.
    • Use a variable speed motor controller (or Variable Speed Drive) to operate each forced draught fan incorporated into the product.
    • Where mechanical dampers are used to modulate the air flow to the burners, they must be operated by a precision servomotor. The servomotor must be controlled by a positional or flow based feedback mechanism that automatically adjusts its operation to correct for mechanical wear, valve stiction and hysteresis.
    • Where control valves are used to modulate the fuel flow to the burners, they must be operated by a precision servomotor. The servomotor must be controlled by a positional or flow based feedback mechanism that automatically adjusts its operation to correct for mechanical wear, valve stiction and hysteresis. (This requirement shall not apply to pneumatically operated modulating gas valves).

In addition, non-storage – instantaneous type, gas-fired condensing water heaters exceeding 70kW must be fitted with an integral, fully pre-mixed, modulating burner.

1.3.2       Performance requirements

Eligible products must meet or exceed the appropriate performance criteria:

  • Products with a rated heat output ≤ 400kW, must meet or exceed the gross water heating energy efficiency ηwh thresholds shown in Table 1.1 at the declared load profile.
  • Products with a rated heat output > 400kW, must meet or exceed the gross thermal efficiency thresholds shown in Table 1.2.

Table 1.1    Minimum gross water heating energy efficiency (ηwh) for gas-fired condensing water heaters with a rated heat output of 400kW or less (all product categories) ​​​​​​

Declared load profile

3XS

XXS

XS

S

M

L

XL

XXL

3XL

4XL

Water Heating Energy Efficiency (ηwh)

≥ 70.0%

≥ 80.0%

≥ 85.0%

 

Where:

  • Water Heating Energy Efficiency (ηwh) is the ratio between the useful energy in the water provided and the energy required for its generation, expressed as a percentage.
  • Load profile is a given sequence of water draw-offs, as specified in in Annex III, Table 1 of Commission Regulation (EU) No 814/2013 “Ecodesign requirements for water heaters and hot water storage tanks”.

Table 1.2    Minimum gross thermal efficiency for gas-fired condensing water heaters with a rated heat output of over 400kW​​​

Product category

Nominal heat input (kW)

Test conditions

Gross thermal efficiency %

Non storage – instantaneous type

> 400kW

At 100% load, flow/return temperatures of 80/60ºC

≥ 85.6%

At 30% load, return temperature of 30ºC

≥ 93.7%

Non storage - circulator type

> 400kW

At 100% load, flow/return temperatures of 80/60ºC

≥ 85.6%

 

At 30% load, return temperature of 30ºC

≥ 93.7%

 “” means “greater than or equal to”

For products with a rated heat output ≤ 400kW, the load profile used for the test must be declared by the manufacturer and shall be the maximum load profile or the load profile one below the maximum load profile for the product.

Products with a rated heat output > 400kW must meet or exceed the minimum gross thermal efficiencies at both full load and part load test conditions, as specified in Table 1.2.

1.4           Measurement and Calculations

1.4.1       Measurement standards

All products must be tested in accordance with the procedures set out in one of the test standards recognised by the ETL as set out below, or in accordance with equivalent procedures for assessing thermal efficiency within applicable British Standards.

Tests to determine gross water heating energy efficiency (products ≤ 400kW) must be carried out at the conditions specified in BS EN 13203-2:2015.

Tests to determine gross thermal efficiency (products > 400kW) must be carried out at the test conditions specified in an appropriate test standard named in Table 1.3.

Table 1.3    ETL recognised test standards to determine gross thermal efficiency ​​​​​

Test standard

Applicable product categories

 

1

2

3

4BS EN 89:2000 Gas-fired storage water heaters for the production of domestic hot water

þ

 

 

BS EN 89:2015 Gas-fired storage water heaters for the production of domestic hot water

þ

 

 

BS EN 303-3:1999 Heating boilers — Part 3: Gas-fired central heating boilers — Assembly comprising a boiler body and a forced draught burner‘.

 

 

þ

BS EN 303-7:2006 Heating boilers — Part 7: Gas-fired central heating boilers equipped with a forced draught burner of nominal heat output not exceeding 1,000kW‘.

 

 

þ

BS EN 15502-1:2012+A1:2015 Gas-fired heating boilers. General requirements and tests

BS EN 15502-2-1:2012 Gas-fired central heating boilers. Specific standard for type C appliances and type B2, B3 and B5 appliances of a nominal heat input not exceeding 1 000 kW

 

 

þ

BS EN 483:1999+A4:2007 Gas-fired central heating boilers. Type C boilers of nominal heat input not exceeding 70kW‘

 

 

þ

BS EN 677:1998 Gas-fired central heating boilers. Specific requirements for condensing boilers with a nominal heat input not exceeding 70 kW

 

 

þ

BS EN 26:1998 Gas fired instantaneous water heaters for the production of domestic hot water, fitted with atmospheric burners

 

þ

þ

BS EN 26:2012 Gas-fired instantaneous water heaters for the production of domestic hot water

 

þ

þ

BS EN 26:2015 Gas-fired instantaneous water heaters for the production of domestic hot water

 

þ

þ

1.4.2       Rounding 

For the avoidance of doubt, all efficiency test data should be presented to one decimal place. As an example, a 500kW non storage, instantaneous, gas fired condensing water heater with a gross thermal efficiency of 85.5% at the full load condition would be deemed to be a fail.

1.5           Verification for ETL Listing

Any of the following testing routes may be used to demonstrate the conformity of products against the requirements:

  • In-house testing – Self-certified
  • In-house testing – Self-tested and verified or cross-checked by an independent body
  • Witnessed testing
  • Independent testing
  • Representative testing (see clause 1.5.1)

Further information regarding the first four routes can be found in Guidance Note 5 on the ETL product testing framework[1].

1.5.1       Representative testing

Where applications are being made for gas fired condensing water heaters that are variants of the same constructional design and rated outputs up to and including 400 kW to be included on the ETL, test data may be submitted for a representative selection of models. The representative models must be selected by dividing the range of products into groups of models with similar design characteristics, and testing a model in the lowest quartile of predicted performance in each group. The performance of each model in the group must be predicted using a validated mathematical model. As a minimum, at least one model must be tested in each range of products.

Where applications are being made for products of the same constructional design and rated outputs greater than 400 kW to be included on the ETL, test data may be submitted for a single representative model provided that the maximum rated output of the products being applied for is not more than twice, or less than half, the maximum rated output of the product tested. Where the range of rated outputs exceeds these limits, products should be grouped into size ranges that comply with these rules, and test data submitted for one representative model for each group.

It should be noted that:

  • If a manufacturer voluntarily removes a representative model from the ETL then other products linked with that representative model may or may not be permitted to remain on the ETL.
  • If any product submitted under these representative model rules is later found not to meet the performance criteria when independently tested, then all products based on the same representative models will be removed from the ETL.

1.6           Conformity testing

Products listed on the ETL may be subject to the scheme’s conformity testing programme in order to ensure listed models continue to meet the ETL requirements.


[1] https://www.gov.uk/government/publications/energy-technology-list-etl-product-testing-framework