Single-point heaters, located at the point of use and serving only one outlet, do not have distribution losses. Gas multipoint water heaters and instantaneous combi boilers are also instantaneous types but, as they normally serve several outlets, they are assumed to have distribution losses.
Stored hot water systems can be served by supplementary electric water heating or obtain heat from a boiler, room heater, solar heater, or heat pump through a primary circuit. In either case, water storage losses are incurred to an extent that depends on how well the water storage is insulated. These losses apply for the following categories of heating equipment:
Water storage losses are set to zero for instantaneous combi boilers and some instantaneous electric water heaters. Where an instantaneous electric water heater contains storage, add this storage volume to the hot water storage volume in DEAP. Heat gains are allocated to the dwelling from the hot water storage in cases where the cylinder is within the heated dwelling space.
For cylinders, the preferred way of establishing cylinder losses is from measured data according to BS 1566 or IS EN 12897. Cylinder standing losses may also be stated on an NSAI Agrément Certificate or equivalent.
The cylinder loss stated on labels / nameplates can be used where:
For thermal stores and CPSUs (including electric CPSUs) the preferred way of establishing heat losses is from measured data on the thermal store or CPSU concerned. If measured data is not available, a default value is used; this is calculated on the water heating: options and storage tab based on insulation type and thickness and cylinder volume.
In all cases, the loss rate is to be multiplied by a temperature factor from Table 5.1 This factor accounts for the average temperature of the cylinder or thermal store under typical operating conditions, compared to its temperature under test. Hot water storage volume is determined using the guidance in Table 5.2.
For combi boilers the storage loss factor is zero if the efficiency is taken from Table 4.5. The loss is included for a storage combination boiler if its heating efficiency is based on certified data or is obtained from the Home Heating Appliance Register of Performance (the HARP database), using the calculated hot water storage loss factor and volume on the water heating: options and storage tab and the temperature factor from Table 5.1 below. The insulation thickness and volume should be provided by the manufacturer or obtained from HARP.
| Type of water storage | Temperature Factor | |
|---|---|---|
| For manufacturer’s declared loss | For calculated loss | |
| Cylinder, immersion main water heater | 0.60 | 0.60 |
| Cylinder, indirect | 0.60 a) b) | 0.60 a) b) |
| Storage combi boiler, primary store | n/a |
Store volume ≥ 115 Store volume < 115 |
| Storage combi boiler, secondary store | n/a |
Store volume ≥ 115 Store volume < 115 |
| Hot water only thermal store | 0.89 c) d) | 1.08 c) d) |
| Integrated thermal store and gas-fired CPSU | 0.89 c) d) | 1.08 c) d) |
|
Electric CPSU: Winter operating temp.
|
|
1 in all cases |
| Plate heat exchanger in a group heating system | 1 | 1 |
Notes:
a) Multiply temperature factor by 1.3 if a cylinder thermostat is absent.
b) Multiply temperature factor by 0.9 if there is separate time control of domestic hot water (boiler systems and heat pump systems only). A switch for summer/winter operation of space heating with a single timer shared between space and water heating is not considered to be separate time control of domestic hot water.
c) Multiply temperature factor by 0.81 if the thermal store or CPSU has separate timer for heating the store.
d) Multiply temperature factor by 1.1 if the thermal store or CPSU is not in an airing cupboard.
e) Where it is unclear if a storage combi boiler has a primary or secondary store, assume primary store present.
Where none of these notes apply, the temperature factor and associated multiplier default to 1
| (mm) | Height (mm) | Storage volume |
|---|---|---|
| 300 | 1600 | 96 |
| 350 | 900 | 72 |
| 375 | 900 | 84 |
| 400 | 900 | 96 |
| 400 | 1050 | 114 |
| 450 | 675 | 84 |
| 450 | 750 | 95 |
| 450 | 825 | 106 |
| 450 | 900 | 117 |
| 450 | 1050 | 140 |
| 450 | 1200 | 162 |
| 450 | 1500 | 206 |
| 500 | 1200 | 190 |
| 500 | 1500 | 245 |
| 600 | 1200 | 280 |
| 600 | 1500 | 360 |
| 600 | 1800 | 440 |
Notes:
Determine the hot water storage vessel volume using one of the following steps:
a) Measure the height and diameter of the hot water storage vessel and choose the nearest height and diameter options from Table 5.2 to determine the volume in litres. Insulation thickness should not be included in the height or diameter measurement when using the table above. Table 5.2 is based on BS1566 and applies to copper cylinders; however, these figures may also be used for other types of storage vessels for the purposes of DEAP assessments. In some cases, the cylinder or storage may be clearly much larger or much smaller than the values in Table 5.2. In such instances, and in the absence of other information on labels or technical data based on relevant standards, the volume of a cylinder can be calculated by recording both the cylinder height and the diameter of the cylinder. The volume (which applies to hot water storage only) is then calculated as follows:
V = (pi x d2/4) x h / 1000
Where:
b) The storage vessel diameter may be determined based on vessel circumference, dividing the circumference by π (3.14), before following step (a) above. Diameter should not include insulation thickness.
c) Alternatively, the hot water storage vessel volume may be determined from Agrément certificates or a label on the vessel, provided the label also references a European or national standard (such as BS1566 or IS161) or is CE marked. While labels are regularly available on hot water storage vessels, they do not always show a relevant standard or CE mark.
d) Where the hot water storage vessel is inaccessible:
For new-final BERs, documentary evidence from the installer, developer, architect, or engineer identifying the volume of the installed vessel may be used.
For existing dwellings, the following defaults apply:
For existing dwellings, where hot water cylinder insulation is not accessible, assume the following:
In the case where the storage is retrofitted after the dwelling was constructed, the storage volume’s age rather than dwelling age is relevant when determining the default insulation thickness. Where the storage volume age is unknown, it should generally be assumed to have been installed when the dwelling was constructed. If the dwelling was constructed prior to 2000 and the cylinder has been clearly retrofitted more recently, 35 mm of factory applied insulation should be assumed.
Where multiple hot water cylinders are present in a dwelling the average insulation thickness is determined using the weighted volume of each cylinder. Where there is a storage unit with a lagging jacket and a unit with factory insulation, the lagging jacket insulation is considered to be half as effective as factory foam insulation. Therefore, the thickness of the lagging jacket is multiplied by 0.5 and treated as factory fitted insulation. This average factory insulation thickness weighted by volume is then calculated.
For heating systems with separate hot water storage, such as boilers or heat pumps, primary losses are incurred in transferring heat from the heat generator to the storage; values for primary losses are obtained from Table 5.3 below. The primary circuit losses for combi boilers are specified in the combi boilers section.
The efficiency for both space and water heating is reduced by 5% if a gas or oil boiler is not interlocked for both space and water heating (See heating controls in section 4).
| System type | kWh/year |
| Electric immersion heater | 0 |
| Boiler / heat pump with uninsulated primary pipework* and no cylinder thermostat | 1220 |
| Boiler / heat pump with insulated primary pipework and no cylinder thermostat | 610 |
| Boiler / heat pump with uninsulated primary pipework and with cylinder thermostat | 610 |
| Boiler / heat pump with insulated primary pipework and with cylinder thermostat | 360 |
| Combi boiler | 0 |
| CPSU (including electric CPSU) | 0 |
| Boiler / heat pump and thermal store within a single casing (cylinder thermostat present) | 0 |
| Separate boiler / heat pump and thermal store connected by no more than 1.5 m of insulated pipework | 0 |
|
Separate boiler / heat pump and thermal store connected by:
|
|
| Community/ Group/district heating | 360 |
+ References to “boiler” in this table also imply other wet heating systems such as heat pumps.
* “Primary pipework” means the pipes between a primary water heater and a hot water tank.
** When specifying that the primary pipework is insulated, bear in mind that this refers to all of the pipework between the primary water heater and the water storage, including joints and bends but excluding elements such as motorised valves or pressure gauges. Where some of the pipework is not visible (if for example it runs through walls or floors), then it must be assumed to be uninsulated unless it can be proven to be insulated.