EOGB commissioned an approved test house to undertake an independent test, comparing Sapphire to a market leading oil boiler.

There has long been discussion and negativity towards modulating domestic oil and often dismissed by manufactures who stated there were no clear advantages over modulating oil systems compared to traditional on/off technology.

This may be the case for a standard test of Boiler efficiency, but its overall system efficiency we are interested in.

What are the advantages of integrating OpenTherm smart controls that only deliver the required amount of heat actually needed to heat your home?

In Order to prove this theory EOGB commissioned an approved test house to undertake an independent test to compare a market leading oil boiler and an EOGB Sapphire modulating boiler.

A whole house simulator rig was used, which happens to be the same rig used for Heat pump efficiency testing also. 

Two tests were done per boiler one for typical April temperatures and one for February Typical temperatures the testing rig allows extremely accurate results as the temperatures for each type of boiler test are identical so leaves no doubt over the results. 



EOGB Sapphire uses and modulates using the OpenTherm protocol, so is compatible with all OpenTherm thermostats such as Honeywell Evohome, Genius Hub, Nest and Danfoss to name a few.

The Testing Program

Both Boilers were set to identical output of 20KW and the design condition were based on the CIBSE guide with a design Temperature of -2 degrees Celsius outside and and internal Temperature target of 21 Degrees Celsius internally and a property heat loss factor of 600 W/K.

This give a heat loss rate of 13800 W at design conditions and represents a large not very well insulated property that are common place in the UK especially in off gas grid rural locations. 

The tests are carried out against outside temperature profiles (see figure 1) These profiles represent and average UK winter day and an average spring day. This data is then added to the program which then calculates the cooling load. The heating system then is enabled and performs against the simulated conditions as it would in normal circumstances in a property. 

Results Summary

  • EOGB Sapphire Boiler showed a significant reduction in oil consumption whilst maintaining the same internal temperature conditions within the property, compared to the standard condensing boiler set to an identical 21 degrees on an identical property simulation
  • Depending on the OpenTherm thermostats used on Sapphire, we found up to a 17% reduction in fuel consumption
  • The overall electrical consumption was reduced by 66% when running on Sapphire, compared to the standard condensing boiler  



The Figure below shows the Sapphire operating using the Genius Hub OpenTherm controls on a cold February day, and the green section can be clearly be seen. This indicates the modulation rate of the boiler.

The red line is the internal thermostat set point. It can be seen that the boiler modulated to maintain this set point at a reduced fuel consumption rate rather than constant on/off cycling seen with standard boilers.