The government and the industry have heavily promoted condensing combis in the last 20 years and, as a result, some people mistakenly assume that they are the same thing. In fact, there are still many homes with non-condensing combis while almost all modern conventional and system boilers are now condensing too.
The idea of the condensing boiler is simply to reclaim heat from flue gas – mainly in an attempt to meet climate targets. Since 2005, it has been a legal requirement to fit only condensing boilers into new homes or when replacing a worn-out boiler. You can carry on using an existing non-condensing boiler but you will probably only be offered condensing boilers when you need it replaced. There are exceptions for homes that cannot safely accommodate the flues and outflows they require.
Why did the government push combis?
When condensing boilers were made compulsory, it coincided with a new boiler government scheme launched by John Prescott. The government grant scheme insisted on fitting the cheapest boilers and those were combis. The scheme was flawed in some ways and many homeowners dumped good quality system boilers and installed cheap condensing combis inappropriate for their property. For example, some are unable to provide a sufficient flow of hot water for homes with multiple bathrooms. In certain homes, they provide no significant energy efficiency improvement without additional upgrades to thermostats, valves and radiators.
Another new boiler government scheme was launched in 2013 called the Green Deal which included a green boiler scheme whereby some households were helped to fit more efficient boilers. In the same year, the “Energy Company Obligation” (ECO) was launched. This has grown into a complex scheme partly administered by local authorities and partly by energy supply companies.
Your entitlements can therefore vary according to your supplier, your council, the availability of funds, the type of work you need and whether you fall in a priority category. Please call us if you need more advice about your entitlement. Another new scheme called the Home Upgrade Grant may be coming soon.
How the boilers work
The primary heat exchanger is the coil where your water is heated by the combustion of gas. The hot water then goes to your radiators before returning to the boiler. A secondary heat exchanger recoups some of the heat from the exhaust gases before they are vented through the wall. As a result of removing heat from those gases, acidic moisture condenses and must be disposed of to a drain.
The principle is simple, but how efficiently it works depends upon other factors. Returning water needs to be about 45°C – which is cooler than most older plumbing systems were designed to deliver. Adjusting it without turning some of your rooms cold may require careful regulation of the flow rate, radiator valves and thermostats in each room. Boilers that regulate water temperature by switching on and off rather than by graduating their output can also be problematic. Ideally, boilers should also regulate their output according to external weather conditions but most still don’t.
Rather than simply fitting the cheapest possible boiler, it is always wise to have an experienced engineer assess the entire plumbing and heating demands of your home in considering the lifetime cost of ownership.
