How efficient were old gas appliances ?

[KeithSModerator]

I was led to ask this question because our old gas fire and back boiler was rated at 11.7 kwatts.  British Gas when they installed it, ( in the early 80’s )  knocked a large hole in our living room wall so that in our living room we had a large fire at one end and a large hole at the other.  Given the large quantities of hot air leaving, and equally large quantities of cold air coming in just how efficient could it have been ?    30% maybe ?     The hole has now been blocked ( and insulated ) , and the fire has been replaced by an air to air heat pump which uses by my rough calculations about 3/4 of a kilowatt and keeps the whole house warm.   British Gas might morn its demise but I certainly dont.

[GordonGKeymaster]

I had a similar  set up in the house we rent. When the old gas fire and back boiler were eventually stripped out, a chimney balloon inserted, and a new Vaillant combi installed, the comparative efficiency was very evident in how much quicker the house came up to temperature once the heating came on. The improvement was dramatic. We suddenly felt like we were in heaven! Also, getting rid of the gas fire meant we could allow ourselves the luxury of slapping some bubble wrap over the old core vent in the wall – cutting out some seriously cold draughts.

Not sure on the efficiency of old boilers (I’ve read 65%) but I think towards the end of their life they can be a lot less – when the burner is all coked up etc as was the case with the one in our house.

[MartinNModerator]

The efficiency of  ancient boilers like your late back boiler is in the range 50 to 60%, but I think that is before allowing for the draughts through the massive hole.  Old gas fires can be as low as 30%.

Where you need a b*** great ventilation hole for an appliance which is not the main heat source the efficiency could be negative, i.e. the heat loss thru the hole 24/7 is more than the heat you get from occasionally running the appliance. You could close the hole when the appliance is not running, but if you forget to  open it when the appliance is on you could possibly die from the fumes; that is why Bldg Regs require the hole to be non closable. It is also one reason why all modern boilers are balanced flue, i.e. they have their own built in air intake, so no separate vent is needed. A few wood burning stoves have the option of an attached air vent.

[Boiler EngineerParticipant]

Old standard-efficiency boilers can waste over a third of the energy they produce. Modern high-efficiency boilers can be 90% efficient. Upgrading to a condensing boiler can save as much as 40% on your heating and hot-water bills

An A rated boiler is the most efficient, with efficiency at 90 percent or higher. All A rated boilers have a stamp of approval from the Energy Saving Trust.

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