Switching from coal central heating to Gas central heating

Hi All,

New to this forum so apologised if I have put this in the wrong forum?

I am moving into a 3 bedroom mid terrace house with coal boiler and coal central heating. There is a separate boiler in a boiler room.

I would ideally want to change this to use gas as well as the cooker, oven etc…

Just want to have an idea roughly the cost I may be looking at? I am waiting for a quote for main gas connection. 

The main questions are:
1. Will I have to change the coal boiler?
2. Will I have to change the cooker and oven?
3. Will it be possible for me to keep existing boiler after being connected to gas? 
4. And the general cost I am looking to have a gas central heating rather the coal really?

Sorry if these questions are daft but I have never had to do this and cannot seems to have a step by step information on what I will need to do and a rough cost involve.

thank you :)


  • lohr500
    lohr500 Posts: 964 Forumite
    First Post Name Dropper First Anniversary Combo Breaker
    I cant help with all your questions, but I can try with some.

    1) Normally you would remove the old boiler and replace it with the new one. I am not aware of any conversion kits to convert a coal boiler to gas, but they may exist. Undoubtedly, even if they do, a modern condensing purpose built gas boiler will be far more efficient than fitting some sort of conversion kit to your existing boiler.

    It may be possible for the installer to leave your old boiler in situ whilst also fitting a new gas boiler, giving you the flexibility of burning coal if you wanted to in the future. However, this would involve more complex plumbing and additional cost. Personally, if I was switching from coal to gas, I would want the old boiler removing to free up space.

    2) What are you cooking with now? As you have no gas, I am guessing you must be using electric unless you have a coal fired range. No need to change either as the gas boiler operates independently. You might want to consider a gas hob and oven, but this would add additional expense from the gas pipework that would be needed and the cost of the appliances. Again, personally, I wouldn't bother.

    3) See my comments in 1) above

    4) Difficult to answer but as a guide, according to this website which may or may not be accurate, 1Kg of house coal produces around 7.0 kWh. A Kg of anthracite produces 9.2kWh.  https://www.directstoves.com/resources/guide-to-solid-fuels/
    Some of that output will be lost through the inefficiency of your coal boiler. My understanding is that gas is going to be around 11 pence per kWh from January.

    How much are you paying now per Tonne of coal and what quality are you buying?
    If you take the cost per tonne, divide it by 1000 and then divide again by 7 or 9.2 depending on if you are using house coal or anthracite, it will give you the coal equivalent cost per kWh. This is before allowing for any efficiency loss from either the coal or a new gas boiler. I imagine the efficiency loss from an old coal boiler will be much greater than the +/- 10% seen on a modern gas condensing boiler. Do you have the make/model of your coal boiler and is there any documentation stating its efficiency?

    I am no expert on coal to gas boiler changes, so the above may not be the most reliable information. But it may help and hopefully others with more knowledge will contribute. 
  • ruthcarr
    Thank you for your detailed reply. I haven’t gone to live there yet so I have no idea how much it will cost running coal boiler.

    From your information, it looks like I will have to look into a new gas boiler to replace the coal boiler. 

    Would you know if I may have to replace the radiators as well ? The property have radiators already running on coal of course.
  • lohr500
    lohr500 Posts: 964 Forumite
    First Post Name Dropper First Anniversary Combo Breaker
    It will probably depend on the size of the radiators.

    For a gas condensing boiler to work efficiently, the water returning to the boiler after it has gone round the radiator circuit needs to be below 54C. Below 54C the boiler begins to work in condensing mode, improving efficiency. The lower it can get below 54C, the more efficient it becomes.

    However, generally speaking without getting bogged down in detail, to run at a lower return temperature the water leaving the boiler flowing to the radiators also needs to be at a lower temperature.

    With cooler water flowing through the radiators they need to be large enough to dissipate heat effectively into the rooms.

    I would imagine an old coal boiler will run with hotter flow/return temperatures and so the radiators may have been sized to take this into account. But they could be fine with a gas boiler.

    Whoever installs the new boiler should be able to look at the size/design type of the radiators and calculate if they will be large enough.

    They will also no doubt want to flush out the old radiators and pipework prior to installing the new boiler. This is standard practice and for some new boilers, the guarantee is dependent on the system being flushed/filled with a corrosion inhibitor and an in-line magnetic filter fitted. 
  • ruthcarr
    Thank you soo much for such detailed information. That’s enough to start me off :smile:
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