Cost question Gas fire V Central heating.

TimSynths

I have a 23kwh Combi Boiler supplying 4 radiators. I also have a gas fire in the lounge which I rarely use but with recent events and after a conversation with a neighbour I said I would endeavour to find out the cost of using it. 

The fire is a Baxi Kingston 2 classic.

Would I be correct in thinking that it will use 6.16kw of gas in an hour? I would only have it on the lowest setting as it does kick out some heat. Should I just heat that one room as opposed to having the heating on cost effective wise?

Its not a case of I cant afford the heating I just now want to know what's best to do- look after the pennies and all that.

TimSynths

Found this online so I assume that on its lowest setting it will be consuming 2.4kwh- I think.

wittynamegoeshere

The consumption doesn't really matter, the efficiency is what matters, i.e. how much heat you get in the house per unit of gas.

I think yours is an open gas coal-effect one, they're incredibly expensive to run, or even to have fitted at all.  In my opinion these things are ridiculous, clearly they were invented when energy was extremely cheap.  Much of the heat goes up the chimney plus the opening is basically the same as an open window - it will cost you lots in extra heating even when off.  We had one in our previous house, I stuffed the top of it with a bag full of packaging and the entire house was instantly vastly warmer.

Just ensure you do something obvious to ensure nobody lights it if you block it.  If you're going to use it occasionally then probably best to not block it at all.  You will probably find you don't need it once you close it up, it is probably the reason you're cold.

There are specific products for blocking chimney openings, some of which have hanging warning signs.  You'll never have a warm house while there's a whacking great hole in the roof ducted directly into the living room.

Your fire will probably be around 50% efficient, while your boiler should be 90%+ efficient.  Also, while your fire is throwing half your money out of the chimney, in addition it will also be creating a vacuum that will be drawing in cold air elsewhere in your house, e.g. draughts in window frames, gaps in floorboards etc.  Sometimes a fire can make a room colder than without it!

I'd suggest sealing it up temporarily, if this does improve matters than look at getting a new fire, one that isn't basically a hole in the wall.

tim_p

We live in a gas centrally heated bungalow and also have a gas fire. We tend to use the fire on its lowest setting and it heats the whole house (most rooms used, doors left open) 
do your own testing, read the meter, leave fire on for a few hours, read the meter again.
it certainly works for us (gas around 7000 kWh / year) 
Heating is always on in the (winter) mornings but often doesn’t fire up late afternoon. 

Try it, only you can decide if it works for your situation. 

Gerry1

TimSynths said:

The fire is a Baxi Kingston 2 classic.

Would I be correct in thinking that it will use 6.16kw of gas in an hour?

No.  If it's on the maximum power setting it will use 6.16kWh of energy in one hour.

However, the real message on that warning label is that you're putting in 6.16kW but only getting 4.0kW of heat out, a massive 2.16kW going straight up the chimney ! 

That's just 65% efficient.  Your combi boiler is likely to be around 90% efficient or more, especially if correctly set up so that it's condensing.

TimSynths

Thank you all for the amazing answers- this is exactly the sort of feedback I was looking for.

savers_united

Your combi is not going to be using anywhere near 23kwh if you only have 4 radiators. Radiators tend to be around 2kw each, smaller ones obviously less and bigger ones use more.

So in theory even with all your rads on max setting they could only use 8kwh but it will be less than this, especially once the system is up to temperature, the boiler will modulate the output to maintain the flow temperature. 

I have 15 radiators and a 32kw boiler, and even on start up from cold the first hour is never more than around 14kwh used.

Many older fires have no temp control so just stay on high or low all day until switched off. 

We have a 85%+ Efficient kinder Gas fire that has remote control where you can set the temperature and you actually see the flames drop down when it approaches target temp, it's a sealed unit so no chimney draught.

Staffordian11

Gas fires vary hugely in their efficiency. The model the OP refers to is about 60% as others have stated, some achieve closer to 80% or more, whilst some - the living flame type with no glazed fronts etc throw more heat up the flue or chimney than they put into the room. And when not in use allow quite a bit of the heat within the room to escape and allow cold draughts into the room down the flue.

As an example, when we moved to our current property I carefully monitored monthly gas and electricity consumption and soon found that it was as expensive to keep just the lounge warm with the open, living flame gas fire as it was to keep the entire property warm with the combi boiler.

wrf12345

Radiant type gas fires are the ones to go for, more efficient as it is throwing most of the heat into the room rather than up the chimney. Unfortunately gas safe engineers are not keen on fitting gas fires for some reason so it is probably only viable if one comes with the house. Continuous use on the lowest setting for one room will be cheaper than heating the house with CH, a lot cheaper if the boiler is one of the old types. I have lived in houses where I had the old boiler disconnected and just used the gas fire with electric shower and no hot water without any problems but then I actually like sleeping under a couple of duvets in a cold bedroom. I had a radiant electric wall heater in the shower room as well but that was 300W for twenty minutes a day in winter so not expensive to run, and it worked very well in such a small room. The one downside, nowhere to dry towels! These days I have a combi boiler with the hot water turned off (by tap in the pipework) and have a cold shower every morning, wonderful way to wake up once you get over the fright of it, and saves £200-300 a year. Women friends are not amused!

wittynamegoeshere

Most common gas fires are designed to be just under the maximum permitted before you need ventilation.  If you go beyond this then you need a vent straight through the wall elsewhere in the room, so then you have two holes in your living room so things are even worse.

Be extremely careful with gas fires if you have a kitchen extractor.  In our last house we had an open gas fire that, as normal, didn't need an air vent.  if I put the kitchen extractor on full it would pull air down the chimney as a result of the suction it created.  Modern houses don't have many draughts, so the air comes in the easiest route.  If the fire wasn't lit it would just make the room cold and smell horrible.  If the fire was lit then it was probably very dangerous, so I avoided doing this.

I's suggest that the manufacturer's figure of 65% effficiency is probably not achievable outside of a lab.  In reality it's likely to be lower, below 50% is likely and that doesn't include the additional chill that results from pumping all that air out of the roof, so cold air has to be drawn in elsewhere.

It's quite crazy how people go around draughtproofing and insulating while having one of these things.  I'd highly recommend anyone with one fitted just to try sealing it up for a day or two and find out for yourself just how much warmer your house could be without it.

wrf12345

Yes, pigeons used to love my chimney in the winter and would have moved in if I had not kept throwing stones at them.