To not be able to work out the best way to heat my house?!

[TeaLightsGlisten]

I feel silly, but I need advice, and I know there's so many financially savvy people on here.
I live in a very small 3 bed semi. The entire house both upstairs and downstairs is only 85 metres squared in total.
I have a multi fuel burner downstairs and I use smoke free fuel in this to heat the whole of downstairs. It works well. I don't put it on until 4pm as we're all out of the house until then. The heat generated from this heats the downstairs living space well.
We have gas central heating installed, but we do not use the radiators downstairs because we only use the multifuel stove burner to heat downstairs, which is only 42.5m2 of space.
This has been fine till now, we haven't switched the central heating on at all yet this year.
However, temperatures are dropping and I am beginning to notice a cold, damp smell in the upstairs bathroom and in 2 of the bedrooms, and these rooms are starting to get uncomfortably cold now. 1 of the rooms is DS's who has bad asthma. The other room is mine, also bad asthma. So I need to ensure these bedrooms are kept warm.
What I can't work out is, would it be cheaper to turn on the central hear from 4pm - 9pm but turn off all the downstairs radiators at the valves, so that only the upstairs radiators come on. Or would it be cheaper to use oil filled electric plug in radiators in the 2 bedrooms and pay gor a wall mounted electric towel rail and have that switched on in the bathroom? Again, the electric heaters would be switched on 4pm - 9pm.
Basically, what's cheaper to run....gas central heating with only the upstairs rads turned on, or 3 separate electric oil filled plug in heaters?
Is a gas boiler cheaper to run if half the rads are turned off, or does it cost the same amount of money to run the gas boiler regardless of how many rads are turned on?
I'd live some advice. I really need to be careful with heating costs, but I'm clueless as to what to do for the best!😔

Sorry for the typos in my post...🙆

I think gas is much cheaper than electricity. I don’t have the figures but have lived in a house with central heating and a house with electric storage heaters, and central heating was much cheaper.

With central heating the cost is warming up the water in the radiators, and warming it over and over again as it gets cooler because its heat transfers to the rooms. If you have fewer rooms to warm up, it will cost less. This of course assumes that you either have a thermostat in one of the rooms you are heating or turn the radiators off when the rooms are warm enough. You might find that an hour in the evening eg 4-5 is enough and you don’t need them on 4-9.

I would try that and measure the costs before buying any new expensive equipment such as oil radiators, tower racks etc.

Where is the thermostat and which radiator you cannot turn off in order to protect the pump? In my home that’s the rad in the living-room. Got thermostatic valves in the bedrooms?

As mentioned by LegoDeathTrap; gas is cheaper than electricity

Irrespective of turning the rads off, the hot water still does the whole system

My instinct would say turn off radiators in the rooms you don’t need it but run the gas central heating rather than using electric, I’m sure that would be cheaper for you.

I just have the radiators programmed to turn on an hour before everyone gets up and then an hour before bed upstairs. And like you I use a burner for downstairs

Beware of mould if you don't heat your house much. Last year I lowered the heating and we got a lot of mould. This year I'm going to spend a bit more on heating.

Would electric blankets on beds help at all?

Central heating will be cheaper than the electric powered heaters and you shouldn’t need it on 4-9. Do you have a thermostat? Once up to temp upstairs it should turn off and only click back on when needed rather than being on constantly. If not, at least buy a timer so you can set it to be on for 30 mins off for 30, using it less but maintaining temps

Should have added it is easier to keep the room at temperature than allow it to go stone cold then try and heat it. With yours and your sons asthma I would prioritise heating the whole house over other spends (if this is possible) as it will make a big impact on his long term health

Heating a room by electric heaters is easy to calculate. 3 heaters at let’s say 2000 watts all on at the same time will get through 6000 watts per hour If your electric units is let’s say 10p per Kw hour that will cost you 60p per hour

Thank you all for your advice🙏

If you have the gas central heating on use the radiators downstairs instead of the stove.