Oil filled radiator help please

Dartfordian

Which are saying that oil filled radiators are the most economical portable heater (I would post a link to the page but as a new member on the forum I'm banned from doing so - look for a page headed "Portable heater reviews: Features explained"). We have two and, while I didn't know for sure if they saving us money, we have been pleased with the way they heat up a big conservatory and a room that doesn't have central heating or double glazing. We have two Airforce 2500W's. You can set them up to turn off and on when you want, as well as a thermostat.

What I don't know is if it would be worth extending our gas central heating into these rooms. It would mean getting a new hot water tank as the current one isn't big enough (or an extra tank as there's no room for a bigger one where it is).

Bobzilla_2

The reason this gets so divisive is because the answer varies depending on usage.

Yes gas is about 3x cheaper than electric, but there are numerous factors to consider aside from just the cost of a kw of gas.

The efficiency of your boiler for a start even the best most modern boilers cannot get much over 90% efficiency, the age and condition of your radiators (systems do sludge up reducing the effectiveness and efficiency), the positioning of radiators (so much heat escapes your house through windows - so if you have a radiator underneath a window it will be incredibly inefficient), the running costs of your boiler (for the pump, switches and fan assisted flue), maintenance and servicing costs etc.. there's also the likelihood that you are paying to heat rooms that are empty. Cost aside, there's also the issue of safety from gas leaks, burst heating pipes and carbon monoxide escapes.

By contrast an oil radiator can be placed in the room in which you are sat for most of the time (usually the living room). It is 100% efficient (1Kw of electricity creates 1Kw of heat unlike boilers that convert gas into heat, light, radiation, sound etc..). And what nobody has really mentioned - oil rads intentionally short cycle. That is, they frequently cut on and off. I have a 2.5kw oil radiator that, on full heat, on a cold day, cycles on for about 3 minutes and then shuts off for 6. It keeps the room pleasantly warm but cuts running costs by two thirds. The oil holds the heat and the radiator spews out warmth - but it uses no power at all for the majority of the time. Do that with a gas boiler and you'll drastically reduce the life span of a lot of the internal components.

In terms of numbers - at 15p kw/h - my oil rads run in short bursts for about 20min an hour so it costs about 5p an hour to run and keep a good sized living room warm.

I would add that despite everything I've just said, under certain situations - it is cheaper to use gas - but an oil rad strategically placed can still save on heating bills. Even in a large house - you can leave one on in the living room (shut the radiators off in there) and just use the gas heating overnight.

Smiley_Dan

Bobzilla is correct. Same thing applies to DHW when considering an immersion at the top of the tank or using gas to heat the whole tank. You have to consider the energy used as well as how much the creation/import of the energy costs.

Cardew

Bobzilla wrote: »

I have a 2.5kw oil radiator that, on full heat, on a cold day, cycles on for about 3 minutes and then shuts off for 6. It keeps the room pleasantly warm but cuts running costs by two thirds.

I understand the thrust of your post, but that statement is liable to misinterpretation and your statement below is completely wrong:

In terms of numbers - at 15p kw/h - my oil rads run in short bursts for about 20min an hour so it costs about 5p an hour to run and keep a good sized living room warm.

You have a 2.5kW heater, at 15p/kWh it would use 37.5p an hour if on all the time. As it is only on for 20 mins in the hour it will cost 12.5p an hour not 5p an hour.

Stating it 'cuts running costs by two thirds' is meaningless unless we know what running costs you are comparing it with.

A 2.5kW heater on for 3 mins and off for 6 mins simply means that the room needs 0.833kW to maintain the required temperature in the room; and will cost 12.5p an hour.

If you only had a 1kW heater in the room it would be on for 50 mins, and off for 10 mins in the hour and produce exactly the same heat, for the same running cost,(i.e 12.5p an hour) as your 2.5kW heater.

Having 1kW, 2kW, 3kW, or 6kW of heating in the room doesn't mean you cut any running costs, the output of those heaters to maintain the required temperature is exactly the same at 0.833kW and costs 12.5p an hour.

matelodave

Cardew is absolutely correct - the amount of heat a room requires is determined by the amount of heat it loses through the walls, windows, ceiling floors and by draughts.

The size of the heater will only determine whether it will actually heat the room and how long it will take to get to the thermostat set temperature. Once it's achieved the temperature it will switch off until the room temperature has dropped enough to require more heat

The colder it is outside then more heat gets lost and it therefore requires more to maintain the same internal temperature.

If you do the sums then you can determine the optimum size of heating appliance that you need - it's easy to get one that's too small. A bigger one won't cost more to run as the thermostat will control the amount of heat you require.

If you assume that your room loses 100wh per degree of temperature difference then to keep it at 20 degrees when its 10 degrees outside will require 10x100 = 1kw heater and it will be on all the time whereas a 2kw heater will only be on for 50% of the time but will still produce the require 1kwh.

However when the outside temperature drops to 0 outside you'll need at least 2kw on all the time. The 1kw won't be enough to keep you warm - in fact it will only keep the room at 10 degrees.

It's important that you get a heater that's big enough to heat the room when it's very cold outside. The thermostat will control the amount of heat you need to maintain the desired temperature. Too small and it will be on all the time and you'll still be cold.

Cardew

Bobzilla wrote: »

the positioning of radiators (so much heat escapes your house through windows - so if you have a radiator underneath a window it will be incredibly inefficient), .

Where did you get this information?

The correct siting of the heating circuit, the pipes, convectors and radiators, is fundamental to the performance and efficiency of the central heating system. It should be your main design consideration.
•Fit convectors/radiators around exterior walls, this creates an even temperature without hot and cold zones.
•Fit convectors/radiators under each window. This will reduce heat loss, cold draughts and condensation.

Radiator - positioning

Generally speaking it’s best to fit radiators beneath the windows of a room. The reason for this is two fold.

Firstly, cold air falling by the window will be balanced out to some extent by the warm air rising from the radiator. Fitting them on the opposite wall can actually cause a noticeable draught, since warm air rising on one side of the room and cold air falling at the other exaggerates the flow around the room.

Radiators work best when positioned in the coldest part of the room e.g. on an outside wall or under a window. If you haven't got enough space for the size of radiator you require, two smaller radiators could be the answer.

'Google' positioning radiators.

Gloomendoom

Bobzilla wrote: »

The reason this gets so divisive is because the answer varies depending on usage.

Robwiz

Cardew wrote: »

Where did you get this information?

'Google' positioning radiators.

A lot of the 'rule of thumb' ideas about heating system design predate energy efficiency and improved building insulation.

We know that fabric heat losses are proportional to the temperature difference between inside and outside. So heating the inner face of an external wall to 55º C with a radiator is going to increase that temperature gradient - if the radiator is fixed to an inside wall, the inner face of external wall will only be at room temperature, say 21º C. So heat is lost at a lower rate.