Electric heater comparison

danrv

matelodave said:

If thats your plan then just dont look at costs - you need to know how much you use in kwh, not £££'s.

Read your meters at least twice a day for a few weeks, before you go to bed when most stuff is off and in the morning before you start turning stiff on, so you can get a view of you day/night consumption especially if you've still got your hot water on off-peak. Its the only way you can determine whether a single rate tariff will work for you.

 However  don't be surprised if your electricity bill sky rockets whilst you are using "on-demand" heating on an off peak tariff because peak rates ae generally around twice the cost of the off-peak one although you do have the flexibilty of only heating one room at a time.

Thanks. Good point about kWh usage. 
The cost is irrelevant as that’s down to the unit price.
I’ll take readings regularly and keep check on usage. What I was finding with the warm air heater was that I was heating the whole house and rooms I didn’t need to.
I know that rooms need to be kept at a certain temperature and with the convectors, as you say, there’s more flexibility.
Lifestyle is a factor also.

danrv

Mickey666 s

Oil-filled electric radiators can't change the basic efficiency and if it uses 2kW of electricity then you'll get 2kW of heat from it.  The oil will take a while to fully heat up when switched on but it will also take a while to fully cool down when switched off, so there will be a time lag for the heat to be released, which may or may not be convenient but it won't change the overall efficiency.

Thanks.
Yes, it depends how you want the heat delivered.

danrv

Heaters are working well heating the small and medium rooms. The mechanical thermostats are a little noisy for bedroom use but all cheap convectors use these.
The open plan hallway with stairwell needs a fair bit of power to keep warm so leaving that for now.
Would probably need a 2kw rad there to fill the space.

Not heating that area isn’t going to help give an accurate account of kWh’s required but I think a storage heater is best as it needs to heat two levels. 
Could do with a two meter arrangement with E7 for hallway storage heater and hot water and normal rate one for individual rooms.
This way, I don’t need to rewire the whole house for E7. I have a switched circuit already in place for the warm air heater. 

matelodave

Generally you'll find that E7 tariffs have much higher peak costs than off-peak so you need to balance out your peak/off-peak use to see how it compares with a single flat rate especially if most of your heating is being carried out during peak rate periods. Getting cheap hot water may not be cost effective if you are paying over the odds for all your other consumption. So you need to know when you are using your energy and how much you are using during the peak and off peak periods.

We are all electric, heating, hot water, the whole lot but I cant shift enough to off-peak periods to make an off-peak tariff worthwhile,,so we are on a a cheap single rate tariffs (the same one as Gerry). Even our hot water only uses around 2kwh a day
I've tried to persuade SWMBO to do the washing, ironing and hoovering between midnight and 7 am but she's put her foot down with a firm hand.

danrv

matelodave said:

Generally you'll find that E7 tariffs have much higher peak costs than off-peak so you need to balance out your peak/off-peak use to see how it compares with a single flat rate especially if most of your heating is being carried out during peak rate periods. Getting cheap hot water may not be cost effective if you are paying over the odds for all your other consumption. So you need to know when you are using your energy and how much you are using during the peak and off peak periods.

We are all electric, heating, hot water, the whole lot but I cant shift enough to off-peak periods to make an off-peak tariff worthwhile,,so we are on a a cheap single rate tariffs (the same one as Gerry). Even our hot water only uses around 2kwh a day
I've tried to persuade SWMBO to do the washing, ironing and hoovering between midnight and 7 am but she's put her foot down with a firm hand.

Thanks.
It’s a tricky one at the moment as while I have quite favourable off peak times  (5.10am - 3.10pm approx), the tariff is expensive. 
I’m able to heat water at off peak times and run washing machine, hoover etc...

The on demand heating I’m using at the moment is using half off peak and half peak electricity due to it switching mid afternoon.
Over three days and since swapping to convector heaters, I’ve used 28kwh low rate and 17kwh normal rate. 

Cardew

Mickey666 said:

Electric heaters are basically 100% efficient, as in all the electrical energy is turned into heat (assuming no fan).
Oil-filled electric radiators can't change the basic efficiency and if it uses 2kW of electricity then you'll get 2kW of heat from it. 

As Scotty would say "ye canna change the laws of physics Captain"

Can I make a point about a fan and quote someone with possibly even more knowledge about physics than Scotty(albeit Star Trek fans might disagree) namely Albert Einstein.

He famously stated “Energy cannot be created or destroyed, it can only be changed from one form to another.”

So in a room if you have:

1.  a heater using, say, 1kW without a fan,

 2. a fan heater with a 950w element with a 50w fan,

 3. a fan heater with a 800w element with a 200w fan,

 4 a fan heater with a 900w element and a 100w lamp.

5 a 1kw fan

6. 10 humans working out each producing 100w of energy.

Then the same amount of heat will be produced, and if in each case that output is sustained for an hour, 1kWh of heat will be introduced into the room

Mickey666

Interesting examples.
I suppose it depends on whether the energy used by the various fans is ALL turned into heat.  Some of it certainly will be (and the motor will get hot as a result) but what about all the air being moved about?  It takes energy to do the 'work' of moving air and if ALL that energy turns into heat then where does the energy come from to do the work of moving the air?
Similarly with the 100W lamp.  A certain amount of that 100W will be converted into light (the amount being dependent on the lamp efficiency), so surely that amount cannot be converted into heat?
Also, more intuitively, will a 1kW fan really heat up a room as effectively as a 1kW heater?

Talldave

A fan's primary outputs are motion and noise, heat output is minimal.  Taking the above examples to the extreme, a fan heater with a 5w element and a 995w fan would produce a massive gust of air at a temperature indistinguishable from room temperature. 

Cardew

Mickey666 said:

Interesting examples.
I suppose it depends on whether the energy used by the various fans is ALL turned into heat.  Some of it certainly will be (and the motor will get hot as a result) but what about all the air being moved about?  It takes energy to do the 'work' of moving air and if ALL that energy turns into heat then where does the energy come from to do the work of moving the air?
Similarly with the 100W lamp.  A certain amount of that 100W will be converted into light (the amount being dependent on the lamp efficiency), so surely that amount cannot be converted into heat?
Also, more intuitively, will a 1kW fan really heat up a room as effectively as a 1kW heater?

The energy to turn the fan is electricity, but the heat produced by the fan is the friction of the air moving( and the heat of the motor)

There are thousands of websites on this subject, mainly concerned with calculating the heat produced by friction of an object passing through a gas e.g. a plane flying through air or a space capsule on re-entry

Is Your Fan Actually Heating The Air? - Forbes

All light(100%) will be converted into heat when it hits a surface.  IR heaters work on this principle except humans don't see the light.

Sunlight(energy) coming through even a triple glazed window will heat the surface of anything in its path. That is why a glass conservatory can be unbearably hot.

It wasn't my intent to discuss physics, but there are many posts implying a 1kW fan heater produces less heat than, say, an oil filled radiator - because the fan uses x watts - but they both produce the same amount of heat.

 

dosh37

Talldave said:

Taking the above examples to the extreme, a fan heater with a 5w element and a 995w fan would produce a massive gust of air at a temperature indistinguishable from room temperature. 

A politician can also produce a massive gust of air at a temperature indistinguishable from room temperature without any fans.