Determining rating needed for oil-filled radiator

[GRC]

Our house is built into the side of a hill, and at ground level to the front we have a downstairs hallway with front door, and access to the garage via an internal door. All other accommodation at one and two floors up. The original builders didn't fit a radiator down there, and for years we've been using a little portable panel heater - coiled radiant wire design, as far as I can tell, rated at 500w. It takes the chill off, but doesn't really warm the place.

We're getting a wall-mounted oil-filled radiator fitted, but trying to judge what rating to get. Want it to give more heat, but not go too high so that we're wasting money on a more expensive one that we don't need.

I'm told that the thermal oil in them makes them more efficient than the equivalent panel heater like ours, but if we go for a 500w oil-filled, will that be noticeably warmer than the current panel heater? Should we go for a 750w or 1kW?

 

[flameport]

I'm told that the thermal oil in them makes them more efficient than the equivalent panel heater like ours,

No.

500W is still 500W.
The difference is that an oil filled one will take a lot longer to heat up, but will remain hot for a while after it's switched off.
Actual heat output is the same.

 

[ericmark]

All resistive heaters have the same efficiency. Using a heat pump, or inferred can change it, but the difference between a panel heater and oil filled radiator is the hysteresis, there needs to be a time between heater switching on/off/on etc to maintain the temperature as other wise the contacts would wear out, and the heat held in the oil bridges the gap, so heat is being delivered all the time, idea is the heat has natural thermals within the room. from your description not sure that will happen, with inferred it heats the person direct not the air, but that means it can't be thermostatic controlled, only way to control inferred is to have multiple bars so you can select how many are used.

Some panel heaters are part inferred but that means can't be switched off, or feels cold straight away.

 

[GRC]

What is "inferred" in this context?

 

[pcaouolte]

What is "inferred" in this context?

Probably "infrared".

 

[cjcoffin]

If 500W is not enough then fit 1kW, but make sure you get one with thermostatic control or fit a wall-mounted thermostat, that way you can control it to your liking and not use an unnecessary amount of power. As others have said, oil-filled will have a longer time constant which may help.

 

[Mottie]

Go high, you can always turn it down. Go low and if it ain’t enough, it ain’t enough!

 

[Ivor Windybottom]

The electric heating industry is full of bull and waffle making all kinds of snake-oil claims. Oil isn't any more or less efficient than anything else at transferring heat, it just moves heat from the element to the air like water, metal or any other material. Whatever it's made from, 1W of electricity will become 1W of heat. If any salesman, brochure or website makes any claims involving "efficiency" for an electric heater then they're con artists or at best simply don't understand basic physics.

All that aside, oil filled radiators are OK. They don't clog with dust as a fan heater does, and don't produce burning smells. But you will never get their rated power out of them. They all have two thermostats - one that monitors the room temperature, another that monitors its internal temperature to prevent overheating. Usually the overheat thermostat keeps the element mostly off, because the puny size of the things usually means that they just don't transfer the heat to the air as quickly as the element adds more heat. You may well find that a "2000W" heater is more likely a 500W heater as it spends three quarters of its time off to prevent overheating.

Ours are all 2000W (2kW). They have two switches, each is for one 1kW element. There's absolutely no point in switching both on, we just use one. This way it spends about half of the time on at 1kW, instead of a quarter of the time at 2kW. The end result is the same amount of heat and power either way, using both elements just means it's on for less time.

Look at the size of a 2000W radiator for a central heating system - they're huge. 2000W oil filled radiators are usually a fraction of this size, so they are just not capable of providing 2000W of heat into the air of the room.

To judge how effective it will be, you need to look at its surface area and airflow, not the element rating.

 

[Ivor Windybottom]

Also... any electric heater will cost around 3x more than gas heating. As you already have a radiator system you may save in the long term by plumbing a radiator in and heating it with the existing system. While you're at it, it would be a good place to add a drain-off valve so the system can be drained out via a hosepipe through the door when servicing or repairs are needed in future.