Benefits of oil-filled electric radiators? And which portable heater type is most efficient really? 1

[LMF5000]

I've looked at and operated oil-filled electric radiator-style heaters (image shows an example) and I'm wondering what the benefits are for manufacturers to go to the trouble and expense of increasing their thermal inertia by filling them with mineral oil instead of heating the fins directly. Surely if they consume 1kWh from the plug, they're going to put 1kWh of heat into the room, same as any other type of electric heater?

A second follow-up question - which is the most efficient heater type in real life? I'm not talking energy efficiency (we all know all electric heaters are 100% efficient at turning electricity to heat; I'm ignoring heat pumps). What I mean is, which kind of heater will make an occupant in a room feel "comfortable" with the least amount of energy expenditure? Or, in terms of an experiment, if you put someone in a room with a heater and give him access to the switch/thermostat, and measure how much energy he consumes over an 8-hour day to keep it cosy (while controlling the external environment for consistency), which heater type would come out on top?

Anecdotally, I was quite impressed with halogen. A mere 400 watt tube caused a lot of very obvious heating, and they handle draughts well (like an open-plan office). I found fan heaters good at heating up the air in the room, but the power consumption is significant (2000W), they're noisy, and the temperature and noise fluctuations from the cycling of the thermostat are annoying. I have no experience of quartz, ceramic, mica, passive convection, panel heaters or any other kind.

Currently using an oil-filled radiator and it seems to be a good compromise. Heats up without the noise of fans nor the glare of halogen. I also have a heat-pump split-type wall-mounted inverter air conditioner in the room. Quick comparison test showed that for a 1°C temperature rise in the same room, the AC only consumed 0.8kWh while the oil-filled radiator consumed 1.2kWh (so a 70% savings going with the AC) - but it's not a fair comparison because the AC cost €700 and these heaters are only €20-€70. And the rooms I'm looking to heat won't have the possibility of installing AC units.

 

[EnergyProfessional]

Any electric resistance heater will have the same 100% efficiency. The difference is if they heat he air, or radiate or both. the halogen bulb or a regular fan-heater will heat instantly and will stop heating nearly instantly after the thermostat switches off. That oil heater will have smoother curve and will put out heat slower initially, but after the thermostat turns off, will continue to heat and slowly degrade heat output. and it also doesn't make noise, like a fan heater and doesn't move air around, which creates dis-comfort.

Which one to choose depends on the application. A living room may be better served by a oil heater, a garage where you only want to heat the person for a few minutes may be better served by a radiant heater (like the halogen). But for all it means, 1 kWh electricity in = 1 kWh heat out.

 

[Compositepro]

First, there is no such thing as thermal inertia. It is called heat capacity. The rest of the observations in your post are pretty astute.

As to what is the best heater, it depends on the specific environmental conditions, how one is dressed, and personal preferences. For heaters that operate on a 120vac, 15 amp circuit, 1500 watts is about the maximum available power. The oil-filled radiator is silent and can provide 1500 watts without any exposed high temperature parts, so it is very safe around children, pets, and generally clueless people. It radiates heat in all directions, but cannot overheat curtains and the like. Convection takes cold air off the floor and warm (but not hot) air rises. Hot air tends to sit at the ceiling where it does not contribute much to comfort and maximizes heat losses. The heat capacity of the oil lessens the comfort changes between being on or off, but it does increase the time before you start to feel any heat.

In large spaces where it is not practical to warm the whole space, radiant heat is usually the best, or forced warm air directed at the place to warm.

 

[LMF5000]

I'm in Malta so the electrical supply is 230V @ 13A (circa 3000W maximum). Though usually they keep heaters to 2000-2500W max.

Interestingly, modern oil heaters are much, much smaller than the ones from 10-20 years ago despite having the same power and the same general appearance. On this one, I've measured a surface temperature of 130°C on the fins with an infrared thermometer - it gets much hotter than the heaters of old, obviously due to having a smaller surface area in contact with the air. So it does get hot enough to burn you at high power, but I know what you mean compared to the searing heat of a quartz tube or something.

Another observation I made with my wattmeter is that leaving it at the high setting (2000W), after about 10 minutes the unit hits the thermal limit (about 170°C on the surface of the lower part where the coils are embedded) and the safety thermostat cuts out the high power coil, leaving only the low power coil (800W) powered. So despite being labelled as a 2000W unit, you can only get 800W of output steady-state (unless you have a very cold room I suppose).

 

[EnergyProfessional]

I'm sure it has a safe built-in oil temperature to not exceed. You don't want boiling oil or just too expanded oil that bursts the vessel.

The surface area size for a given wattage may be a function of cost. A cheap heater wills safe material and be smaller. the limitation is higher surface temp (safety!) and limited heating capacity in warmer rooms. If you use it in a cold room (garage), it may not get too hot and keep the 2md stage on (I assume it has 2 stages, 800W, and 1200 W based on your observation). I guess it is like a 800w heater, but with an initial 2kW boost to heat up the oil quickly.

Your 230V is nominal, based on the old 220V. And for long term uses you only can count 80% (at least in US electrical code - but electricity is the same all over). So you never see a heater that will use 100% of what you theoretically could use on an outlet. And if you had 3000w heating element, the heater would need to be much larger and your meter will be spinning. Better insulate your house if you need more than 2000W. Or have permanently installed heaters. Those plug-in heaters are not for unobserved operation (like you leave the house, it could be unsafe and start a fire). They are just for heating when the person needing heat is there. At least in theory. Malta doesn't get that cold, get a sweater

 

[MintJulep]

"Space Heater Nonsense"

https://www.youtube.com/watch?v=V-jmSjy2ArM

In general, this guy's videos are fun to watch.

 

[EnergyProfessional]

MintJulep: timely posting. I had just came across his channel a few weeks ago. He has a very good mix of being educational AND funny.

 

[3DDave]

His toaster video is hilarious and educational.

https://www.youtube.com/watch?v=1OfxlSG6q5Y

Ha also did a series on kerosene lamps.

 

[LMF5000]

Watched that video already. In fact I've been a subscriber of Technology Connections for years, mostly for his videos about 1990s hifi equipment

 

[LittleInch]

The benefits for the manufacturer is that they are selling something that people want to buy as cheapy as they can.

Pressed steel bodies cost very little. This allows a single rod element which is nice and cheap and radiates heat nicely.

You can get similar cheap convection heaters which have wire coils hidden inside a metal box.

Your second part is more personal so no one answer. However I think most people would now say they prefer a stable air temperature of between 20 - 22C.

The best way to deliver this is in slow but regular input of heat into a room. If you look at the UK, most heated homes use a water filled radiator system which sits at between 60-80C and provides a steady supply of warm air at probably about 30C into the room creating a circulating air mass. Nice "background" heat. Oil filled radiators do the same sor tof thing but it is interesting that surface temps have increased as manufacturers cut costs to the bone. So buying a higher powered but smaller oil filled radiator won't supply what is says is max power.

I used to heat a small outside room which was converted to an office with such a heater. First thing in the morning I used to position a fan behind the radiator and blow air through it and also at times during the day to heat my feet up (No floor insulation). So best of both worlds....

Heat pumps down to a certain temperature have a decent COP of around 2 usually so use that in preference wherever you can.

energy P - My guess is that Malta is actually 240V as an ex British Island, but even 220 is so much better than the weedy 110/120V in use in the US... . But your points are well made.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EnergyProfessional]

If you use a convector or the oil heater, place it in a room under the window (like you would do with a hydronic or steam radiator). that way the warm air rises to the ceiling and and falls back at the opposite wall (which most likely is an interior wall). that air will flow back to the radiator and goes along your fee. that air still will be somewhat war. If you do it the opposite (radiator on inside wall), the air that goes back by your feet is much colder since it went by the cold window before falling down.

Doesn't change the energy balance or efficiency, but increases comfort and maybe you could lower the thermostat by 1°F, which would save energy. But main reason is comfort, a single temperature point alone doesn't show you how comfortable people will be. and comfort the the whole reason to have shelter and heating to begin with.

 

[Stick.]

Matthias Wandel has a few good videos on space heaters, including this one where he discusses the reduced steady state heat output of some oil filled space heaters: 600 watt heaters pretending to be 1500 watts. There's also this one where he does some experiments to test how well an infrared heater works in practice: Infrared vs space heater: How warm does it feel. Both of them pretty much align with your initial impressions, but they're definitely an interesting watch.

 

[LMF5000]

Thanks!

Mine has the same issue. It has two elements, one 800W and one 1200W. In heat setting 3 it turns on both elements for 2000W. When it hits the upper thermal limit (independent of the thermostat), the large heating element turns off. So in setting 1 it continues to deliver 800W until the thermostat cuts out (or runs continuously if the thermostat setting is high enough). In heat setting 2, it runs at 1200W until the thermal cutout, then draws 0W until it cools off (remember only the 1200W element gets affected by the overheat cutoff). In heat setting 3 it runs at 2000W until the cutoff then falls to 800W after that.

I found it very interesting that after reaching the thermal overheat cutoff you actually get more power in the low heat setting (setting 1) than the medium (setting 2) because of the way the overheat cutoff switch turns off the 1200W element only.

It takes about 10 minutes at full power to reach overheat cutoff. Thereafter, 800W is enough to keep it from ever cooling down enough to un-trigger the overheat cutoff.

 

[moon161]

You could cool it with a fan and extract more heat from it to heat a room faster.

 

[LittleInch]

That's what I used to do with mine and it works a treat.

Interesting to know that the vendors seem to have pushed the envelope too small to create cheaper heaters which don't really do what it says on the tin.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EnergyProfessional]

moon161: with a fan you could make it even smaller. Maybe don't even use oil and make the heating element more like a coiled wire. Maybe directly expose that wire to the airstream from the fan. That then would be an even cheaper oil-radiator

From what I learned here, these small (undersized?) oil radiators basically use the full power only as a booster for the initial heat-up and/or for use in a very cold room (more heat transfer in cold air). In my young days those oil-radiators were large. In the modern time they got smaller and I wondered how they managed to do that. Now I know why.

 

[LMF5000]

And they were slightly sneaky about it - the appearance didn't change. You've still got a stamped structure with a couple of stamped ribs, and welded circular joints top and bottom. Looking at pictures when you buy online, there's no way to visually realize how much the size has changed - you'd have to look at the numerical dimensions and realize. I have some old radiators from many decades ago, when 2000W meant continuous power, and they're about 4x the volume of my new little "2000W" (actually 800W continuous) oil-filled heater.

EnergyProfessional - that's kinda what inspired my question. I've used fan heaters as well. They do a better job of heating the room fast, and they're the cheapest and smallest heater types for the power. Their disadvantages are that they're noisy, and that the room gets cold when the thermostat cycles off. So the quality of the heat isn't as good as an oil-filled radiator. Perhaps the best of both worlds would be to put a box fan in front of my little oil-filled radiator so it can run at full power continuously. Or maybe I should have spent more money on a dimensionally larger oil-filled radiator that can dissipate more power passively (but this isn't an issue in my case because actually I don't need more power for the small rooms I'm trying to heat with it).

 

[EnergyProfessional]

If you combine the oil heater and a fan, you kind of get the worst of both worlds. An older-style (larger surface area) type would be best. The old-style are really nice since they avoid the hot-cold-hot-cold cycles, don't move air (moving air cools warm bodies, like humans), don't make noise. They also have a good ratio of radiant heat and convection heat. The only inherent drawback is longer initial heat-up due to thermal mass. but that is only an issue initially. the problem we have here, is due to bad execution and not inherent.

I never looked at dimensions to see that newer ones are smaller. I just go by the smaller number of ribs. it looks like the first vertical piece that contains the controls is the same size and the ribs are about the same for new and old types. The real difference is, the older style used maybe 7 ribs, the newer style uses 3 or so. And that was very obvious when I saw them in stores (with no intent of buying).

 

[LMF5000]

Aha! See, that's what I meant about them being sneaky. The number of fins (ribs) is about the same, give or take a few. But they made the entire heater smaller, including the front panel. Since everything is scaled down on the heater and the pictures only show them in rooms without a proper size reference (like a person's hand, or an electrical socket, or something else of known size), that's what gives the illusion that they're the same size as old ones. My small one is 0.75x the height, 0.75x the depth, and about half the width of the old large radiators.

 

[LittleInch]

"Worst of both worlds"? Hmmm - you can get a pretty quiet fan nowadays especially on setting 1 - It heats the room up faster an then you just let the normal oil heater work to maintain a good background temperature.

I remember an old oil heater and it was a monster compared to the newer version, but guess it worked harder for longer...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.