Portable heaters & thermostats

chemicalfan

This is a simple question, but one I'd like an answer too, based on experiences or maths, rather than "hunches"!

Say you've got a 2kW oil filled radiator, with a thermostat, and 3 heat settings. Say you set the thermostat halfway. In terms of electricity consumption, does it matter what heat setting you use? 800W, 1200W, or the full 2000W? This question also works with convector heaters (and fan heaters, I guess), anything with multiple heat settings and a thermostat.

HappyMJ

It doesn't matter...set it to the highest setting and you will get heat quickly then it will cycle on/off to maintain the room temperature. Once it's done that then manually turn it down to 800W and the heater won't cycle on/off as much making you feel more comfortable as the temperature swing in the room won't be so great. If the room is cooling despite the heat being set at 800W then turn it up to 1200W and see how that goes.

chemicalfan

Well, the thermostat sets the threshold at which the heater turns off - setting it higher won't make it heat up any quicker (it heats up according to the heat setting, as far as I know). Something I have to explain to my OH when she's using the oven! lol

In my head, applying logic, once it's at the threshold and cooling, the 2kW setting should mean get the oil back up to temperature quicker than the 800W setting. Assuming that the 800W setting has the capability to get to threshold (otherwise this is a pointless question!), it will get there but take longer. Logically, the electricity used should be the same - 2000W x 5 minutes = 800W x 12.5 minutes. It's the heat losses and other bits I'm not sure about!

macman

No 'hunch' is required. It takes a fixed xkWh's of heat energy to raise the room temp from A degrees to B degrees, regardless of the rating or power settiing of the heater you use. If you want the room to heat quickly, use the highest power setting. All that changes is the rate of delivery.
Of course, using the lowest power setting will be slightly less effective, as the longer heating time required will result in more heat loss from the room, but that's fairly marginal in this context.

chemicalfan

That's what I thought. In terms of electricity consumption, it won't make a difference (unless 800W costs more due to heat losses while heating up/cycling). In this example, it's a cold room, with an uninsulated concrete floor (just thin carpet).

I guess 2kW is the only setting that matters, and it's all about the thermostat. Thanks for the replies all

andyrpsmith

A good way to determine how the heater is reacting is to connect an energy monitor and play around with the thermostat setting and heating elements.

I recently did this with my Delonghi Rapido 3KW oil filled heater.

It has a 500W, 1.5 and 1.0KW setting. The 500W is a rapid warm up element that is not controlled by the thermostat but the switch for this element is part of the intelligent heat system that allows the heater to individually control the 1.0 and 1.5 elements with the thermostat.

I usually set the thermostat to 3 (I think the range is 0-6) and all the elements on, once the thermostat trips and starts cycling the measured output is 12p/hour (around 1KW as my tariff is 11.34p). If I want the room a tad warmer and set the thermostat to 4 the output doubles to 24p or 2KW.

Shows how easy it is to increase your spend with a small change to the thermostat.

macman

But it doesn't cost you any more to heat the room to 4 whether you use one element or another, or both. All that changes is the rate of heat delivery.
When on a 2KW setting, the running cost doubles, but it produces heat at twice the rate as when on 1kW, so you'll still use the same amount of power to heat to a temp setting of 4.

andyrpsmith

macman wrote: »

But it doesn't cost you any more to heat the room to 4 whether you use one element or another, or both. All that changes is the rate of heat delivery.
When on a 2KW setting, the running cost doubles, but it produces heatt at twice the rate as when on 1kW, so you'll still use the same amount of power to heat to a temp setting of 4.

Not sure why you are telling me this, the point of my post is to determine how your heater behaves when you change the thermostat setting and how it may affect the cost. Pretty obvious that running 2KW will cost twice as much as 1 KW.

HappyMJ

andyrpsmith wrote: »

Not sure why you are telling me this, the point of my post is to determine how your heater behaves when you change the thermostat setting and how it may affect the cost. Pretty obvious that running 2KW will cost twice as much as 1 KW.

But the thermostat will turn a 2kW heater off half the time. A 1kW heater would stay on all the time. Usage after one hour using either setting 1kWh. It's not as obvious as you think. What about a combi gas boiler that outputs 32kW does that use more than a 12kW conventional boiler? No they use the same. Assuming the heat loss of the house is less than 12kW then the usage by either boiler will end up being more or less the same.

Nada666

Although the arithmetic unchangeable laws of physics theoretically say one thing about an ideal room the practical comfort in situ may differ.

This is random speculation (exactly what the OP doesn't want respondents to do ) but a lower setting may be more suited if you are talking about one or two persons sitting together. My theory is:

if you slap it on at 3kW then it will be too hot to have near you - you will rely on the thermostatic medium of the whole room to keep comfortable. If it is on at 500W or 1kW then you may be able to sit comfortably in its direct path and have the thermostat set at a much lower number.

grahamc2003

chemicalfan wrote: »

This is a simple question, but one I'd like an answer too, based on experiences or maths, rather than "hunches"!

Say you've got a 2kW oil filled radiator, with a thermostat, and 3 heat settings. Say you set the thermostat halfway. In terms of electricity consumption, does it matter what heat setting you use? 800W, 1200W, or the full 2000W? This question also works with convector heaters (and fan heaters, I guess), anything with multiple heat settings and a thermostat.

You'll use the same energy to get it to click off. You need a certain amount of energy to raise the temperature to the set temperature. Say you need 2kWh. This would be supplied after 1 hour at 2kw power setting, 2 hours at 1kW or 4 hours at 500W.

Power (kW) is just the rate of change of energy (kWh).

(That's a first cut explanation, there are other effects affecting the amount of energy used, but they are negligible to the question posed).