Are watts not watts?

[K8MHZ]

If an electric heater is rated at 1500 watts and is entirely inside the room it is intended for and is measured to draw the correct current to provide 1500 watts does anything else matter?

I don't see how it is possible for a 500 dollar heater rated a 1500 watts to provide any more heat than a 17 dollar heater rated at 1500 watts.

Am I missing something or are the expensive electric heaters a scam?

FWIW, I do know users of the expensive heaters that claim huge savings on their other heating source, primarily propane.

I am a big fan of the cheap heaters because for a fraction of the initial expense and the same cost to operate, I can pretty much shut the furnace down, even at 20 degrees or less, by just heating the room the T-stat is in.

I wonder if the folks that bought the expensive heaters ever really gave the cheaper ones a chance.

 

[Dennis Alwon]

The cheaper heaters probably won't last as long. Cheaper parts in the cheap heater-- more than likely, but 1500 watts is 1500 watts.

 

[nakulak]

the question is, would the cheaper heater burn your house down quicker than the expensive heater. Or more accurately, would it be more likely that the cheap heater is made so cheaply that it is more likely to burn down your house. In other words, is it worth twenty bucks to buy a heater that has more safety features that would make it less likely to burn down your house ? Buyer beware

 

[winnie]

If your question is: will a cheap 1500W resistance heater heat up a sealed insulated room as well as an expensive 1500W resistance heater, then yes they are equivalent.

You _may_ find differences in the effectiveness of two heaters with respect to putting heat where you want it. The goal is not to heat the room, but instead to make people feel comfortable in that room. If one heater somehow does the job of making people feel comfortable with less actual heat being supplied, then that one will use less electricity. Electric blankets, for example, are a popular way to make do with less actual heat.

Additionally, electricity can power a heat pump which will deliver more watts of heat to the room than electricity consumed, by the mechanism of 'gathering up' heat from elsewhere.

-Jon

 

[chris1971]

Maybe the cheap heater is painted with lead paint from China?

 

[suemarkp]

There seem to be 3 ways you can do electric heat -- the baseboard or portable radiator, the forced air unit (portable or wall), or the directed radiant type (ceiling or portable).

I always thought baseboard seemed cold. It heats the room air near it which eventually heats you. Furnishings (e.g. couches) seem to always block a lot of the output and force it to the ceiling.

The forced type air heats the air and circulate that air better.

The directed radiant types feel nice and warm if they are aimed at you. But the air and some surfaces can still feel cold.

But the BTU/Hr to the room is the same based if heating element wattage is the same. The heat just may not be where you want it.

 

[kbsparky]

The cheaper heaters probably won't last as long. Cheaper parts in the cheap heater-- more than likely, but 1500 watts is 1500 watts.

Even those expensive ones burn out. One of my customers asked me to look at their heater -- had a burned out element. But in defense of the expensive manufacturers, once I gave them the serial number when trying to obtain replacement parts, they informed me it was still under warranty! They sent me the parts free of charge, and I was able to repair the heater easily.

One thing I can say is those heaters are BUILT! 2 outer layers of galvanized steel, and lots and lots of screws hold them together. Easliy disassembled and repaired.

You can sit on one, or use it as a hassock if you wanted to.

I would not pay the hundreds of $$$ they want for one, but to some folks cost is secondary. Easy come, easy go.

 

[Jraef]

The issue is thermal transfer. A cheap heater will give up all of it's heat fast, a better one will give it up slowly. Watts are watts as you say, but heating is BTUs is energy, not power, which is closer to kWh or watts over time. So although if you are standing in front of both heaters when they are on full blast for a few minutes you may not be able to tell the difference, the process of raising the heat in a closed room will be different. Once the room gets up to temp, the cheap heater shuts off and quickly reverts to the ambient temperature. A more expensive heater, such as a ceramic core version or an oil heater, remains warm longer. So as the room walls themselves give up their heat, the better heater is still contributing to the ambient and may not need to come back on as soon, whereas the cheap heater cycles on and off again more often. Even if, in the long run, the kWh ends up being the same, the cheap heater core suffered more on-off cycles than the expensive one, thus having an accelerated demise.

 

[mivey]

I can pretty much shut the furnace down, even at 20 degrees or less, by just heating the room the T-stat is in.

I can shut mine down with the push of a button.

The expensive heaters are pretty and can have higher quality parts. As for the output, BTUs are BTUs but the way they are dispersed can be a deciding factor.

If one part of the room is warmer than the rest, there is a chance that more heat will escape to the outside faster because the delta T is greater on the warmer wall.

 

[chris1971]

Is it 10 watts per square foot when deciding size to install?

 

[Dennis Alwon]

Is it 10 watts per square foot when deciding size to install?

I think that depends on where you are in the country and how well insulated you are. Many factors go into this but I would say that 10 watts/sq.ft in Minnesota may be okay if it is fairly well insulated. I used to use 7watt around here in NC on not so well insulated houses.

 

[gmtt]

jreaf said it all on thermal issues. Couple of more issues are control, safety, mechanical construction etc etc (non-energy related). An expensive heater may have all of these than a cheaper heater. It's like a car with fully loaded vs the same car with strip down version (same power and torque, but....)

 

[mivey]

jreaf said it all on thermal issues.

Hardly. It was a post on the number of on/off cycles due to the release time of thermal energy.

As I stated, another thermal issue is the dispersion of that energy in the room and the effect on heat loss. A simple heat loss formula for the loss through insulation (or a wall) would be:
Heat Loss = Surface Area * Delta T / Insulation R-value

The heat gain of a material is :
Heat Gain = mass * specific heat * temperature change of material

These can be combined to get Newton's Law of Cooling:
Final Temperature = Ambient Temperature + (Starting Delta T)*e^(-k * time)
where k = surface area / (mass * specific heat * Insulation R-value)

So, assume we put the heater next to an outside wall. The exterior wall next to the heater has mass. If more heat from the heater goes to over-heat the wall relative to the rest of the room, more heat will be lost to the outside than if the heat energy were evenly dispersed around the room.

The heater will have better performance if it is able to radiate the heat further into the room. The more expensive unit could put more effort into spreading the heat energy.

That said, I have found a cheap electric heater in the center of the room to be a good value (not so great if you have toddlers). The problem is that it is very hot when you are close to the heater but cool at the room edges because we have no fan.

A ceiling fan will help disperse the heat and equalize the room temperature (the fan might be built in to an expensive unit). The exterior wall will always be a heat sink and will be a cooler zone. This effect can be reduced with a higher R-value for the wall.

 

[awc]

Even those expensive ones burn out. One of my customers asked me to look at their heater -- had a burned out element. But in defense of the expensive manufacturers, once I gave them the serial number when trying to obtain replacement parts, they informed me it was still under warranty! They sent me the parts free of charge, and I was able to repair the heater easily.

One thing I can say is those heaters are BUILT! 2 outer layers of galvanized steel, and lots and lots of screws hold them together. Easliy disassembled and repaired.

You can sit on one, or use it as a hassock if you wanted to.

I would not pay the hundreds of $$$ they want for one, but to some folks cost is secondary. Easy come, easy go.

I think I know which heater you're speaking of and it's much better than the other one advertised. The customer service on the other one is a joke and you can't find replacement parts for it anywhere, not even the manufacturer will supply or give you a source. Most likely because the unit comes from over seas. The unit you speak of is decent and easy to fix, you're right they are built very well..............almost forgot and VERY EXPENSIVE!!

 

[workin4living]

Ok, newbie question here.....................If 1Hp is equal to 746 watts why does some of the info I read from Generator sites show wattages of 1/2hp motors around 1000 watts approx??? I'm confused, what am I missing??

 

[suemarkp]

They have a huge current inrush which the generator needs to accommodate. If you had a 1/2HP generator supplying a 1/2 HP motor, that motor may never start if it is loaded up.

So that generator site is putting in a fudge factor to provide enough headroom to start the motor. But it isn't really that simple. A table saw is much easier to start than a HVAC compressor.

 

[rattus]

Ok, newbie question here.....................If 1Hp is equal to 746 watts why does some of the info I read from Generator sites show wattages of 1/2hp motors around 1000 watts approx??? I'm confused, what am I missing??

You are ignoring efficiency. To produce 1hp of mechanical power, you must input the 746W delivered plus some 250W of losses.