[Quinny]

We have a point application for electric heaters and are trying to decide which to go for?

We actually already own some old electric wall heaters, but my wife is saying they are not as efficient as the 'new' ones and furthermore the new more 'expensive' ones are 'more efficient'.

I always thought that electric in and heat out is constant, so don't get how the 'efficiency' rating works. It's not just 'controllability' factor or the potential to use cheap night time electric.

I've googled to try and work out how they grade these devices, but can't seem to find how they do/justify it.

Anyone understand?

[KaiserJeep]

First of all, define what it is that you are trying to heat. What I mean by that is that submersible aquarium heaters and electric water heaters are also "electric heaters". Resistive elements embedded in concrete under a tiled bathroom floor are "electric heaters". So tell us what you are trying to heat and what sources of heat are available.

What you said is accurate in a very narrow sense. If you are actually talking about heating air and then blowing the heated air into an enclosed space, and the electricity supply is the only source of heat, then the design of the heater is not important.

However, if one is permitted to pump heat from groundwater or even cold outside air into your heated space, then "ductless mini-split" heat pumps can be up to about 40% more efficient than pure electric resistance heating, with the exact value depending upon several variables such as the air temperature outside, the air temperature inside, and the time available to heat the space. When you can pump heat from cold ground water instead of outside air, the efficiency can be 50+% better than electric resistance heating.

If you can put solar thermal collectors on your roof, use them to heat a large tank of water, and then use an electric heat pump to warm your space, you could see efficiencies that exceed 100% better than resistance heat - and if you can add solar photovoltaic panels, you can have absolutely free heat, after the system pays for itself.

You could also add insulation and heat recovery ventilation to your living spaces and avoid heat loss and completely avoid the requirement for space heating. As they say, "insulation is fuel #1".

Lastly, and with complete sincerity, you could avoid arguing with your wife and simply give her what she wants. This may be the most efficient path to marital bliss, even though there is no official Law of Thermodynamics that supports this.

[Quinny]

Thanks KJ - understand heat pumps, but in totally different league cost wise.

We have a couple of rooms that the heat from the wood fire doesn't 'reach' properly.

Looking at using cheap electric heater for short period to avoid damp.

Comparing ceramic/mica/fan/convection and being told modern ones are more efficient. I've got 3 old ones upstairs that cost nothing and don't understand why they might be less 'efficient'!

[dinopello]

I think the main difference with electric space heaters is whether they are convective hot air blowers or use an oil filled heat resevoir for a radiator. The latter might be more efficient in some sense but it depends on your application as to which is the most appropriate.

[KaiserJeep]

It is completely true that all electric resistance heaters are equal in terms of efficiency, which is fairly low. It does not matter whether they are filled with oil or ceramic or mica disks. If you just want to heat air, then choose a model that has both a blower and heating elements, and locate the heaters where needed.

Understand that heat can also be transferred via conduction and radiation. Do not use heaters that lack forced air blowers for the application you describe. Also, such electric heaters tend to be cheaply constructed, so after the heater has been in operation feel the plug and the entire length of the electric cord for hot spots - and repair/replace it as necessary.

Check the safety features. UL requires electric heaters to shut off when tipped over. Test it.

It does not make financial sense to use such heat for extended periods every year. Consider running small diameter insulated ducts from the ceiling above your wood stove into each of these rooms, through an attic space if possible. A small 3" diameter fan such as a computer fan is often sufficient to warm an entire room through forced air circulation. Leave the doors open or at least have a 1" gap under each interior door for cold air return.

[vtsnowedin]

Consider running small diameter insulated ducts from the ceiling above your wood stove into each of these rooms, through an attic space if possible. A small 3" diameter fan such as a computer fan is often sufficient to warm an entire room through forced air circulation. Leave the doors open or at least have a 1" gap under each interior door for cold air return.

I would not run a duct through the attic. You would be above most of you insulation and then have to try to push the heat back down at the end meaning that without a fan in the duct it would not work at all.
Small fans at the top of doors do work pretty well but I don't like the buzz and being tall have to be careful not to bump them. Instead I use two foot floor fans set on low sucking the cold air out of the room I want warmer. The stove heated air at the ceiling comes through the top of the open doorway to replace what the fan removes.
Gravity is your friend, learn to work with it not against it. I once had an argument with two engineers that insisted on using a floor fan to blow hot stove heated air into our office space. It wasn't working of course and even after I cut thin strips of paper and taped them to the door header to show them the air moved only when the fan was turned around to blow the cold air out instead of in they would turn the fan around their way whenever we technicians in the room were away.

[Pops]

Electric resistance converts almost 100% of the electricity into heat, and they can only pull 15amps (if you are talking about plug in heaters) so the most "efficient" heater is the cheapest one. Those cabinet looking things that are in Parade magazine for several hundred dollars are a huge rip off. The old house we just bought had an oil heater so we bought a couple of "milkhouse" heaters for $15 at Lowes, they work just fine, a little radiant and a little fan to stir the air up.

There are mini split heat pumps made to hang on the wall in just a room or two but I've never used one....
http://www.homedepot.com/b/Heating-Vent ... 5yc1vZc4m1

[Newfie]

West Marine sells a small electric heater with a fan and thermostat that will go as low as 40°F. That lets you keep above freezing, but the you can turn it up when you want some " warm". Other than the very low thermostat setting, nothing special. They also have a fan setting. Then again, maybe a fan is all you need.

http://www.westmarine.com/buy/west-mari ... AiVY8P8HAQ

[GHung]

Pops is correct. Electric resistance heaters convert virtually all of their electrical energy to heat (near 100% efficient in that respect). How that heat gets distributed is a different matter. Adding an electric fan will reduce efficiency a bit in that some of the electrical energy goes to mechanical energy, but may be more affective at heating the space.

[Numbersman]

Yes, all electric "strip heat", (not heat pumps) including ceramic, oil filled, radiant, convective, etc are identically efficient in terms of heat output. However, here are a few things to consider:

I just purchased an oil filled radiant electro heater at Walmart and chose this $40 model over some $15 options because I like the fact it is silent and heats in 360 degrees. Also, II have less heat loss to the outdoors using radiant heat than forced air because the forced air is magnifying the heat exchange from the walls and windows. So I am getting better efficiency than I would with forced air. IE, blowing air on the walls and windows (even slowly) is accelerating your heat loss in the room.

Electric strip in the wall (baseboard heating) probably has more loss through the wall and air currents against will than the same kWh applied interior to the room (rising air on the wall plus losses through the back of the heater).

Couple of other points: Ground or water sourced heat pumps can be 300 to 400 percent more efficient than "strip heat". Air source is good in moderate climates. Thermal mass in front of a south facing window is quick and cheap as well.

Best advice so far: if your wife wants $40 in new heaters, get them!

[Peak_Yeast]

GHung: The energy used for the ventilator is also converted into heat inside the motor, friction against air molecules and so forth. It is correct that the heat loss is quicker with ventilators - but as i write below - it has its advantages.

But I would say its a good idea to have ventilator on the heater otherwise you will get cold corners where moisture might condensate and cause mold. Or under/behind furniture. Moving the air is important.

There can be a "subjective" difference between the different kinds of simple resistive heating elements.
What i mean is that for example some are made as a big plate that radiates the heat which can make the place feel warmer than it actually is.

According to some people electrical floor heating is the least efficient - I am not sure about that. But i can see that the rules concerning floor heating requires 25% extra insulation in the floor here in Denmark.

I would choose the simplest cheapest ventilator heater that can be set at 5-7 dgr. celsius - to keep the rooms mold free.

[GHung]

Yeah, Peak-Y, there was a time I did the math on this sort of thing; had to account for every milliwatt to make the grade. Your basic electric room heater is essetially 100% efficient beyond the plug.

Re: moving air; all of our living spaces have efficient ceiling fans on timers (we never installed the forced air ventalation, except for the duct work. Maybe someday.)

[Keith_McClary]

Small fans at the top of doors do work pretty well but I don't like the buzz and being tall have to be careful not to bump them. Instead I use two foot floor fans set on low sucking the cold air out of the room I want warmer. The stove heated air at the ceiling comes through the top of the open doorway to replace what the fan removes.
Gravity is your friend, learn to work with it not against it.

This should work well if it is upstairs rooms and the fan is blowing towards an open stairwell. Let us know what works, Quinny. Also, how are you at making holes in walls? :

http://www.woodheat.org/move-heat-around.html

[Paulo1]

Quinny,

We heat entirely with wood here on the relatively mild BC coast. However, once in awhile we get some real cold outflows from the interior where the normal +7C day may drop down to -10 C nights and 0 for daytime highs. This happens maybe 2X per year and might last for 2-3 days. I bought a little heater from Canadian Tire that looks like a mini woodstove. It has phony flames that flicker and a small fan. I think I paid $50 for it. Anyway, it's a little nicer than a simple heater and as it is in the back bedroom it doesn't look tacky like it would in a front room. We run it when we want to read in bed for a bit or have a coffee in bed and watch the 'mountain' wake up.

[vtsnowedin]

As shown it will work fine with the door open but stratify and stagnate with the door closed. A grated hole through the wall at floor level with or without a fan in it would work with the transom vent all the time. One other thing: A stove in a kitchen as shown has a six or eight inch stove pipe venting out. There has to be an equal cross section of air opening letting in replacement air. In a tight house you might need to duct in outside air for the stove to breath so it doesn't have to steal the air it has heated for you.
Older houses have enough leaks around windows and doors that there is seldom if ever a problem with this.
My own house has no tightness problems. The large wood furnace in the basement pulls air from around my homemade cellar door and across the floor to the intake drafts. The heated air coming out of the furnace is free to spread over the basement ceiling joists and heat all of the main floor. It also can rise through a two by one foot grate into the dinning room and up through the stairwell which has no door at the top of it and through openings in the stair treads up through the second flight of stairs to the second floor hall. Floor grates around the perimeter walls of the first floor let cold air return down to the cellar to circulate back to the furnace.
I used a fan awhile the morning to change the air in the living room and get it up to where "She" likes it. As it was about fifteen below this morning and just ten above now I didn't think that too unreasonable.

[Pops]

There can be a "subjective" difference between the different kinds of simple resistive heating elements.
What i mean is that for example some are made as a big plate that radiates the heat which can make the place feel warmer than it actually is.

According to some people electrical floor heating is the least efficient - I am not sure about that. But i can see that the rules concerning floor heating requires 25% extra insulation in the floor here in Denmark.

Radiant heat - to be obvious - heats things via radiation (like sunshine) rather than via convection (hot air). So if you sit in front of a radiant heater (the oil filled electric, the wood stove, the sunny window) it is you that heats up, not the air around you. This is what makes radiant floors so comfortable, the floor of course is warm to the touch but it radiates heat to everything in the room, everything you touch is warm, and it does it without overheating the air. The best part is, instead of the heated air rising and pooling at the ceiling where it is basically wasted, near the floor is the warmest. Your toes are toasty while up at head-height the temperature is mild.

The same of course is true of a radiant space heater, like all "light", heat waves decline in strength at the square of distance (or some such nonesense) which is why you "huddle around the fire."

I built a house in the '80's with hydronic in floor heat, plastic pipe embedded in lightweight concrete on a wood floor with ceramic tile finish. It was the best heat I've ever had and I eventually installed it under the carpeted areas (no concrete) as well. I insulated the floor with batts, foil faced, face up.

Insulating floors is important but almost impossible to do right with fiberglass, I'm sure those batts I installed in the '80s are on the ground by now, those that aren't are sagging and filled with mouse poop. To be effective, the insulation needs to be tight against the vapor barrier and not compressed, pretty hard if not impossible to do upside down with speedwires.

I have an old house built over several decades, floor joists go from 2x4 @ 24" O/C to 2x6 on 16". The hot decorator item today is old wood floors and we definitely got 'em! Only part is t&g so at night if I leave the basment lights on it's like walking on stars, LOL.

I think about the best thing for me to do, expensive, but not as much as spray foam (which has to come in from long distance here) is to put up rigid foam panels between the joists. Thermax is R-10 for 1-1/2", fire rated, foil faced. Two layers (R-19 is code now) it is about $3 sq ft tho ... OTOH a new floor starts at $5 s/f.

[Quinny]

Thanks for all the replies which confirm my original thoughts. Have replied before, but it got lost 'somewhere'.

Short term we are using convection/fan heaters with a timer. Cost very little, we had them anyway, but when bought from car boot were only about €5 each.

We are also hoping to source some cheap storage heaters. The night rate here in France is cheap and installation pretty easy. We will time these to only use economy rate to avoid the rooms getting too cold and damp.

[GHung]

Pouring a section of our radiant/hydronic floor.



Three layers of foam board (~R-7.5) below 5 inch slab; ten zones (some rarely get used due to plenty of passive solar). We keep the bathroom floors nice and warm in winter; bedrooms, not so much except during very cold spells. My thinking at the time was that there are numerous ways to heat and store water. Anyway, we love the radiant floors, and we can move/store heat as needed. On days like today, the solar water heater will begin dumping surplus heat into the floor around 2-3 PM. The woodstove heats water in the the same 1600 liter water tank as well.

[Longtimber]

I like this one. Small, Oil filled, Timer & ThermoStat. Search amazon for DeLonghi TRN0812T

[Pops]

Pouring a section of our radiant/hydronic floor.

That's cool Ghung.

Somehow I always had the opinion that slabs are less good than framed floors over a basement/crawlspace - I guess just because they are the traditional method. But after half a dozen houses with rotten bathroom floors, crappy insulation, termite and water damage I've changed my mind.