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Would placing an electric heater in an unused brick fireplace be efficient?

 
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I haven’t read the thread (at least recently), but this seems a good place to ask a question;

Would placing a heater, ( a hot water radiator or electric fireplace) in an unused brick fireplace be an efficient source of heat.

This is in an old double wythe brick-walled unheated zone 5a structure. We are designing a system of radiators and a hot water heating plant to replace electric space heaters that are used in the shoulder seasons. The structure is winterized and closed during the winter and we want to make it year-round residence. The center of the house is held up by a massive brick pier on which a double fireplace faces out on two first floor rooms. The chimney originally also had four wood/coal stoves feeding into it. A major fire that destroyed the roof occurred sometime about 100 years ago and the fireplaces were sealed and a kerosine heater (long gone) was placed in the kitchen. The chimney is in poor repair above the first floor and is home to a flock of chimney swifts each year

For the sake of this question; We will not be using the chimney for wood fires. My thinking is placing a heat source in the fireplace(s) would be an efficient use of electric heat in that the mass of bricks surrounding the source of heat would retain heat and release it back into the space with very little escaping up the chimney which we would insulate above the flue.

Radiators on exterior walls or under windows work well in keeping a space comfortable, but in many structures a good bit of the heat radiates through the wall or windows (not to mention actual air leaks). Having a 1,500 watt ceramic electric fireplace in an central brick fireplace might be just the thing (and has the advantage of being a diy job).

A related question is would the placement of a hot water radiator in the fireplace be an even better idea? We are designing a hot water system already and certainly would be more economical $$ wise than electric.
 
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Short answer, not the way you probably mean it.


James Whitelaw wrote:I haven’t read the thread (at least recently), but this seems a good place to ask a question;

Would placing a heater, ( a hot water radiator or electric fireplace) in an unused brick fireplace be an efficient source of heat.

This is in an old double wythe brick-walled unheated zone 5a structure. We are designing a system of radiators and a hot water heating plant to replace electric space heaters that are used in the shoulder seasons. The structure is winterized and closed during the winter and we want to make it year-round residence. The center of the house is held up by a massive brick pier on which a double fireplace faces out on two first floor rooms. The chimney originally also had four wood/coal stoves feeding into it. A major fire that destroyed the roof occurred sometime about 100 years ago and the fireplaces were sealed and a kerosine heater (long gone) was placed in the kitchen. The chimney is in poor repair above the first floor and is home to a flock of chimney swifts each year

For the sake of this question; We will not be using the chimney for wood fires. My thinking is placing a heat source in the fireplace(s) would be an efficient use of electric heat in that the mass of bricks surrounding the source of heat would retain heat and release it back into the space with very little escaping up the chimney which we would insulate above the flue.

Radiators on exterior walls or under windows work well in keeping a space comfortable, but in many structures a good bit of the heat radiates through the wall or windows (not to mention actual air leaks). Having a 1,500 watt ceramic electric fireplace in an central brick fireplace might be just the thing (and has the advantage of being a diy job).

A related question is would the placement of a hot water radiator in the fireplace be an even better idea? We are designing a hot water system already and certainly would be more economical $$ wise than electric.



Electric heat is "efficient" from an engineering perspective, but additional heat mass would serve no noticeable gains, except perhaps during a power outage. The heat output of an electric heater is, for all effects, continuous; so there's no surge of heat to store, unlike with a wood fire.

Likewise, heat output from a hot water radiator is pretty close to continuous if designed correctly, and the water is the heat mass; but putting either type of heater inside your existing fireplace would be a good use of floor space.
 
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Hi James,

This is a tricky question and largely revolves around how we define efficiency.  If we are defining efficiency in terms of electrical power in converted to thermal power out, then I would think that the electric heater is pretty efficient.  

But I am not so certain that having extra mass would add any efficiency and might actually reduce efficiency.  Let me explain.  A wood fire is typically very inefficient.  A little heat is radiated out to heat someone, but most of the heat is convected up in the form of the fire.  A RMH captures a lot of that stray heat in the mass, re-radiating away later (still, some heat does escape through the chimney).  But in your electrical case, virtually all the heat is being radiated.  I suppose a water/oil/stone/etc. mass might buffer the effects of extreme heat radiation followed by periods of no heat when turned off. On the other hand, any heat conducted to a mass attached to a wall stands a chance to radiate outside, this lowering efficiency.

One other aspect to consider.  I don’t know where your electricity comes from (mine comes from coal—yuck!), but the thermal efficiency of a coal plant (or nuclear) is about 30-35% with some modern ones getting up towards 40%.  This is ignoring losses in transmission and converting voltage, etc.  If we use 40% efficiency from the coal/nuclear standpoint, then electrical heating is far less efficient than wood, natural gas, propane, or even coal burned right in your house for heat.  I don’t know if this last point matters to you, but it might be worth considering.  My personal thought is that in-home combustion is probably more efficient than electrical radiant heating in terms of heat generated from fuel consumed.

But back to your specific question, my personal thought is that electrical radiant heat is probably most efficient simply radiated out into the room.

Sorry if this is too long and convoluted a response, but I can hardly stop when talking about energy.

Eric
 
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That is an interesting question... First off you would want to make sure that that chimney is well and truly sealed so that your heat cannot escape through the stack. I would even say fit a piece of 2 inch foam to make sure dont just rely of flues or covers. After that... well it would be a very slow response way of heating so you would have to have it going way before you needed heat and then turn it off way before you did not need it. I could see some scenarios where it would be a good idea like if your utility does time of use billing and charges you less at night for example.
Hope some of that makes sense.
David
 
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My opinion is a bit different here. The chimney is going to be there, no matter what. All that brick is acting as thermal mass, whether it's heated or not. So if it's getting cold, you are increasing how much heat you need. If you are insulating it off anyway, I'd say adding any kind of heat to that thermal mass can only make things better. Face the heat  source to the brickwork, and see what it does.

I am in a rental with heat issues, I'm running an electric radiant heater when it's cold, and I have a short stack of landscaping blocks I hauled into the living room that the heater faces, with a slow speed fan in between them. Amazing what that does for this room! Without the blocks it's pretty well wasted, but the whole set up is VERY effective.

So my opinion is try pointing heat at your chimney, add a slow speed fan moving the heat from the thermal mass out of the area if you want, track what it does, it really might be very effective.

Is what you have the most efficient way to heat your thermal mass? That's a different issue, which other people have covered. But that thermal mass sitting there cold is not helping your overall heat levels, and I'd think anything you can do to heat it would be a net win. Use what what you currently have, it's worth trying, maybe you'll decide it works so well you'll come up with a better way to heat the mass.

:D
 
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Given that your fireplaces and chimney are in the center of the house, and the chimneys actually sealed, I agree with Pearl. At the least, the fireplaces are a good place to use for your electric heaters, already heatproof and safe. At best, using the mass of the masonry to moderate the heat output may make it a bit more comfortable in the rooms. I wouldn't see it increasing efficiency, but possibly improving comfort.
 
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