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Guru

Join Date: Jul 2008
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Most Cost-Effective Portable Electric Heater

10/15/2008 12:23 AM

While the prices for energy are coming down, heating oil among them, the pending arrival of winter is bound to send prices climbing again.

I need to come up with a safe supplemental source of heat. A friend of mine raves about the new electric heaters he's purchased. They work so well , he went out and bought three more. His electric bills do not appear to have been heavily impacted. I suspect they are ceramic units.

I need a method for keeping my shop warm while room-cure epoxy hardens and would like not to have to use propane like I did last year. I've made a frame for holding 8 infra red bulbs above the mold but I'm uncomfortable leaving it unattended. As effective as he says it is, the unit my friend bought is a bit costly.

Might some of you suggests what you believe is the most cost effective electric heater? The one with the highest BTU's per watt? Or am I kidding myself?

Thanks

L. J.

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Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

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#1

Re: Most cost effective portable electric heater

10/15/2008 8:01 AM

Electric heaters are almost 100% efficient. Almost all the electrical energy supplied to them appears as heat.

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United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain - possibly to become "South Scotland" or "Non-Caledonia" from September 2016. Kettle's on.
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#2

Re: Most Cost-Effective Portable Electric Heater

10/15/2008 9:16 AM

http://www.simetric.co.uk/sibtu.htm states that 1BTU/hr = 0.2928751W.

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Guru

Join Date: May 2006
Location: Placerville, CA (38° 45N, 120° 47'W)
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#3

Re: Most Cost-Effective Portable Electric Heater

10/15/2008 11:07 PM

I didn't search, but there was an extensive thread on this about a year ago. As PWS said, all electric heaters convert essentially 100% of the electric energy they receive into heat energy. Any differences in overall efficiency will be due to getting as much as possible of the heat energy to the desired location and as little as possible to places where it isn't needed or desired.

For spot heating, this would imply the need for a good reflector that can easily be kept clean, and focuses the heat into the required area.

For human comfort, there are a slew of other variables...

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#4

Re: Most Cost-Effective Portable Electric Heater

10/15/2008 11:33 PM

Cost per BTU is highest for electric resistance heating. The only way it makes economic sense is if you want a hot spot and are only heating a small volume of air.

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Guru

Join Date: Apr 2008
Location: Chicago
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#5

Re: Most Cost-Effective Portable Electric Heater

10/15/2008 11:45 PM

Last week I was building up a latex mold in my studio, other times I use a two part silicone mold material, and they both cure more readily in elevated room temperatures.

To do so safely, I like to use a ceramic heater that will blow in and through a well ventilated cardboard shroud that covers the mold within a few inches of the surface.

The nice thing about this setup is that I'm not paying to heat more space than the mold occupies, and the cardboard will never reach combustion temp.

I also make sure that the portion of the mold closest to the heater is nearly a foot away. plenty distance in my case, but I'm unsure of your application.. details?

I do the same with the urethane epoxy.

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Commentator
Hobbies - Fishing - New Member but not a new fisherman Hobbies - Target Shooting - New Member

Join Date: Apr 2008
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#6

Re: Most Cost-Effective Portable Electric Heater

10/16/2008 12:15 AM

It should go without saying that electric heaters could be an ignition source especially in an industrial environment where vapors and/or fumes may exist.

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Guru

Join Date: Jul 2008
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#7

Re: Most Cost-Effective Portable Electric Heater

10/16/2008 12:16 AM

I appreciate the responses. Thanks

It appears that the best solution for my application will be to purchase several gutter heaters like those sold in home centers to prevent structural damage from ice in the winter.

Mine is an all steel bench made of heavy gauge metal (0.125") I'll figure out a method of securing the gutter heaters in an effective pattern on the underside of the bench. Then cut off the thermostatically controlled switches and hook up the heaters to a Variac auto transformer. The vacuum pumps (220 volt) are on a seperate pair of CB's so I should be able to power the heaters without overloading their 110 volt circuit.

With the gutter heaters below and the infra red lamps above, the epoxy should harden up really well and fast. It should also go beyond the Glass transition temperature needed.

If you smell something burning. . . . . !

Thanks again

L. J.

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Guru
United States - Member - Charter Member Engineering Fields - Instrumentation Engineering - Charter Member

Join Date: Mar 2008
Location: The People's Republic of Massachusetts
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#11
In reply to #7

Re: Most Cost-Effective Portable Electric Heater

10/16/2008 7:44 AM

You could also try under soil heaters. The wire type comes in a few lengths and wattages. I use these in my plant propagators and they work great.

http://www.littlegreenhouse.com/accessory/heaters3.shtml

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Power-User

Join Date: Apr 2007
Posts: 126
Good Answers: 15
#8

Re: Most Cost-Effective Portable Electric Heater

10/16/2008 12:32 AM

Hi L. J.,

How Do You Do ., A " safe supplemental source of heat " , You Say ? If portable is not required :

If I May Ask, Do You Get That Thing We Residing, In The Confederate States Of America Call - Sun ?

Just kidding, Of course, you do and If you have a well lit wall area, during some of the working day you could easily, construct a box to capture that Sun light and pipe the heat back into your shop very safely and without hardly, any expense at all. We build these all the time , from any material available and simple Black Painted ,2 x 4 sided , plywood bottom boxes , covered by double 6 mill poly will last the winter and beyond as a fine Solar collector .

The box should be divided vertically & horizontally a bit too , to allow the air to rise and heat up a bit, before its return to your shop and a small bathroom fan pushing 100 CU FT a minute will do the trick, as your prime mover fan hooked by a short pipe out to the box.

Therefore , One Should Mount This Solar Air Heater on the Sunny wall, so as to draw air from down at your foot level and return at your head height or higher and move all building air about the building , with ceiling fans .

A 4 x 8 collector should heat up a 9 foot high area , of 1000 SQ FT, pretty nicely all day. If not, add another one , as they don't cost much to build this way.

No electricity purchase would be required if a 12 volt fan moved, by a very small PV panel, could be employed and in AC Or DC , common HVAC thermostats , can be set to come on or go off , at temperatures easily attained during , the very first Sun Shine, of the morning .

While this specific design is not, the one were working on today in mass production, we are about to introduce devices for sale, from my company that work in the same general fashion , and so I can say , this is a very long and true tested method of inexpensive heating, of a structure.

For most modern buildings, it can replace the heater, in use during the Sunny hours and a good bit beyond too , if that structure is built and insulated properly.

I invite you and everyone here at CR4, to join me , at a new group we just formed , to discuss this and other shelter related topics at: http://finance.groups.yahoo.com/group/georgiaadobeforums/?yguid=336472111

I do hope this helps you and your friend, this winter , to stay warmer.

Best Regards,

Joe Woodall, Managing Partner

Georgia Adobe LP Rammed Earth & Renewable Energy

2395 Bowman Hwy. NW.

Dewy Rose GA 30634 CSA

706-213-7693

http://www.georgiaadobe.com

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Guru

Join Date: Jul 2008
Posts: 929
Good Answers: 55
#9
In reply to #8

Re: Most Cost-Effective Portable Electric Heater

10/16/2008 1:04 AM

Hi "Georgia"!

I very much appreciate the well thought out reply and the suggestion.

However, as nice as it is, there are two obstacles that preclude implementing your solution.

1. The composite bench is in an unheated basement with tiny windows. The only heat is whatever there is lost from a the boiler that heats the upstairs house At night, it shuts down as I prefer a cold room and an electric blanket although my cats would likely disagree. So there is no heat in the basement at night during cures unless I provide it by some alternate method. Hence this public request for suggestions.

2. That side of the house never sees the sun. It faces Northeast and there is a tall mountain close by that blocks direct rays.

An interest in solar heating and solar electric panels died rapidly when a tech type surveyed the property.

Thanks

Art

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Power-User

Join Date: Apr 2007
Posts: 126
Good Answers: 15
#10
In reply to #9

Re: Most Cost-Effective Portable Electric Heater

10/16/2008 1:16 AM

Hi Art,

Then perhaps a self built solar to water collector piped to the basement , held in a self built tank, to be pumped and used/heated from anytime desided would work ?

An Automobile radiator & box fan will work as a heat exchanger. Just a side thought but heat storage is KEY .

Joe

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Power-User

Join Date: May 2007
Location: Los Angeles area, California, USA
Posts: 202
Good Answers: 9
#13
In reply to #9

Re: Most Cost-Effective Portable Electric Heater

10/16/2008 10:42 AM

As in all real estate analysis considerations, the three most important points are;

1. Location

2. Location

3. Location

MR. GUY

Hi "Georgia"!

I very much appreciate the well thought out reply and the suggestion.

However, as nice as it is, there are two obstacles that preclude implementing your solution.

1. The composite bench is in an unheated basement with tiny windows. The only heat is whatever there is lost from a the boiler that heats the upstairs house At night, it shuts down as I prefer a cold room and an electric blanket although my cats would likely disagree. So there is no heat in the basement at night during cures unless I provide it by some alternate method. Hence this public request for suggestions.

2. That side of the house never sees the sun. It faces Northeast and there is a tall mountain close by that blocks direct rays.

MOVE HOUSE

An interest in solar heating and solar electric panels died rapidly when a tech type surveyed the property.

Thanks

Art

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Commentator

Join Date: Sep 2006
Posts: 69
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#12

Re: Most Cost-Effective Portable Electric Heater

10/16/2008 9:39 AM

Seems to me you're wasting a lot of energy heating that steel work table. Perhaps you could isolate the work surface. For instance, you could construct a removable surface with the built in gutter heaters you suggested that only heats a volume above the steel table and box it in as a previous CR4er suggested. An insulating layer would keep heat from passing to the table surface, and if cleverly constructed, could be removed as a unit when thwe weather gets warmer.

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Guru

Join Date: May 2007
Location: Geelong, Australia
Posts: 1089
Good Answers: 54
#14

Re: Most Cost-Effective Portable Electric Heater

10/16/2008 6:29 PM

Electricity is usually an expensive way to heat a room, but if you have to use it consider using a reverse cycle air-conditioner. The good ones give up to 3X has much heat out as is used to run them.

That's 1000W in, to give 3000W out. the Out/In ratio is listed as C.O.P. (coefficient of performance). Unfortunately many lower quality units aren't any better than unity.

Personally, I just put on another woolly jumper.

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#17
In reply to #14

Re: Most Cost-Effective Portable Electric Heater

10/18/2008 5:32 AM

ffej said:

"That's 1000W in, to give 3000W out. the Out/In ratio is listed as C.O.P. (coefficient of performance). Unfortunately many lower quality units aren't any better than unity"

You mean a "heat pump" ?

How can this be? You are running a compressor and that has to cost you.

Are you sure about this? If so please enlighten me.

I have never heard of any electrical device that outputs more than the input power. You also have a compressor and other components that wear and will need eventual servicing and/or replacement and the initial capital expense is quite high. You can buy a resistive type heater for 50 bucks or less.

Ed

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Associate

Join Date: Mar 2008
Posts: 25
Good Answers: 2
#15

Re: Most Cost-Effective Portable Electric Heater

10/16/2008 6:50 PM

I have 3 questions for you. How big is the area needed to heat the molds? How hot does it need to get, and does it need to have any ventilation? This may help us give you a better answer.

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Guru
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#16

Re: Most Cost-Effective Portable Electric Heater

10/18/2008 3:33 AM

Hello Laughing Jaguar;

I use a 15" parabolic dish heater aimed at a 4' x 8' piece of roofing tin

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Anonymous Poster
#18
In reply to #16

Re: Most Cost-Effective Portable Electric Heater

03/16/2009 4:51 PM

Have you looked into portable infrared heaters? The CZInfrared( http://www.czinfrared.com/ ) is a great, efficient portable heat source. While it's true that almost all portable heaters are 100% efficient in producing heat from electricity, most types of heat can be quickly lost to drafts, poor insulation, etc. This means a loss of efficiency in the end. Infrared heat directly heats objects in the room, and they in turn warm the surrounding air. Also, you are saving money by zone heating the areas you need instead of heating your entire house.

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Users who posted comments:

Anonymous Poster (3); Bricktop (1); bwire (1); dkwarner (1); ed fuzzyE kedz (1); ffej (1); Georgia Adobe (2); guitarhunter (1); JE in Chicago (1); Laughing Jaguar (2); Mr. Guy (1); PWSlack (2); whyme (1)

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