Why do infrared heaters work so well?

[RJM62]

If I remember my applied physics correctly, 1,500 watts should equal 5,118 btu / hr., no matter how you slice it. So why do infrared heaters seem to work so much better than other electric heaters?

Last year, on the first cold day, I set out to buy an electric heater. Living in a place with (relatively) cheap electricity, practically any electric heater is more economical than propane or oil, especially for the last 10 or 15 degrees. Most folks around here who use both tend to set the thermostat for the oil or propane heat to 55, and use the electric heat to bring it up to ~68 or so. It saves a lot of money.

The place where I lived last winter had a very good wood stove with a fan-forced heat exchanger. If I burned "Eco-Bricks" from Tractor Supply (a truly excellent product, by the way), I could easily keep the place at ~68 F even on the coldest of nights.

But after about four or five hours, I'd have to get up to refuel the wood stove, which was a drag. That's why I was looking for an electric heater -- to bridge those few hours so I wouldn't have to get up in the middle of the night.

When I got to the hardware store, 1,500-watt EdenPure heaters were moving like hotcakes at $275.00 each. (The regular price is $300.00.) I looked at the heater and thought it had to be some sort of rip off. I could get a 1,500-watt fan-forced ceramic heater for about $30.00. Could the EdenPure really be that much better?

I mean, 5,118 btu / hr. is 5,118 btu / hr. no matter how you slice it, right?

The manager saw me scratching my beard and came over, and we talked for a while. He basically said he didn't know why the EdenPure heaters worked so much better than other 1,500-watt heaters, but they did. He also said if I bought one, I could return it in two weeks for a full refund if I didn't absolutely love it.

So I bought one.

I still have it.

These heaters are very strange. If you put your hand in front of an EdenPure running at max throttle, it doesn't seem to be putting out a whole lot of heat. And yet they heat a room more quickly and efficiently than any other kind of heater I've used.

I remember last winter I went down to The City around the holidays, and I left the EdenPure turned on because I wouldn't be there to maintain a fire. I also had the oil heat set to about 50, just in case the EdenPure couldn't handle it alone. Again, oil was expensive and electricity cheap; so I was hoping the electric heater would be enough.

The outside temperature had gone down to 3 F. by the time I got back at about 2:00 a.m., but the inside temperature was ~62 F., using only the EdenPure to heat ~900 sq. ft. space (I had the unused rooms closed off for the winter). The oil furnace had not even come on. And mind you, that cabin wasn't the best-insulated place I'd lived in.

Getting a 60-degree F. temperature rise in a poorly-insulated cabin using only 5,118 btu / hr. seems like a mathematical impossibility to me. And yet there it was.

More recently (as in this morning), it was about 26 degrees outside when I woke up. Except for my bedroom (where I had the EdenPure), the inside temperature was 55, where the propane heat is set.

I moved the EdenPure from my bedroom to the living room / kitchen area, which have no wall between them. Together, I'd say we're talking roughly 600 sq. ft. of floor, with a total of roughly 60 or 70 square feet of glass in the doors and windows. Then I got in the shower.

When I got out of the shower ~10 minutes later, the temperature had risen from 55 F. to 68 F. Thirteen degrees rise in 10 minutes, on 5,118 btu / hr.

So, what it is about infrared heaters that makes them work so much better than seems possible given the math?

By the way, I have no horse in the race. I don't sell these things. But I was a skeptic about them until I bought one, taking a "math is math" attitude and harboring an unspoken condescension for the people who kept telling me that these heaters could do things that seemed mathematically impossible. But I'm a believer now. I don't know how they do it, but they do.

Any engineers / physicists / really smart people here who can explain this to me?

Thanks,

-Rich

 

[wabower]

When I worked for the natural gas company during the stone age, they said IR heated objects rather than air. It sounded good so I repeated it when selling them, but have no idea if it's accurate.

If I remember my applied physics correctly, 1,500 watts should equal 5,118 btu / hr., no matter how you slice it. So why do infrared heaters seem to work so much better than other electric heaters?

Last year, on the first cold day, I set out to buy an electric heater. Living in a place with (relatively) cheap electricity, practically any electric heater is more economical than propane or oil, especially for the last 10 or 15 degrees. Most folks around here who use both tend to set the thermostat for the oil or propane heat to 55, and use the electric heat to bring it up to ~68 or so. It saves a lot of money.

The place where I lived last winter had a very good wood stove with a fan-forced heat exchanger. If I burned "Eco-Bricks" from Tractor Supply (a truly excellent product, by the way), I could easily keep the place at ~68 F even on the coldest of nights.

But after about four or five hours, I'd have to get up to refuel the wood stove, which was a drag. That's why I was looking for an electric heater -- to bridge those few hours so I wouldn't have to get up in the middle of the night.

When I got to the hardware store, 1,500-watt EdenPure heaters were moving like hotcakes at $275.00 each. (The regular price is $300.00.) I looked at the heater and thought it had to be some sort of rip off. I could get a 1,500-watt fan-forced ceramic heater for about $30.00. Could the EdenPure really be that much better?

I mean, 5,118 btu / hr. is 5,118 btu / hr. no matter how you slice it, right?

The manager saw me scratching my beard and came over, and we talked for a while. He basically said he didn't know why the EdenPure heaters worked so much better than other 1,500-watt heaters, but they did. He also said if I bought one, I could return it in two weeks for a full refund if I didn't absolutely love it.

So I bought one.

I still have it.

These heaters are very strange. If you put your hand in front of an EdenPure running at max throttle, it doesn't seem to be putting out a whole lot of heat. And yet they heat a room more quickly and efficiently than any other kind of heater I've used.

I remember last winter I went down to The City around the holidays, and I left the EdenPure turned on because I wouldn't be there to maintain a fire. I also had the oil heat set to about 50, just in case the EdenPure couldn't handle it alone. Again, oil was expensive and electricity cheap; so I was hoping the electric heater would be enough.

The outside temperature had gone down to 3 F. by the time I got back at about 2:00 a.m., but the inside temperature was ~62 F., using only the EdenPure to heat ~900 sq. ft. space (I had the unused rooms closed off for the winter). The oil furnace had not even come on. And mind you, that cabin wasn't the best-insulated place I'd lived in.

Getting a 60-degree F. temperature rise in a poorly-insulated cabin using only 5,118 btu / hr. seems like a mathematical impossibility to me. And yet there it was.

More recently (as in this morning), it was about 26 degrees outside when I woke up except for my bedroom (where I had the EdenPure). The inside temperature was 55, where the propane heat is set.

I moved the EdenPure from my bedroom to the living room / kitchen area, which have no wall between them. Together, I'd say we're talking roughly 600 sq. ft. of floor, with a total of roughly 60 or 70 square feet of glass in the doors and windows. Then I got in the shower.

When I got out of the shower ~10 minutes later, the temperature had risen from 55 F. to 68 F. Thirteen degrees rise in 10 minutes, on 5,118 btu / hr.

So, what it is about infrared heaters that makes them work so much better than seems possible given the math?

By the way, I have no horse in the race. I don't sell these things. But I was a skeptic about them until I bought one, taking a "math is math" attitude and harboring an unspoken condescension for the people who kept telling me that these heaters could do things that seemed mathematically impossible. But I'm a believer now. I don't know how they do it, but they do.

Any engineers / physicists / really smart people here who can explain this to me?

Thanks,

-Rich

 

[Dale Young]

I have noticed THE SAME THING!!!
I used to live aboard a sailboat. One winter, I bought a couple ceramic heaters, and I already had a large square radiant-type ( red ribbon coil type) heater. The ceramic heaters would get STUPID HOT, but wouldnt warm the boat. BUT the square infra-red one of same wattage WOULD! Not only would it warm the boat, it warmed a little too well at times. I have always wondered why! I had always guessed that it was warming not only the air in front of it, but also whatever surface it was facing. I dunno!!

 

[Dale Young]

Wayne, You JUST beat me to it!! But thats what I figured!

 

[DaleB]

A friend of mine has a gas-fired ceramic IR heater in his garage. The air temperature can be 30-40 degrees out there, but you pick up a tool or a part that has been laying around, it's warm. So, yeah -- the IR heats the stuff in the garage, but not just by heating and circulating the air.

 

[Tom-D]

Because they work on the same principal as the sun.

 

[DaleB]

Because they work on the same principal as the sun.

Duh.

Excellent point.

 

[Jim Logajan]

When I worked for the natural gas company during the stone age, they said IR heated objects rather than air. It sounded good so I repeated it when selling them, but have no idea if it's accurate.

Concise and accurate to the extent I understand heat transfer.

For the technically inclined with hours to spare, there is a heat transfer e-textbook that goes into the nitty gritty of this stuff and it seems reasonably good and costs nothing - a result of MIT's "OpenCourseWare" initiative: http://web.mit.edu/lienhard/www/ahtt.html

 

[RJM62]

Ah, okay. That explains it.

Thank you,

-Rich

 

[Sac Arrow]

A friend of mine has a gas-fired ceramic IR heater in his garage. The air temperature can be 30-40 degrees out there, but you pick up a tool or a part that has been laying around, it's warm. So, yeah -- the IR heats the stuff in the garage, but not just by heating and circulating the air.

Because they work on the same principal as the sun.

Yes.

(Says one that has taken like a bazillion heat transfer courses)

 

[RJM62]

Yes.

(Says one that has taken like a bazillion heat transfer courses)

Okay, then here's a sub-question, of sorts.

When I opened the EdenPure up to find out what made it tick, it seemed to me that what they basically do is just enclose ceramic heating elements inside of copper (?) cylinders, and blow the air past the cylinders rather than over the elements themselves.

How does adding the extra step of transferring heat from ceramic elements to copper cylinders and blowing air over them, rather than just blowing the air directly over the elements, make the heater more efficient?

I'm not saying that it doesn't work, by the way. It's pretty obvious to me that the concept works. It's the how and why that baffle me. I would think adding the extra step would result in reduced, rather than increased efficiency.

-Rich

 

[Sac Arrow]

Okay, then here's a sub-question, of sorts.

When I opened the EdenPure up to find out what made it tick, it seemed to me that what they basically do is just enclose ceramic heating elements inside of copper (?) cylinders, and blow the air past the cylinders rather than over the elements themselves.

How does adding the extra step of transferring heat from ceramic elements to copper cylinders and blowing air over them, rather than just blowing the air directly over the elements, make the heater more efficient?

I'm not saying that it doesn't work, by the way. It's pretty obvious to me that the concept works. It's the how and why that baffle me. I would think adding the extra step would result in reduced, rather than increased efficiency.

-Rich

I'm not familiar with Edenpure but after a quick Google it appears to be a convective space heater using IR elements. But to answer your question the elements themselves don't generate enough conductive heat to make convective space heating efficient, so they use ceramic elements to absorb IR heat.

Whether or not that's more efficient than a resistance heater I don't know. I guess it is.

 

[jesse]

If I had to guess I'd say it's because it cost a fortune and your mind helps you justify it, like my Macbook Retina

 

[RV10flyer]

A heat pump or high eff gas furnace with supply air blowing on the outside walls will do a great job heating too and more efficient than those electric heaters if trying to heat an entire house. If I just wanted to heat one room and set the main system back to 60F sure you will save money but not heating the entire house. Of course you said you had a well insulated home and that makes a world of difference especially with windows and doors. I have been in houses with 4 of those heaters and have not seen any evidence of a lower than average power bill. I would have put the $1500 into a 15 SEER HP system myself.

 

[RJM62]

If I had to guess I'd say it's because it cost a fortune and your mind helps you justify it, like my Macbook Retina

LOL, maybe, although then I'm one of many, many people who are similarly deluded. People sometimes line up at the truck (seriously) to buy infrared heaters around here.

-Rich

 

[RJM62]

A heat pump or high eff gas furnace with supply air blowing on the outside walls will do a great job heating too and more efficient than those electric heaters if trying to heat an entire house. If I just wanted to heat one room and set the main system back to 60F sure you will save money but not heating the entire house. Of course you said you had a well insulated home and that makes a world of difference especially with windows and doors. I have been in houses with 4 of those heaters and have not seen any evidence of a lower than average power bill. I would have put the $1500 into a 15 SEER HP system myself.

That's basically what I do. I have the registers upstairs closed (the heat that rises up the stairs is enough to prevent pipes from freezing), and the heat on the furnace turned down to 55. I used the electric heaters to heat the room(s) actually being used at any given moment.

About the only time I turn the furnace up to 68 is if I have overnight guests. This is both because I need the heat upstairs (so I open the registers); and because if I schlepped the EdenPure up and down the stairs as needed, they'd know what a tightwad I am.

-Rich

 

[Lawreston]

Consumer experience: Several years ago I was interested in the EdenPure. If Paul Harvey endorsed it, must be good, eh? ) Researching the product I read many comments that indicated element replacement could be "too often" and expensive. There were other negative comments, so i didn't purchase.
My house is three story, the bottom, finished level is 500+ sq. feet and sits, at the east side 12 or 13 feet below ledge that was blasted before foundation was poured. It's the family room and studio with much furniture and hot tub, so I spend a lot of time right here.
I bought the Comfort Zone unit which is competition to the EdenPure. Though the main heating system is oil-fired baseboard, the Comfort Zone will quite quickly add 4° to 5° to the temperature in the room. This will be the 5th winter; I've never had to replace the heating element. The 3rd floor(master BR, guest room, full bathroom) I run a bit cooler on the 3-zone system. Cooler temps. having come recently, I've put the Comfort Zone into the 3rd floor bathroom; and in short order it's warm enough that there's no condensation from the hot shower and sure beats cranking up the 3rd floor thermostat for a shot duration. Comfort Zone has a new version upgrade available; I might just buy a 2nd unit. But beware: there are other units on the market that look like the EdenPure unit and are less expensive. Inferior! (I'm not employed by Comfort Zone.)

HR