Baseboard efficiency question

[thalpin]

Hello all, I was told in my level I course that by painting the metal fins of your typical electric basboard heaters that you can increase their efficiency by 15-20%. I am assuming this is increasing the heating fins emmissivity. Can anyone explain this a little better so I am clear on this. I am also assuming that the color of the paint is not so much a factor as color does not effect emmissivity greatly. Any thoughts are appreciated. Thanks, Tim

[Brian A. MacNeish]

Originally Posted by thalpin

Hello all, I was told in my level I course that by painting the metal fins of your typical electric basboard heaters that you can increase their efficiency by 15-20%. I am assuming this is increasing the heating fins emmissivity. Can anyone explain this a little better so I am clear on this. I am also assuming that the color of the paint is not so much a factor as color does not effect emmissivity greatly. Any thoughts are appreciated. Thanks, Tim

Haven't heard that before and can't see it giving much of an increase, if any, in efficiency. Finned heating element baseboards (hot water baseboards also) are not radiant heaters but convective heaters. IMHO, if you want to maintain/increase effciency over time, vacuum accumulated dust from the fins and staighten any that are bent to allow good airflow through the fins to deliver heat to the room.

Now that we're back into another energy crunch like the 70-80's, I'm hearing a lot of "on the street" info that may have an element of truth (scientific fact) in it but is generally terribly off the mark. I may dig into my archives and find my "smoke and mirrors" list of 85 or so "popular energy misconceptions" that I drew up in my spare time as I wrote and managed our province's energy regulations and was a public energy advisor.

"On the street" energy advice from your doctor, lawyer, barber, etc compares with getting stock tips from a cab driver!! Energy efficiency and energy conservation is now a specialty field which is not learned from a book or a periodical article only; you must work in all elements from the academics through to building analysis/HVAC design and installation (audits, thermal boundary/envelope design, heating loads, installing) to really get the full understanding and appreciation of what's really achievable when "it's done well"!!

Last January, Joe Lstiburek was in Halifax to speak at the bienniel (used to be yearly) ENERhouse conference sponsored by my old gov dept and the private homebuilders association (he's been brought every 2-4 years since 1984!!). He was being interviewed by CBC (our national radio system) and was asked about LEED. His quick and to the point answer, "It doesn't work!!". Later he said "We should only give these awards after a few years of operation when the design/systems have proven themselves and met or exceeded the design criteria." Makes a lot of sense. Looks good on paper but so did the TITANIC.

For example: A couple of years after I took the gov job here, I was called to the field by the top local energy retrofitter after he had been called to consult on an award winning modest 5 year old house suffering severe wood siding/sheathing rot. The architect still has the award on his wall, yet there was $20,000 (1994 $) costs of replacing the exterior elements. IMO, this award should be taken from him.

[Joe Funderburk, CMI]

My brain is telling me it would decrease efficiency. But If there is any increase at all, I don't know how one can make a giant toaster efficient enough to be a practical method of heating today.

[Jeffrey Moore]

Test a small section. Paint a fin with high emissivity paint and then
look at the temperature difference with your thermal camera.

[Keith Runquist, CMI]

That sounds really screwy. Those baseboard heaters get hot enough to burn the paint. If it was a good idea they would come painted. About 1/3 of the homes around here use electric baseboard for the primary heat source. My own house included. Very efficient heat. We heat for less than $1 a day except in the coldest months and then it might go to $1.50 a day. I've never seen them painted and I can't imagine why you would do that.

[Joe Funderburk, CMI]

Originally Posted by krunquist

Very efficient heat. We heat for less than $1 a day except in the coldest months and then it might go to $1.50 a day.

Are you saying your electric bills are $30 to $45 per month?

[Joe Funderburk, CMI]

"Because of electricity generation and transmission losses, electric heat is often more expensive than heat produced in the home or business using combustion appliances, such as natural gas, propane, and oil furnaces....If electricity is the only choice, heat pumps are preferable in most climates, as they easily cut electricity use by 50% when compared with electric resistance heating."

http://www.energysavers.gov/your_hom.../mytopic=12520

[Jeffrey Moore]

Keith,
I hope the OP is smart enough to use high temperature paint.
Some are rated up to 1200 degrees. Spray cans of the stuff
used for wood stoves and such run around $10.00.

So, I don't think the suggestion is so screwy.

Depending on the material used in the heater, the emissivity
of paint can be higher.

[Bob Elliott]

Originally Posted by jfunderburk

"Because of electricity generation and transmission losses, electric heat is often more expensive than heat produced in the home or business using combustion appliances, such as natural gas, propane, and oil furnaces....If electricity is the only choice, heat pumps are preferable in most climates, as they easily cut electricity use by 50% when compared with electric resistance heating."

http://www.energysavers.gov/your_hom.../mytopic=12520

So why are so many people claiming they save money by running those little space heaters made by Pilgrims or Amish haha.

I think electric can be cheaper if used strategically , such as only in rooms being used.

Hard to do that with normal HVAC.

[Jason Kaylor]

I could be thinking wrong here, but I would think that using a super reflective surface would actully be more efficient.

It would be an easy test. Use low E paint on the fins and put something refelctive in the back of the unit. Then do a second unit using high E materials. Put a thermocoupler (or an ambient temp meter) a few feet in front of the units, and take the readings. IR readings on the unit will only show its temp. We need the temp of the space being heated, not the unit. It seems to me a hotter unit would actually be less efficient and possibly dangerous.

JJ

[Bob Elliott]

Reflective surface does help.
It is the same thing as the old trick of taping aluminum foil on a wall behind your radiator.

The foil actually reflects the heat.

[rbibler]

I think he miss under stood something in his class. If you paint a metal surface you camera can then pick up the correct temps...

Best

Ron

[Brian A. MacNeish]

Originally Posted by belliott

Reflective surface does help.
It is the same thing as the old trick of taping aluminum foil on a wall behind your radiator.

The foil actually reflects the heat.

The foil actually reflects the radiant portion of the heat (which can be substantial from an old cast iron rad), but there is also a fairly large heat transfer by convection and very little by conduction (except at the radiator/air boundary layer)

[measter]

All concerned,

A reflective paint won't help. You aren't reflecting heat like you are with a piece of aluminum behind a wood stove. flat black paint won't help either. It may transmit heat FASTER, but it won't transmit more heat per W-hr. So therefore it's won't be more efficient.

As Ron pointed out, the experiment with the thermal camera won't work. The temperature of the fins will be the same regardless of the color. The temperature reading of the flat black paint will only be more accurate when the emissivity of the camera is set close to 1.0.

The interesting thing about electric heat is that it is close to 100% efficient at the source. I'm not counting the 67% average loss of energy during transmission to the appliance.

So to make a short story long - there isn't really any efficiency to be gained with a device that is almost 100% efficient. Unless you move closer to the power plant.

[David A. Andersen]

Oh my, my, my.......

Oh so many misconceived theories.

I'll let you all hash this one out for a while and see if someone hits on it.

Tim, don't second guess what you learned.
Go back and read it again. That should clear things up!
Consider a steam or hot water radiator instead of an electric baseboard heater though (less confusing). Once you get that, you can add the complexities of electrical efficiency.