4' Baseboard Heater

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Re: 4' Baseboard Heater

Hello Don

I understand you can't use the 120 volt to figure this because your 8.33 amps. will be 16.66 and that would make the output come 4000 watts.

I was going through my HVAC books and found this formula. It is in Audels volume #3 text book on Heating Ventilation and air conditioning Library.

That is one reason I did not put the fugures in it, it come out to around 3000 watts.

I agree with everyone on here without knowing what the extra 120 volts will do to the resistance of the resistor or heating element we need to use 14.45 ohms. And if it where designed to be a 240 volt unit it would be 28.91 ohms which would make it 2000 watts.

It is a legitimate formula who am I to say it is wrong?

Ronald :)
 
Re: 4' Baseboard Heater

Ron,
It is a legitimate formula who am I to say it is wrong?
Click to expand...
Just because it is published in a book or on the net does not mean that it is correct or legitimate.
Don
 
Re: 4' Baseboard Heater

Don I respect your opinions more than most on this site.

But until you can prove that formula is wrong I am willing to accept it.

If you want to remove it because you think it is misleading I promise there will be no hard feelings.

But I have shown documentation on two or three other things from the NEC handbook and have gotten the same feedback from others just because they want admit they are wrong.


Ronald :)
 
Re: 4' Baseboard Heater

Ronald, one of my jobs is to check books for technical accuracy. The author, just like everyone else, has an opinion. I have found numerous errors in every book I have ever checked. What I am saying is that no one is perfect. Don has made a very valid statement when he said, "Just because it is published in a book or on the net does not mean that it is correct or legitimate." :D
 
Re: 4' Baseboard Heater

Thanks Charlie we are just human and we all make mistakes.

I don't know if the formula is correct or not,like I said I just posted it for conversation but didn't mean for it to be all negative or to cause any hard feelings.


Charlie and Don I don't believe everything I read from the net and papers but I would like to think I can put some faith in a trade text book.

Do you or Don either one know for a fact that this formula is not valid?

I don't think anyone should degrade the literature in this text book just for sake of making a argument on this site.

But now I would like to know if the formula is valid or not?

Like Rattus said the resistance would change as the temperature gets higher I would assume it would be higher than 14.4 ohms and if so the output might not be 4000 watts.


Ronald :)
 
Re: 4' Baseboard Heater

The formula in the referenced book must be wrong, or it is a simplified formula being used out of context.

Take the formula for the power of a heater P=I^2R, so with R constant we get:
Pnew = Inew^2 x R
Pold = Iold^2 x R
resulting in Pnew = Pold x (Inew^2)/(Iold^2)

Now use the formula for voltage E=IR and do the substitutions we get:
Enew = Inew x R
Eold = Iold x R
resulting in Inew = (Enew/Eold)/Iold

Substituting this into the power formula we now have (not all steps are shown):
Pnew = Pold x (((Enew/Eold)^2)/Iold^2)/Iold^2
Which reduces to:
Pnew = Pold x (Enew/Eold)^2

So in this example: Pnew = 1000 x (240/120)^2 = 4000W
 
Re: 4' Baseboard Heater

Thanks for the reply Jim I would think this is a simplified version.

But how many here think we can use ohms law straight out here? I would think there would at least be a constant to multiply the ohms or amperage at 120 volts value with to compensate for the change in resistance.Than just multiply it by 16.6 amps and get 4000 watts? We all agree that the resistance isn't geared for 240 volts do you think the Resistance would be constant at these extreme temperatures?

Ronald :)
 
Re: 4' Baseboard Heater

Jim you know I'm as dumb as a rock in math and make no bones about it.

But in this formula 120 volts is subtracted from 240 volt between the brackets not divided.


So in this example: Pnew = 1000 x (240/120)^2 = 4000W
Here is a photo of the page

:)

[ January 31, 2005, 09:52 PM: Message edited by: ronaldrc ]
 
Re: 4' Baseboard Heater

The text implies that this is a simplified formula for use with a voltage difference of approx -9% and not for use with an increase in voltage at all.

Additional comment
This is a case of Ohm's Law. The resistance of the heater element is determined by it materials and method of construction. The fact that the value of resistance may change with temperature (and we don't know that it will) is not important as we are dealing with approximations anyway.

[ January 31, 2005, 11:15 PM: Message edited by: jim dungar ]
 
Re: 4' Baseboard Heater

Jim I agree with you but I also read that you will probably burn your heater out if you go about +10 at 120 or +20 volts at 208,230,240 or 277. :)
 
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