Greetings,

I have an old electric furnace in my attic that keeps burning up heating elements.

This is a very old unit and unfortunately I cannot locate the mfg/model information on the unit. I'm estimating it to be 20+ years old.

I have purchased replacement "restring" kits (Napco D500) which are easy to install, but are to long to work properly. In order for these elements to work properly they need to be stretched to allow airflow through the coils, otherwise they burn apart. If I stretch them long enough to allow proper airflow they become way to long to fit the element rack. The D500 part states it is a 5KW replacement and correct length is 41" - 135".

I replaced all three elements yesterday and they burnt apart in 1 1/2 hours! :mad:
Also, I removed and scrubbed the fan unit and the coils look pretty clean before installing the replacement elements.

The "original" elements were made of very thin ribbon metal ~1/8" wide and very thin with a length of ~32". They look something like a curly-q french fried potato. I cannot find this part anywhere nor does any supply shop recognize the part.

Does anyone have any suggestions how to fix this problem?
1. Any suggestions where I might find the "original" elements, or
2. How I might shorten the D500 part so that it is stretched correctly and also the proper length for the rack?

Note: The D500 has machined on connectors at each end.
Here's a so-so picture of the D500:
http://www.myhvacparts.com/Catalogue/Electric%20Furnaces%20and%20Air%20Handlers/Electr2.jpg

Follow-up:
I found Mfg/model information.

Mfg. No. NAXD004AH02
Model No. NAXD004AH02 867.823322
Style No. 15IBH-240083
Serial No. H703 55976
208/240 VAC
1 Phase
60 Hz
15 KW @ 240 VAC

Sounds like that unit is a ICP (InterCity Products design). There old units had what we used to call old toaster elements because they were made like a ribbon as you say.

If this is for real the price is way to high.

http://www.expertappliance.com/partfinder.php


You might try a lower watt kit. They are shorter but you will have a decrease in output.

You might try a lower watt kit. They are shorter but you will have a decrease in output.

I spoke with a local HVAC service technician yesterday evening who suggested the same thing. It seems to all boil down to the fact that there is not enough gap between coils and as a result they burn apart. He suggested trying a shorter 3KW or 3.5KW kit and see if the results are better, albeit with a reduced output. He also talked me through switching the blower motor to high speed from it's normal low speed to generate more airflow.

AFWIW, after a closer look at the "original" elements they appear to be copper.

One follow-up question. On the whole the unit seems to be in good working condition, considering that I've dismantled and cleaned most of it now. Is it possible to replace the entire "heat unit". Not the whole furnace cabinet, coils, fan, etc, just the part where the heating elements live. Is it possible to replace that piece with a more modern and easily serviceable unit that has the same output (15KW) specification?

Many thanks for your help and advice.

I was thinking that myself yesterday but didn't want to send you astray. That is, the combined size of those new elements, their unconventional stretched configuration, proximity to each other, number of elements, and lack of airflow is overheating the elements.

It might be possible to replace the air handler with a newer unit and swap in your older coil. That gets into some labor and cost to draw down your system and swap air handlers. Its impossible to tell from here, but it couldn't hurt to get some quotes and opinions that you should only trust with eyes-on.

The original elements were copper alloy.

Hi DAC122,
Thanks for your input.


I was thinking that myself yesterday but didn't want to send you astray. That is, the combined size of those new elements, their unconventional stretched configuration, proximity to each other, number of elements, and lack of airflow is overheating the elements.
All indications, advice, parts shop/professional comments, and Internet searches point in this same direction. I have to question if the unit really produced 15KW when new. As stated in my original post, not only did the three new 5KW elements burn out, but they also completely fried the three new limit switches I replaced. Not just tripped them, but ruined them.


It might be possible to replace the air handler with a newer unit and swap in your older coil. That gets into some labor and cost to draw down your system and swap air handlers. Its impossible to tell from here, but it couldn't hurt to get some quotes and opinions that you should only trust with eyes-on.
I was thinking more along the lines of just replacing the heating element piece and not messing with the coils, fan, or cabinet. The heating elements look to be a separate modular unit bolted into the cabinet on the opposite end from the coils. To me it looks like the unit could be unscrewed and replaced with a modern unit of the same size/output. But I'm a complete novice and not sure if that is really possible and/or what the ramifications might be.

I was thinking more along the lines of just replacing the heating element piece and not messing with the coils, fan, or cabinet. The heating elements look to be a separate modular unit bolted into the cabinet on the opposite end from the coils. To me it looks like the unit could be unscrewed and replaced with a modern unit of the same size/output. But I'm a complete novice and not sure if that is really possible and/or what the ramifications might be.

Without seeing it, it would be impossible to offer an opinion, but I think you are thinking on the right lines. I think you'd be more successful with this approach than customizing a heat strip to a shorter length.

Thanks to you both for the advice.

I guess the next move is to get an estimate on changing the heat unit.

Best regards,
Greg

For what it is worth, a higher blower speed may generate more air flow but not necessarily more heat. In fact it could have the exact opposite effect.