My parent's put a solar air heater on our house about 30 years ago and i need to locate replacement parts. it was installed by, Solar Electric Inc. West Branch Iowa 52358. model # DN21. I called the phone number on the tag and it is now a residential #. the lady that answered said they had the number for 16 years and that she get calls weekly for them. ANY HELP WOULD BE GREATLY APPRECIATED, THANK YOU.

Probably went out of business. Generally the parts are not made by the manufacturer of the solar system. They are typically off-the-shelf components made by other companies so try to find the manufacturer of the defective part or a comparable replacement.