The answers are complicated and located here: http://www.heatpro.us/designtree/documents/C50A025C4A1CACEC77F1C2B34CE7FBEE228C9569.html http://www.heatpro.us/purgeairtree/ www.heatpro.us energy businessmen's knowledge Yes, you really have to find out the MAKE and MODEL to get good answers. There IS more than one machine made.
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