Furnace air filter question
At the risk of giving you the wrong advice, I would say that the 'wrong size' shouldn't be used. HOWEVER, some units can operate safely AND effectively this way.
The BEST advice I have is to either contact the Mfgr. or to take the Mfgr. info to an HVAC Supply House for more guidance.
My best to ya and hope this helps.
Jay J -Moderator
PS: God Bless America!