{HEAD ~ The assembly} comprises {TAIL ~ a housing} 14 generally containing a propane or natural gas fired furnace 16 with supply duct 18 
comprises
{ HEAD ~ The assembly } comprises { TAIL ~ a housing } 14 generally containing a propane or natural gas fired furnace 16 with supply duct 18
HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH