| 摘要 |
Ducting for use in a heating system, said ducting having first and second passageways, one of which communicates with air supply means for said heating system and the other of which communicates with exhaust means of said heating system, each of said passageways being open at at least one end so that the said one of said passageways can supply air to said supply means and exhaust gas can expel from the said other of said passageways. |
