Old gas fired Sears floor furnace model #138-737630. Local HVAC said (only pulled top grid off - did not go under house and look at it) it needed a gas valve which would probably be around $500.00 for the parts and labor. Also said I should replace unit ($2709.00 for new unit) or around $10,000 for a new central heat unit to cover downstairs of house only (6 rooms) and in addition I would have to hire a carpenter to repair floors and do the duct work and venting, etc. Said if I just repaired the existing unit I'd still be getting carbon monoxide all the time. What are your opinions please??