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??

If the old unit is defective and even if fixed would put out CO then it would be best to replace it. I am a firm believer in getting a second opinion from a different local company so I suggest you do that also.