furnace certification

[Nicole]

i just bought a house with a 21 year old furnace. i have buyers warranty and am trying to get them to replace it but all they can do is conduct a "certified inspection" to check for cracks and carbon monoxide. the problem is the fee for this is almost $300. does anyone know if i can just use a plug-in carbon monoxide detector in the furnace room to or does this need to be more technical?