"That means he could twist his words after executed the contract with me?" If you were buying a new Honda Accord, would you accept that no specific model number was put on the sales contract (ex. LX, EX, EX-L, 4 or 6 cylinder)? It is the same thing in HVAC equipment. You are paying for a specific size and model for each piece equipment. Perhaps you trust the HVAC contractor to do the right thing, but more often than not it does not happen. If you have low humidity (less than 30%) then you may want to invest in a humidifier, otherwise you don't need.

Thanks for the quick responses! The existing furnace is an oil-fired York, 125 KBTU, which is at least 30 years old. I have been told it's horribly inefficient, but I don't know the number. The AC condenser is 3 tons and 25 years old (also not efficient). The house should probably have 2 zones (especially to deal with better cooling the second floor in the heat of summer), but I have been told that's not possible (at least not for a reasonable price). Otherwise, there are no noticeable issues with the current system, other than those endemic to scorched air heat. Each room has at least one supply vent and one return. The basement is below grade and is used as living area. There are two supply vents and one return in the basement area. There is no insulation between floors, but the basement walls are insulated (R-7.5). Beefing up the attic insulation is on the near-term to do list. The house currently does not have a humidifier, and while no one is suffering nose bleeds, the air is dry. So, I thought a humidifier would be helpful. I would definitely like to tighten the house (and new windows may be on the radar in the near future), but given that it is an older home, I think there is only so much that can be done. The Carrier dealer said the furnace would be no more than 100 KBTU, with the final determination after the house is measured and a load calculation performed. Both companies will also do a whole house energy audit prior to commencing work. So I would assume (and hope) the Lennox dealer will modify his numbers accordingly after the load calculation and energy audit. Our natural gas marginal price/therm is $0.83 Our electricity marginal price/kWh is $0.22 for on peak, and $0.07 for off peak. With regard to the Carrier condenser, what makes the 24ANB6 superior to the 24ACC6? I know a lot of people on this forum prefer Carrier over Lennox. All else equal, I have no problem going with Carrier (I know the Infinity controls are fantastic), but there is a $1,500 price difference... Thanks again for your help.

Thanks... my update should be interesting. Yes the Gas Co did have a reg tag on it that I hadn't seen before. Regardless, I called the Gas Co back for another check. This time a different guy showed up. He could not find any of the issues that the first gas guy found and definitely didn't see any issues that the HVAC company found. The pilot stayed lit, the flame didn't "smother" and he could not find any evidence of cracking. He suggested that we look into a new furnace, however, this one would be fine for now. Go figure! It is an upflow furnace and I do realize that we need one rated for mobile homes. I am definitely going to start looking for a new one, but he said it shouldn't come close to 4500. Since the gas company isn't making to look money off of me, I am more comfortable with their findings than I am with the HVAC company. Thanks for your responses...it's been a very educational day for me.

1. Altitude can effect performance of a furnace. I don't view Bend, Oregon as a really cold climate, so I really don't think this will be a big issue. As long as combustion air is adequate and duct system is designed and installed properly I can't imagine this being much of an issue. 2. Humidifiers are maintenance headaches. If you don't plan to pay to maintain it... it won't work for very long. 3. More maintenance costs. If you fail to do the maintenance on any of these sorts of things it won't work for long. 4. You guessed it, more maintenance costs... more things to break. HRV stands for Heat Recovery Ventilator. I think it can get cold in Bend... but not like Minnesota or Chicago type cold. Really all this is... is a method to take in fresh air from outside and bring it inside without letting a lot of the heat in home escape to the outside. 5. Air scrubber: again if you aren't planning on maintaining it forget about it. You will have to replace UV bulbs annually, even if the bulbs don't burn out in that time. If the model you choose creates ozone in any amount it could give you health problems down the road. It has been determined that ozone in any amount is not good for you. Air scrubber make claims, but provide no proof. They claim they spent a million dollars on tests but provide no proof as to the results of these tests. "If it sounds too good to be true......" If you don't maintain all these systems, it doesn't matter what you pay for them. Whatever the sum it is all wasted money. Don't look at just installation costs. Warranty of ANYTHING, does not include maintenance. In fact without proper maintenance you're more likely to void the warranty.