Catfishman: Mr. Havac gave you some good advice to which I have to add one caveat: How are your return air ducts installed in the basement? In the old days before efficiency became the norm, return air ducts often used the floor support trusses as return passageways. Subfloors of that day were usually 2x6's or 2x8's that the finish floor sat on. The spacing between the subfloor planks always allowed some basement air to flow into the return air ducts. With the filter mounted at the furnace, dust and dirt would still get caught by the filter. With the filter installed on the one return in your living quarters, any dirt coming in between the subfloor boards will still get sucked into the furnace and eventually cause some or all of the problems spelled out here. You could buy some cans of expanding foam and seal up any part of the return air ducting that might draw air from the basement, but anything short of new well sealed return air ducts is marginal at best. Good luck! Fairyprincess

Any "loose air" in the house is going to be attracted to the return ... even if it's coming from a burned piece of turkey in the toaster oven. Is there more than the one return, which smells? I don't think the heat cycle should be that short. I'd look into the fan, which is on the other end of the "return".

Its really a messed up setup. It really cant be opened any larger. I mean it can but a whole new return box would have to be made and a gas line would have to be moved. It's doable but getting someone in here to do it and the extra cost would be quite a bit I assume. Which to have it done right that is the price you pay correct? There are parts that can trimmed out but as far as the 11 x 14 opening that as big as it can go. Like I said it was a horrible install. They hurried so bad that they tested the furnace to see if it worked. Then after they left he sent me a text wanting me to double check the gas line for leaks. I did the soapy water thing and they were leaking. One pipe was so loose I could easily turn it by hand. It's a wonder it didn't blow my house up when they turned on the furnace to test it. That's just the beginning of things that was installed wrong. So even at 11 x 14 it would be worth the trouble to install a 20 x20 filter grill? The 11 x 14 opening will not be a bottleneck even with a 20 x 20?

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.