One of the other casualties of the idiocy of up or down venting is the dryer itself. I can't tell you how many people go shopping for a new dryer 2-3 years after they replaced the old one. When you get blocked airflow, you burn out elements. And lots of people don't have a clue as to how to replace an element or clean a duct out. So they just buy a new one and wonder why it still takes 2 hours to dry a load in their new dryer. There used to be several threads on the Laundry Forum showing pics of how badly lint accumulates in such a duct. It IS shocking. I did find a thread that showed how much lint was pulled out of a simple direct to the exterior vent. Something through the roof would have 10 times as much possible lint accumulation. Think about it! Here is a link that might be useful: Lint pics

Dryer booster fans are usually illegal and prohibited from installation under nearly all Residential Building (mechanical) Codes. The 2006 version of the IRC does not approve of their installation under any circumstance. Likewise you will be hard pressed to find a single dryer manufacturer that permits the installation of dryer boosters on any of their products. Likewise, you will find few, if any 'dryer boosters' that have been 3rd party tested, listed and labeled for use. Not even the Fantech dryer boosters listed in the previous post are allowed for use in residential applications in the US. They are not tested nor listed by an approved US testing agency. They are only approved for use in Canada under CSA testing rules not recognized in America. Likewise even Fantech states: "Fan impeller may accumlate lint. Periodic inspection, based upon dryer usage, should be performed to ensure fan impeller is not obstructed or coated with lint." Some dryer booster fan motors bear a UL listing, but that should not be misunderstood that these devices have been approved for use by UL as 'dryer boosters'. UL does not test these devices for their duct performance. The fact that these devices require routine inspection and are located in in areas not easily accessible nor routinely frequented make them extreme fire hazards under all circumstances. Check with your local code office and the dryer manufacturer's installation instructions before allowing your builder and his plumber to install this device. The correct approach is to relocate the laundry area to provide easier direct access for the dryer vent or to run the dryer vent through the roof to stay within the Code or dryer manufacturer's approved run lengths for your make and model dryer. Whenever possible, these devices need to be avoided. They are dangerous since they are normally not approved by anyone to be there.

In the search for an answer to my problems with Bosch dryer, I stumbled upon your problem. Although you said you cleaned the whole system multiple times, I have to ask if you cleaned the compartment underneath the condenser unit? First thing, unplug the dryer. When you pull out the condenser, at the bottom of the tunnel is a hatch door. Underneath that lid is a compartment for water. In case you don’t see it, just push your hand down the tunnel and you will be able to feel it. It can get really messy and green in that compartment underneath that lid. The water pump is located on the left side of the tunnel. Steam goes through the condenser, and water gets in that hidden compartment and the pump pushes the water through the pipe, up in the condensate container. In my Bosch model, these are the parts that get in touch with water. Maybe your smell problem is there. If you are going to clean that part I’ll advise you to take the left panel of the machine off. It is much easier to work like that. Also at the back of the machine, when you take the smaller lid down (the one with a lot of screws, shaped like a foot) you will uncover the motor fan. Underneath the fan, in the plastic that surrounds the fan is a hole. Check that hole because green algae end up in there also. Clean the metal lid because it can get wet and full of lint. Maybe you already have done all of this, in that case maybe this will help someone else.

Megan Morrill-Denton, several people here offering a lot of good points. Since you've cleaned your ducting, I can't think of any other ways to improve drying, and you've mentioned you really don't have any length to the outside except 10" - though if you've got the 'corrugated' type ducting, straight galvanized might help a little. You've also mentioned that the ducting to the dryer isn't kinked... so I've no further help on that other than to suggest you use electric foil tape when you connect it to the dryer - we only had the clamp initially and it did a poor job of holding the duct leak-free to the dryer. You mentioned a cold floor... we had that issue - the whole room actually. When we pulled out our old dryer, I noted cold air flooding from the corrugated duct coming out from the wall (actually placed a baggie over it, taped it close to keep cold air from flooding into the room - the baggie stayed puffed with air until we replaced the outdoor vent cap). I can't really speak for the Heartland style outdoor vent other than to say once we installed that, I noticed the baggie no longer inflated with air from the outside. That was a plus for us. We previously had the slat-style outdoor vent. As dadoes mentioned, it needs painted if you don't want it to stick out like a sore thumb (it's rather big), and I used a can of plastic approved Krylon Fusion paint from Lowe's for ours. Keeping any part of your ducting and vent cap clear of lint is important, and reduces fire hazards - sounds like you are doing this. Good luck on your situation.