My first ac unit I replaced was a Trane that lasted 5yrs according to all the AC Companies in Florida. I went with ahead in Oct 2014 and had another Trand(reck) installed. Six months after installation I started smelling something like wood burning or some irritating chemical. Original company came out and claimed nothing wrong. I had a friend who once worked with ac-units check the unit. Opened all panels and found water in the entire bottom of ac unit. He cleaned all but the fan with exception of blower due to heavy rains. I later had the lite mold removed. Smells continued and I had other AC Companies check unit. All continue to state nothing wrong & no sign of mold. I have had like 3-4 companies check the Trane with different stories. This month April 2018 had a new company check my home for air quality. He found the mold has gotten worse. I paid $2K to have mold cleaned and now also have an electronic air filter. Previously had another company that sold me an $800 purifier and my friend had earlier installed me a UV_Light. None of this has worked. By Friday night, 4/28/18 at 10pm the burning smell started. I had to put a fan in the window to pull the toxins out. I wrote this new company and will be having a visit this coming week to check ac unit again. I worry that I have been living with this harmful condition for over 3-yrs and what health issues are there in my future. I don't trust any of the previous companies and hope this new company finds the problem. As for the mold, if the first company had opened all the panels, they would of found the water and maybe none of this would have happened. I never had problems with the ac-unit until this 2nd Trane was installed. If I ever need to buy another, it won't be a TRANE. It is like this smell lingers in your home to a point you have to open windows. I get sore throats, itchy eyes and nose irritation I use Vicks to help me breath better. Thanks for reading...

Hi - a lot of these posts seem to be slightly different but thought I would share my experience in my home that may prove helpful or be similar. My wife and I moved to our home newly built 5 years ago tomorrow! I can't say I've noticed the smell in the first year but maybe it's poor memory. After the first year, we'd notice this propane/rotten/dead animal like smell. At first I thought the builder put something in the vents - no signs of any rodents ever and ruled this out. Next I checked the line/drain from the AC/furnace and even had a tech check and clean the pump - no help. plumber says there is no issue with drainage or sewer or any back up venting - ok. what HAS helped intermittently is calling the gas company to check the gas lines inside. I've had them 7 times in the past 2 years, each time they find a small leak - nothing major, no reading except with the sniffer right at the source of the leak. {I also have multiple CO and gas detectors on the floor (heavy gas). They have never gone off}. After the gas company repairs the pipe the smell is gone for a few weeks maybe months depending on warm or cold season. It comes back, gas company is back out and repeat. I have replaced two ovens in the kitchen due to them being the source of the leak. I find that the air return on the main level of my house sucks in the smell and returns it to the furnace. When the furnace kicks on we smell it out of the vents. Occasionally I can smell it in the room where the furnace is also. Gas company has done line checks, pressure checks, fixed leaks - I've paid them thousands to come out and fix this over and over then the smell returns - I've returned two "new" ovens due to leaks after minimal use. I have a 2 yr old son and new baby due in a month and NEED this resolved. Please let me know if you have any suggestions or have been through something similar.

" So, how can I get them to explain to me why they recommend a 110?" The contractors who did not do a load calculation will say it is based on the size of the house. This is wrong and leads to over sizing. The one contractor (Sears) who did a load calculation thinks the heating load should be doubled which is also wrong. It is hard to have a conversation about this with a contractor who has already predetermined what size should be installed. "Also, if I do go with the bigger furnace (110k BTU), what exactly am I compromising on? You say bigger is not better. So what exactly is wrong then?" Here is a list of problems caused by an over sized furnace: Short cycling: The furnace runs in short cycles. This constant on and off creates a lot of wear and tear on the furnace and leads to premature failure. It also creates a blast of air every time it turns on causing excessive noise and discomfort. High static pressure: A big furnace needs a lot of air. Your duct work is likely too small to handle the air flow and will cause a restriction. The restriction causes the furnace to run hotter which will overheat the heat exchanger. This will cause the heat exchanger to fail prematurely. This is a very expensive repair. The undersized duct work causing excessive noise. Lower efficiency: During the first 5 - 10 minutes of operation the furnace is operating at a lower efficiency. If it short cycles it does not reach its rated efficiency level. Less Comfort: The short bursts of air blowing at high speeds and the extra noise make the house less comfortable. This is the primary reason forced hot air systems had a bad reputation 20 years. Proper sizing and variable speed furnaces have greatly improved the comfort level. "So, I don't know why you are saying I don't need a 4 ton AC." You don't need a 4 ton AC because you said "Manual J came out to 3.28. " As Tigerdunes stated above you should get either a 3.5 ton single stage or a 4 ton 2-stage condenser. If I knew the city where you lived, and the summer design temperatures used in the calculation, I might be inclined to round down to 3 tons if you lived in an area that suffers from high humidity. I don't know what temperature you set your thermostat to, but I am comfortable at 78 degrees at 40% humidity. I find it more comfortable than 75 degrees at 60% humidity.

Pictures of the system and vent (flue) ductwork would help. Rereading this my first guess is they didnt actually seal the joints. Thinking of a different post recently, it is not common practice for them to think about sealing flue joints but with this pressurized direct vent system they need to, the long horizontal run would be another indication for sealing. Either with furnace cement which requires taking the flue apart and applying while putting it together or using a high temp silicone with it in place. This is the best stuff I could find with good reviews. https://www.amazon.com/Rutland-600-Degree-Silicone-Cartridge-10-3-Ounce/dp/B001GP3AE6/ You do want to seal around the foundation penetration. Critters, insects and cold air can get in. The high temp caulking would work for that as well. Is there anything to protect the vent and intake from touching the foundation wall? It appears you had corrosion there in the past and would probably happen again. If you can get the caulking between the ducts and the foundation that would probably suffice.