Why do you suspect the patio door? Is your HVAC running when you notice the odor?

Are you willing to perform a smoke test?

The HVAC wasn't actively running at the time I could smell the fumes and there are no other openings to the outside in that room. Also, wouldn't the HVAC recirculate inside air rather than pull outside air anyways? There is an air intake with the furnace filter in an interior hallway.

I don't know how to do a smoke test. I would need to find someone who does that.

Something is creating negative air pressure inside of “that room”. Are you familiar with using tissue or similar to visualize air flow, or do you have or want to obtain an air flow meter ?

How close are these leaf blowers to your door?

Sometimes in pest control, it is easier to remove the reason for the pests than it is to remove the pests, i.e., are they blowing leaves you could rake?

The leaves are being blown off my property on the other side of the fence at least 20 feet from my window, yet I still get very noticeable exhaust fumes in the room.

If there was a major air leak, I would feel a cold draft coming from the door, but I don't. There is still some kind of leak that's enough for me to smell fumes though.

Not sure if caulking would help or if fumes could be leaking in the space between where the two doors slide between each other.

Instead of caulking, are you familiar with “pillows” used to prevent air flow from doors? Or, before purchasing pillows, would you be able to use rolled up towels?

What you are describing as a “leak”, is negative air pressure, the pressure outside the home is greater than the pressure outside.

Open a window on the other side of the house?

Can't open any windows when the outside temperature is cold or hot. It's December now.

Unless there was an exhaust fan running (there was not), I don't know why there would be negative pressure inside the house.

To get positive pressure, the HVAC would have to pull air from the outside and, in that case, it would be sucking in the exhaust fumes and blowing it around the entire house anyway.

No exhaust fans or dryers were running at the time. No fireplaces were on, the water heater isn't inside the house etc..

It's not my property being cleaned with gas leaf blowers. It's a landscape crew on the other side of the fence outside cleaning the streets and common areas of the community.

That's all I have. You're on your own.

Sliding glass door, perhaps the vertical is comprised? Just enough for the gas fumes to get in?

I would try Leak/flow testing: instruments or tissue. Can you google?, are you willing to?

Are you more sensitive to hydrocarbons than others? I often smell cigarette smoke before my walking companions.

I’m not more sensitive. However, it’s probably good to be able to smell the 2-stroke engine fumes since carbon monoxide is odorless.

What would I Google?

If there was negative pressure, what can be done about it that doesn’t involve letting in cold air in winter or hot air in summer and wasting a lot of energy?

Be glad you can smell it please. Carbon monoxide, the gas that kills ya, is odorless.

If there was negative pressure, what can be done about it that doesn’t involve letting in cold air in winter or hot air in summer and wasting a lot of energy?

Find what's moving air inside your home to the outside. Either turn it off, or force it to source its intake from outdoors.

I gave some examples of such air extractors above, but again:

> Replace indirectly vented gas furnace and/or water heater with ones that are directly vented. Note that a power vented appliance, such as a typical 80% gas furnace, isn't necessarily directly vented (and probably isn't). Alternatively, move these appliances to a fully ventilated space, such as the attic. Since you said your water heater is already in the garage, make sure your garage has enough ventilation and/or leakage to provide the WH with sufficient make-up air, or it will draw some of that air from your house anyway.

> Replace conventional exhaust fans with air exchangers (heat recovery ventilators). These exhaust indoor air and immediately bring in a balanced amount of outdoor air, transferring the heat from one to the other as necessary to conserve energy. IIRC, the best of them can recover about 85%.

> Move your clothes dryer to the garage. The above admonition about make-up air applies doubly here, because the dryer shoves a LOT of indoor air outdoors.

> Don't use fireplaces and woodstoves, and make sure their dampers are sealed shut.

Fifty years ago negative pressure wasn't usually a problem, because houses were leaky all over. Any time you ran something that moved air from indoors to outdoors, outdoors quickly sent some of its air right back in, though all those little cracks and crannies under doors and around windows.*

Modern homes are sealed better. That's good for energy conservation and keeping your fuel bills low, but that's also why you have problems with negative pressure now.

This reduction in air leakage also makes your indoor air quality significantly worse than it used to be, because so little fresh air gets in. Particulates stick around. Volatile organics from household chemicals and products of combustion from your gas range (if you have one) hang around in the air longer. If you have a well-sealed house, you really should have heat recovery ventilation for better health anyway.

*This is why older houses are crackly-dry in the winter. You might think that heating dries the air out, and that's sort of true, but it's a little more complicated than that.

Cold outdoor air may be at 50% relative humidity, but the "relative" part in "relative humidity" means "relative to how much water air at that temperature can hold." Cold air just can't hold much water. So if you have an old home like mine, as your furnace and appliances send household air outdoors, that cold air pours in through the many air leaks to replace it. The furnace heats that cold outdoor air up, but it still has the same absolute amount of water in it. So relative to its new higher temperature, its humidity is more like 20%. Cue the annoying kid shuffling his shoes on the carpet and zapping your poor dog's nose. Or yours. :\

Some well-sealed newer houses actually have the opposite problem, too much humidity, in the winter.

Hope this helps.