If you are that close to a window and like to keep your windows open, do NOT choose a power vent model. They are EXTREMELY LOUD. I would really recommend that you explore potentially shifting the location of the heater to get more clearance from your window. 4' is code, but I personally would want at least 6'.

A little off topic but consider a tankless. I was in a situation where I needed a power vent / direct vent and the tankless was the same cost. I was also able to relocate it 25' closer to the points of use.

From my handyman perspective, one of my customers had a power vent (I forget the mfr) where the fan motor failed. Cheapest quote we could get to have it replaced was over $400 since the motor was no longer sold separately (mfr now sells only the whole assembly). That led the client to decide on a new heater instead since theirs was 8 yrs old. average quotes for power vent were $1500, which is a few hundred more than for standard gas units.

If the water heater vents out a wall below a window in a ranch house, then I deduce the water heater is in the basement. You also mention exhaust drawing conditioned air, so it must be a "finished" basement. This is of no use to the OP, but to us who ponder. Anyway, I've always preferred to vent the stack through the roof, which eliminates the fumes issue.

You have only the hot water in the tank with a power vent if the power fails.

You may want to consider an atmospheric vent style with a flue damper. These heaters can get an efficiency of 0.67 to 0.69. This is as good as some of the powered vent models. They should be much less expensive to install and buy. See this announcement from Rheem.

On venting out the side of the house and fumes I would not worry about it, if you install to code. We have gas furnace that vents out near a window and it is no problem at all. You just have to allow for ice and snow build up below the vent if you live in a freezing winter climate.

Here is a link that might be useful: Rheem Energy Star Phase II Heaters