This thread http://www.gassavers.org/showthread.php?t=9296
included some discussion of a HAI for a Civic HX. I finally decided I REALLY need HAI or at least WAI as intake temps below about 35-40 degrees F seem to prevent the car from going into lean burn mode.
Well I did it today. Easy to do, once I realized how. Cut openings in bottom and driver's side of air filter box, to let it pull air that's passed through the radiator. Success! Normally the intake air temp (IAT) has been 10-15 degrees above ambient. With the new openings cut and the original tube blocked, temperatures were fully 30 degrees above ambient for highway cruising. The intake temps were very stable too, in spite of hills and all the needed throttle changes. In town with stop and go traffic and errand stops, temps went about 40-50 above ambient.
The usual HAI / WAI method is to run a tube to the exhaust manifold. However that path is crowded on this car, especially if you want to pull air into the original open end of the intake system (I gave up on using the original opening though).
Easy method on this car: Cut openings in the bottom and driver's side of the airbox. In first photo below, yellow oval shows location of original intake port. Green arrows show where I cut openings in filter box. I used a Dremel type grinder (Black and Decker, actually) with a small cutoff wheel.
Openings at green arrows pull in air preheated by the radiator.
This photo shows the locator tabs at front of air box widened by grinder. Pry tab jaws apart with a flat blade and cut away some plastic to be able to get the thing out of the car. Then widen and clean up the cuts a bit once it's free.
Here's a closeup of the cuts I made. I also blocked off the original intake port near fender with duct tape. You can add/remove tape where needed to adjust the amounts of hot/cold air.
Currently getting +/- 50 mpg in fall weather. EPA is 31/39 so not too shabby. WAI, fuel cutoff switch, full belly pan, smooth wheel covers.
This is how I routed mine on my EF with a battery to add to Honda's cramped bays.
Since warm weather is right around the corner I might be interested in doing something similar to what you did since what I have now might be too much heat. But this picture might be somethign to think about if you're looking to add more heat.