How about an RGF or REME unit ?

Here is a link that might be useful: http://rgf.com/

I know people who have put pans of vinegar on the registers if they are in the floor so it slowly evaporates. I don't care about the smell of vinegar but it does work to neutralize the odors.

One other and faster option is called Ozium. Wal-mart and some auto parts stores carry it. The original scent is the only one that works well with bad odors so don't bother with any other scents. I will warn you it is overpowering but dies down to a clean tolerable scent.

Turn the heat/air off and FAN on and spray in the air return and give the filter a good spritzing. The rest I would spray the carpet lightly and spray the walls around the windows especially if the previous owners had drapes which are magnets for smoke and hold it close so it permeates the walls.

I would do a combination ozium and vinegar attack. Eventually you will win the war.

I used to work at a dealership years ago that used a small bottle of ozium on smokers trade ins and sprayed under the seat, the headliner under the visors and in the vents and after the can was all gone shut the car and leave it for 24 hours. One treatment on a hot summer day would pretty much eat any odor.

Here is a link that might be useful: Ozium ORIGINAL scent only

Since you both have an immediate odor issue, and ongoing asthma, consider a filter and light system for on your HVAC system. These have a filter that goes in the ductwork where you current furnace filter is, ( the filter rack may need to be changed) and then a light that goes in the ductwork as the air leaves the furnace area.

Here is a link that might be useful: Ultravation.