Going against conventional wisdom, I suggest that you don't deversefy too much. My experience is that you end up being inefficient. I've "done" all three.
Duct cleaning - to do right costs a lot to get into it. Forget ram air and roto vac - lame.
Rugs - to do right takes a good deal of knowledge and space.
VCT - low wages and typically done at night. It can rob your energy for more profitable ventures. But it is fairly cheap to get into. And likely you won't ruin anything. I did this for years. It paid the bills, but I wouldn't do it again unless I really had to.
Have you tried diversifying in to commercial? Likely you already have what you need.[/quote
That would be my thoughts EXACTLY. Especially two years into your enterprise, I would focus on doing a better job at marketing your core competency. If you already do Tile & grout, upholstery and carpet I would add small to medium sized water damage jobs if you must add something. Oriental & area rugs would be next but that will require some training and serious capital investment. You could start with a few water damage jobs with say maybe 12 air movers & a couple of Dehumidifiers.
If I had it to do over I would never have gotten into airduct cleaning, water damage work or in house rug cleaning. There is plenty of money in carpet cleaning to make a great living in about 9 months out of the year, without getting stretched out into a billion different services ALL OF WHICH HAVE TO BE MARKETED.
Despite what all the equipment sellers will tell you, there is just as much margin in carpet & upholstery cleaning (operated right) as there is in all ancillary services that this industry works so hard to sell you on getting into with classes, seminars etc.
Be carefully about diversification.
If you are looking for a way to generate more revenue during the off season, I would get a part time job 3-4 days a week during the winter until your carpet business is throwing off enough cash to bankroll your life without doing much during the winter. Then you will not have more money tied up in equipment for all these ancillary services.