Cold water unit can be used on residential - houses, decks, fence.
Can use cold unit on concrete with good quality chemicals - but nothing replaces a hot unit on concrete.
Houses are normally bid by the liner foot approx. $1 for one story and $2 for two story -- with that said, I just look at the home and give a price - the average ranch home in this area gets about $165 - takes approx 2hrs
Decks can be bid by sqft ($1.00 to $2.00 a sqft). Rails can be done by liner foot or sqft - Spindles and rails take a lot more time than the floor, etc. I have my sealant cost separate from my bid - I sell the sealant to the owner at cost - some wood will take more than other - if more than I figured, the owner has to buy more - all of this is word by word in the contract.
A cold unit 2000psi 2.2 gallon per minute is just fine for decks (wood restoration). WITH RIGHT SIZE TIP
I suggest a 3000 psi 4.0 gpm for concrete and homes.
I know there are bigger and better! For just starting out this is fine.
If your going to do siding - you may want to read about the xjet.
email me for any help on the actual business (books, advertise, etc) part if you like and I will be glad to help you.