Also known astodphodrenovationalteration
After demolition or the removal of a defect, a short Vastu pooja is done even when a full one is not possible: offer 45 small pieces of gud to the 45 devtas, or at least invoke the nine lords of the directions and the centre with the words Bho [name] Vastu Dev Vastu Shanti Kuru Kuru.
Each direction of the house, and the centre for Brahma
Vastu pooja is the prana pratishtha of a house: just as an idol is not worshipped until its prana pratishtha, a house is established only through Vastu pooja. It is due at fixed stages of construction and again whenever the house is disturbed.
A bhatti (furnace) that has been in the ground of a house should be closed only after digging out and throwing away the soil all around it.
Furnace in the ground of the house
Yes, advise removing it: the North is Kuber's place, and keeping filth at the place of wealth is like putting dirt in the mouth, so wealth cannot grow. After any demolition do a Vastu pooja; even a short one is enough, offering 45 small pieces of gud to the 45 devtas or invoking the nine lords with Bho Indra Vastu Dev Vastu Shanti Kuru Kuru and so on for each direction, with Brahma at the centre.
No. Do it at bhoomi poojan or shilanyas, when the first slab is laid, when the main door frame is installed and on griha pravesh; the start of construction and griha pravesh are essential. Also do it after a renovation in which walls are broken, for a marriage, the start of a job or business and the birth of a child, and once a year on a swayam siddh muhurta such as Akha Teej or Gudi Padwa for a year of happiness and peace.