Greater Manchester Police said the 79-year-old man was not seriously injured in the attack, which happened at the house in Worsley Mesnes, Wigan, shortly after 7pm on Monday.
Four men, all white and wearing dark clothing, fled the scene on Snowdon Avenue with a quantity of cash, police said.
One of the men was said to have been carrying a screwdriver.
Police also appealed for witnesses to a burglary shortly after 6.30pm on the same day at a house on Bird Street in Ince, Wigan.
A force spokesman said an 89-year-old man answered the door to four men, all white, wearing dark clothing and with Wigan accents, who said they were from the council and were there to check the water supply.
Once inside they stole a number of personal items.
Anyone with information can call 0161 856 7124, quoting incident number 2749 of 14/10/19, or Crimestoppers, anonymously, on 0800 555 111.