Not sure if this is horror or a thriller, but it sure sounds intriguing to me:
Crawlspace by Herbert Lieberman, $1.99 at Amazon: Albert and Alice Graves live a normal, if monotonous, domestic life. They’ve never had children; they spend their days tending to their home and enjoying their time together. One day, when the oil man, Richard, is refilling their furnace, Alice invites him to dinner, never suspecting that a casual act of charity will lead to a horrifying, morbid discovery in the crawlspace underneath their beloved house.
It was made into a movie in 1972 (not the Klaus Kinski movie I was thinking of though).