TMB – Plumbing Engineer
U.S. factory shipments of gas-fired, warm-air furnaces in April totaled 125000, an 8.5 percent drop compared with the same month a year ago. See chart. For the year-to-date, gas furnace shipments totaled 543338, an 18.3 percent drop …

Science project idea on how houses are heated
How houses are heated by hot air. A hot air furnace is essentially a large stove around which is a metal jacket through which the air passes to be heated. What causes the air to pass through the pipes into the rooms above? …