Today I came to Trevor and Tanya’s Fairview home becuase the furnace is not working properly. Trevor explained that a friend of his in hvac replaced the furnace 3 weeks ago and it has not been working right since then. Trevor says the furnace works but never reaches temperature on the thermostat. He replaced the thermostat and the problem remained. Upon diagnostic of the single stage 80000 btu builder grave furnace w I found it was installed incorrectly and is over sized for the home. There was also no permit pulled with the city of Calgary as the inspection would have failed due to an over sized chimney. The furnace is 80000 btus when a 60000 BTU unit was required. This can cause over heating and short cycling. The gas pressure at the gas valve was never checked nor adjusted after installation. It was way too high causing the furnace to over heat. While the manual does state that 2” venting is allowed, 3” venting is preferred on anything 80000 btus and above especially with multiple