Home inspection for two furnaces today. Changed customer supplied air filter in crawlspace. Upstairs was clean and did not need replacement. Thermostats were found to be not working correctly. Customer approved replacement for both thermostats. Upstairs attic is spray foam with an 80% furnace. Spray foam is touching flue pipe And there is no ventilation into attic for furnace to operate safely. Crawlspace has an 80% horizontally mounted furnace as well and this furnace is venting into the chimney stack. This is not proper to code and also a potential hazard as it can bring carbon monoxide gas into home. Replacement of furnace to a 90% furnace with a new pvc flu with a concentric kit would be needed. Based on our findings today, it might be time to think about getting a brand new system.