Performed preventative maintenance for a Lennox furnace model #Ml180uh090p48b-01, serial #5911A16902. Powered the system down and removed the access panels. Removed and cleaned carbon off of the flame sensor, cleaned out the burners and burner box. Replaced the air filter size 12x24x1. Checked all electrical connections to ensure that they are secure and in good condition. Checked to ensure that the pressure switches are free of any debris. Powered the system back up and called for heat. Took a combustion analysis test and got the following readings, o2 is at 11%, and the co levels are at 26ppm. The supply temp is at 134°F. The inducer amp draw is at .78 and the blower motor amp draw is at 6.7. The system is operating properly at this time. The homeowner would like the water pipes in the crawl space insulated. This includes about 25 ft of water pipe. See estimate.