The HG2 Winter Pack, model HG2KW4, includes all of the accessory head instruments you need to input data automatically into the HVAC Guide® System Analyzer for heating season plus portions of the CheckMe!® test. In addition to the HG2, ATH4, ATA1, and ATWB1 that come standard with the HVAC Guide, the kit includes the combustion heads needed for combustion analysis. The AOX2 Combustion Check head gives measures %O2 and flue temperature, calculates %CO2, and comes with the new AOXP2 flue pump and ATBF1 hi-temp thermocouple. The ACM3 Carbon Monoxide Detector head measures CO ppm in the flue when used with the AOXP2 flue pump. The kit also includes our Large Deluxe Meter Case, model ANC8 to hold it all with room to grow.