Before embarking on a furnace retrofit, it is important for the contractor to consider several items that will more generally influence the viability of the installation.

Firstly, thought should be given to codes, regulations, and permits in the local jurisdiction to ensure that health and safety considerations are addressed. Refer to B149.1 Natural Gas and Propane Installation Code, BC Building Code, and the BC Safety Authority⁴ for further information on health and safety regulations related to furnace installations. Worksafe BC regulated issues such as asbestos abatement can prevent a furnace installation from occurring if not mitigated beforehand and should also be reviewed.

Secondly, consideration should be given to the mechanical room layout/spacing and existing equipment as this may affect the viability of the furnace retrofit. In particular, some combustion appliances may be dependent on the existing furnace system for venting. These can include hot water tanks and other equipment related to the home HVAC system. In this case, hot water tank venting must be evaluated after the new furnace is installed to determine whether venting changes are required to accommodate an 'orphaned' domestic hot water tank.

Note that different furnace configurations will require subtle differences when it comes to installation, venting, draining, ducting, commissioning, and servicing. See below for typical furnace configuration options: