Hi General Contractors, especially HVAC contractors,
I am renovating and making an existing basement apartment a legal apartment as a second unit. Do I need one furnace or two?
We will have one thermostat on main floor and will be controlled by main floor. I am told by consultant that we need a second furnace as per code. I am surprised. Why? It's a small bungalow. 850 sft on main floor and smaller unit in basement. The total required capacity is less then 40000 BTU, so why I am told I need a second unit?
Can anyone give more light on this topic?
You do not need to install two furnaces in your house to have a legal basement apartment. The issue that is arising is based from a fire separation stance. You cannot have to two units directly connected and open to each other through cold air returns and heating vents.
You have two options: either install a second heating source, or make your current furnace fire safe.
The first option involves installing either a new furnace and distribution system (very costly), installing baseboard heaters throughout the basement apartment and blocking off or removing the current HVAC system, or any other source of heating (radiator, in floor heating, etc.)
The second option would involve installing a smoke detector inside cold air return before the furnace connected to a kill switch attached to both the fuel supply and electrical supply of the furnace. This is the least invasive project but it is also a costly one and requires an HVAC specialist that may not be available in all areas.
Most customers choose to go with the baseboard heater options because of cost and practicality.
Best of luck with your project.
Georgian Custom Renovations
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