The reason is simple, it is a lack of insulation!
The first question is: why is there a lack of insulation?
The second question is: how do I fix this?
Energy Savers Insulation explains why below
The answer to the first question is builders rarely insulate the subfloor of the bonus room. They insulate the ceiling of the garage, but leave a void above the insulation and below the floor or the bonus room. Their solution is to run heat ducts into the cavity, commonly referred to as a hot box. This does not work in Alberta’s climate. The temperature inside the cavity will be the same as the temperature outside. The idea with the hotbox is that your furnace will heat this space. However, your furnace runs for approximately two minutes, every 20 minutes or so. Now the air and the metal pipes for the ducts are going to be very cold, so your furnace spends energy just trying to heat the ducts. This is why your heat registers in the bonus room blow cold air for the first minute of the furnace cycle. Once the ducts are warmed up, they will blow warm air, by that time the furnace shuts off as the rest of the house has warmed up. It’s a tremendous waste of energy and never works. The answer I most commonly hear from builders as to why they do this, “it’s the way we’ve always done it”.
So then, how do you fix it? It’s actually fairly simple. If it is a new build and the garage ceiling has not been put up, the subfloor and perimeter of the cavity can be spray foamed. If it is a home already finish then we can offer a process called a blow-in blanket. We remove a small section of the garage ceiling, directly below the bonus room (20”x20”). Once we have access to the cavity we will fill it completely full of chemical free insulation. By removing all the air and space the cold will no longer fill the cavity, your bonus room will be warm and your heating cost will go down!
For more information, contact Energy Savers Insulation.
Also, visit the Energy Savers Insulation Blog for more helpful tips.