Performing Energy Audits on residential homes I have come across all kinds for problems related to drafts. There are many reasons a particular room, spot, or floor feels drafty. One of the most come problems I run into now adays kind of goes like this. I get the call " My brand new home is drafty and the builder has tried alot of things but nothing seems to work". The first thing I ask is about the heating system. Do you have forced hot air? Yes. 90 percent of the time I can tell them what the problem is before I even get to the house. Obviously, as I mentioned before there are many causes of the drafty feeling the home owners get.
The one problem I am consistently running into is the design of the distribution system in forced hot air homes. First of all the exact same home with forced hot air is up to 5 times leakier when the system is running. This is because of pressure differences created by the blower. Air is being drawn in and pushed out of spaces that it normally wouldn't be if you had say baseboard heating. On the second floor the builders always seem to install the supplies in the ceiling. In New England this is fine for distributing cooler air during the summer but it doesn't work during the heating season. Look at a window for example. Everyone knows windows are a weak link in the building envelope. Even the best windows allow more heat loss through them than a standard insulated wall. So as heat is lost through the window the air on the inside is cooled and drops down to the floor. For this reason we install supply vents and baseboard radiators under windows to warm that air back up. Since the supplies are now in the ceiling on the second floor they just can't mix the air in the room sufficiently to make it fell comfortable. The room becomes stratified. With the infrared camera you can see it easily. I have been in new homes that there is a 15 -20 degree difference between the floor level and the ceiling. To make matters worse I usually see one return in the hallway. And where do you think they put it. In the ceiling. So which air is being drawn back to the handler to be conditioned? The warmest air in the room. Doesn't sound very efficient does it. Every once in a while I come across a home that went one step further. They have returns in every room but again they are still in the ceiling.
The draft complaints are usually related to the stairs or if there is a hallway that leads to a nice balcony over looking a living room. When you think of the air as a fluid, imagine it as water. The cooler air is denser and heavier at the floor. When the doors are open in the rooms up stairs it rolls out into the hall and down the stairs. Or if you have a nice overlooking balcony it pours over that and drops to the first floor below. On the first floor the supplies and returns are located in the floors. So what ends up happening is your basement system (if you have two) is reconditioning the cooler air from the first floor and the second.
What to do? Homes with baseboard heating or supplies and returns in the floors don't have the same problems. Ideally what you should have is the supplies in the floor just like they are in the first floor. Problem is this would have taken more planning to run the ducts and would have cost more. So the builders choose the easy way, from above. For New England an ideal system would be to have both high and low returns in every room. During the summer the lower returns are closed so the the warmest air in the room can be drawn back to be cooled. During the winter the high returns are closed and the cooler air along the floor is drawn back to be heated. This would make the room feel more comfortable and also make the system operate more efficiently. Again there is more dollars associated with this type of installation up front but the payoff is comfort and efficiency. If explained to a client up front almost all would opt to have the added expense during building if it makes the system operate better later.
Related to this topic is the fact I see builders try to address this by adding the supply in the floors on the second level. But in doing so they run the ducts inside the exterior walls. This causes another set of problems. Obviously you can't get much insulation around those ducts inside a standard wall cavity. I have even seen the stud bay used as the duct. Regardless, what happens is moisture related damage occurs from condensation. Paint peels on the outside, the sheathing develops mold and things get worse from there.
The point is if you are working with a builder pay close attention to the details and how the system as a whole is going to be installed. Common sense is a great thing and is often over looked. If it doesn't sound or look right it probably isn't. It is easier to address these issues prior to framing than a year later after you have been in the home and realize it just doesn't feel comfortable.
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