Ok, a couple of questions here...

I am finishing off my basement (approx 450 sq feet). I am planning on adding four 6 in. ducts (taking them off from the main trunk) Plus, I am planning on leaving the small vent that is already cut into the main trunk (for a total of 5 vents). I am adding a bathroom and was going to run one of the 4 new vents in there.

I was also planning on cutting into the 'cold air return' and running a 6 in. duct about 4 feet to an interior basement wall for an air return in the basement.

Am I on the right track here or way off base? Also, how can I find out if my furnace/A.C. can handle these new ducts? I don't have any documentation on the furnace/A.C.

One last question. By cutting into the cold air return so near to the furnace/A.C. and running a 6 in. pipe, will I be "sucking" too much air from the basement and not enough from up stairs?

I live in Missouri where the winters are cold and the summers are hot....

Thanks for the help...

 

That is way too many ducts for that. When the furnace is on, you'll bake in the basement and end up shutting most of them off.

I just used the existing duct and my basement is very warm in winter. My bro-in-law added a couple of ducts, but he divided his basement up into 4 rooms.

Best bet - insulate the exterior walls. The savings in my winter fuel bills paid for the insulation in 2 years.

To figure out the ducts needed, contact a heating/AC contractor.

 

Thanks for the response Bob. I was just going by the rule of thumb that said 1 CFM of air is required to heat/cool about 1 sq foot of floor area, and I figured that a 6 in duct would deliver about 110 CFM. 110 CFM * 4 ducts = 440 + the little vent that is already there to make up the difference....I've seen that rule in a couple of places, but I don't know how well it works.

I know that it will be plenty of cool in the summer (It already is now with the 1 vent down there) I was just afraid of it being too cool in the winter without sufficient ducts.....

You said that one works good for you though? Is your basement about the same size?

Thanks,
Preston

 

Actually, my basement is double that (around 900 s.f.) excluding the area left for storage and small workshop. I figured the single vent was sufficient when the house was built and would still be sufficient. My finished area is open - no divider walls. It was cool year round before being finished. The insulation really makes a difference.

Friends have a house where the single vent was sealed up - ie, no heat/AC in their finished basement.

 

I recommend that you install more registers than you think you need. You can always close them if it gets too warm, but you cannot easily add more if it gets too cold. The heat gain/heat loss characteristics of one basement are likely to be very, very different from another basement, based on too many factors to figure.

I have five output registers and one return register in a 800 square foot basement -- I wish I'd installed more. I've been forced to use supplemental electrical heat (thank goodness I installed excess electrical capacity). In my situation, I believe the problem is that I live in a very sunny location. Radiant solar heat does such a good job warming the upstairs where the thermostat is that the furnace doesn't come on enough to adequately heat the basement.

 

Thanks for the response John. A concern I have is that by "overdoing" it on the new ducts I would take away from the upstairs....but I guess by "underdoing" the basement duct work, I would be taking away from the basement....

I did just visit a house under construction (very similiar to mine) where "the pros" were finishing off the basement. They had 4 ducts down there with no cold air return....

I think I'm going to go with the 'more is better' method....

Preston

 

Building code requires a cold air return on each floor. Don't leave it out.

 

Preson,

I am just across the state line in Overland Park. I finished my basement project right at a year ago, it includes around 400 sqft in the finished area, a small 1/2 bath, and shop area. I used the one existing vent and added a second. I also tied into the cold air return. My basement is the most comfortable room in the house and its tempature is also the most consistant. It is that way even with both vents closed and a cover over the return air. Only on the coldest winter days will I open one of the vents.

I recommend having a couple vents but also insulating the walls very well. In addition, do not forget to insulated the rim joist area and the joist next to it. Where the joists run perpendicular to the outside wall, run insulation at least 2' in towards the house. I used a drop ceiling but also bought higher quality ceiling tiles. While I bought the more expensive tiles because of looks, they also have about twice the insulative value as the cheap ones.

I added the second vent because a contractor relative of mine with 40 years experience had recommended it. He only gave me his experience, I still did all the work. Also the exisiting vent was in one corner of the basement, and we felt the other corner might need some coverage. He also pushed me to do the little extras that make the basement much more liveable (plenty of electrical outlets, extra insulation, extra 3 way light switches at both the top & bottom of the stairs, better pad & carpet). Excluding the carpet those extras probably cost only a couple hundred bucks more, but make it so much nicer. Like when the kids leave the lights on, I do not need to go downstairs to turn them off, just flip the 3-way switch at the top of the stairs.

Good luck, keep us informed how it goes.

 

I am almost done with my basement and here in Minnesota the rule is 1 supply and 1 return in every room. The supply is generally centered above a window to prevent fogging in the winter and the return is there for circulation. Bathrooms must have a supply and must not have a return. I guess they figure that the exhaust fan is best to get rid of the moist air. I had to actually change the size of my main feeds and returns so I could move enough air volume to my farthest register.