Ductwork – finishing basement questions
I’d like some advice on HVAC ducting … all the work I have done in the past has been on old homes with radiator heat…first time dealing with forced air.
I am finishing a walkout basement in a newer (99) home. Basement is currently unfinished, but framed, and the finished part will be about 1900 sq. ft. (the finished part of the home is about 3200 sq. ft.) Home is a two story, and is in Minnesota. Systems were sized to handle a finished basement, but the ductwork has not yet been run.
All the ductwork is rigid steel…two larger trunk lines (right term?) extend along under the joists to supply all the branch lines headed out to the first floor registers. The plan is to tap into these to supply the basement, and I think I have my hands around general sizing and placement requirements.
Two questions:
1- Is this a situation where flexible ductwork might be appropriate? I’ve seen mixed reviews on it. My inclination is no, but it would clearly be easier.
2- I have been getting some conflicting advice on placement of the registers. I’ve heard in the ceiling (probably easiest); Close to the floor (heat rises); and even had two vents per run (one up high and the other down low) suggested (top one open, bottom closed = summer, vice versa during winter).
Thanks for any advice!
Replies
Snsteury,
I am no HVAC guy, so take this for what it is worth, but I have finished alot of basements.
I am in Colorado, and the heat/cool distribution ducts tap into the plenum (main trunk) and stay in the joist bays and discharge at ceiling height. And no I wouldn't use flex duct, stick with rigid. Also, try to tap into the plenum on top so as not to lose any more headroom and create additional soffit framing and drywall etc.
The key is to make sure you have properly placed return air ducts that are sized properly. These should be close to the floor, typically use the drywall from two stud bays as the front and back of the return duct, and cut a hole in drywall for register to screw on. This should create a "flow" of warm/cool air from ceiling to floor.
Just make sure you tap into the right side of the plenum for the distribution ductwork.
Hope this helps.
Cole
Cole Dean
Dean Contracting
Thanks for the tips.
If there are any more words of wisdom...I'm all ears.
Personally I would not accept a basement without heating vents and more important RETURN vents at floor level.
Double that with a wallout.
And if it is going to be use for low activity purposes (bedroom, theather) then I would double it again.
Cole (or anyone else, for that matter)-
One more question for you, since you have a lot of basement finishing experience...
The last basement I finished ended up beautifully, but there was a great deal of noise transmission between the ground level floor, which was hardwood, and the basement. That was a 100 year old home, and the rock was attached right to the 2x10 joists. No insulation.
I am worried about the same thing on this project...I have maple floors on the main level, and the joists are 12" I-joists.
Have you done anything special to mitigate sound issues? Insulation? Extra sheetrock, etc?
Thanks again, Steve
On the basement we did last year, we used R-11 insulation between the trusses and used 7/8 hat channel screwed to the bottom of the trusses. We hung the sheetrock from the hat channel. This helps to isolate the rock from the wood framing. It actually seemed to work very well. There is also a special sound deadening metal furring available, but the hat channel is ussually easier to find.
Doug-
Nice to know that it is possible to reduce the noise! I will look into those channels.
What thickness sheetrock did you use?
Steve
I used 5/8 rock on the ceiling and 1/2" on the walls. This was a duplex I built with one apartment in the basement and one on the main level, so I was required to have a 1 hour fire rated ceiling. I don't know if the 5/8 rock has any sound deadening effect or not, but it definitly seems to make a better ceiling.
Bill-
The returns would most certainly be at floor level. The real question is the register placement....when you say "double up", do you mean go with a high/low configuration, or just double the number of them???
The rooms down there will be a rec room, a guest bedroom, bathroom and a home theater.
In somewhat good news...it's been -5 to -10 recently and the slab floor/poured wall basement is only about 8 degrees colder than the rest of the house, without any heating system other than what is supplying the upstairs.
Doug, thanks for the insights on the ceiling.
Steve
Sorry, but double up my ment that my resolve to have a GOOD HVAC would increase that much. Not mean that you needed to double up the ducts.
Now I have my real bias on this. I living on a lake where the ground slopes from the road down to the water. House have been build over that last 70 years. Many of them started out as cabin that have been added on an remodeled many times. But some of them where "conventional" homes with "basements" that at ground level on the lake side and too many of them where cold.
My house is two stores on slab with the first floor living room, dining room, and kitchen. The lakeside front of the house and 1/2 of each side are at ground level with conventional framing and lots of glass on the lake side. But all HVAC contractors that looked at the plans said what they would do for the 2nd floor and then "we will stick a couple of vents in the ceiling for the 'basement'".
After talking to about 10 I found one that would install a separate system with underslab ducts for the supply registers.
The fact that you are having floor level returns might be enough I am really not sure.
It is interesting that it is typical that in these discussion that only the supply vents are mentioned and returns are just as important.
But that really brings up another question. Do you have enough ducts? Has anyone done any sizing calculations as the number and placement?
Bill-
A pro did put together a plan, although I got the sense he was just "doing what they always do" for walkout basements. I was not totally comfortable with him or the "normal" recommendations he was making...
He planned: One return/room, and one to four registers (6" round metal duct supplying each) per room. All Registers in the ceiling, returns at floor level. Room sizes: 230sq ft. guest bedroom (1 register, 1 return); guest bathroom 100sq ft (1 register, no return); 150 sq ft (use to be determined; 1 register); 650sq ft rec room (4 registers, 1 return); 450 sq ft home theater (3 registers, 1 return). and some misc. hallways and storage closets to make up the total ~1800-1900 sq ft. Ceiling heights will vary from 8' beneath soffiting to 9' everywhere else, if that matters.
I am not sure what size the returns were going to be... anyway, I thought that the big room might need a second return, and the guest bedroom needs a second register.
Thoughts?
Steve
I really don't have any idea of the sizing/number of the registers.
You can try http://www.hvac-calc.com/main.asp
The HO version is $49, but they have a free demo version. They say that it does duct calculations, but I don't know if it would be using in your case or if you have to design a whole system and then the duct work comes out at the end and what happens if it does not match what you are have?
JLC has had some basic articles on HVAC installation including at least one on duct sizing. Try http://www.jlconline.com and then Research. The back articles are $5.00 each. Also go to FHB and Archives and see if they have anything.