I need to run some ductwork into basement space that I’m finishing. The ceiling is still wide open. Although I think the furnace is a bit too small, I want to run the new ductwork and see how it goes – then decide on a new furnace before it gets cold again next year. I need to get the ducts run, however, so I can drywall the ceiling and the walls. Can I do something as simple as mirror the ducts that serve the rooms directly over the basement by just running new ducts off of the main line that runs the length of the basement and pointing the new registers down, or is there much more to it that I should leave to a pro?
Thanks for any help.
Replies
There are folks on this forum with more specific knowledge than me, but I would say you need to consult with a knowlegeable HVAC tech. There is more to getting warmed or condition air transfered than just running ductwork. Undersized or oversized ducting, type of ducting, quantity and cumulative angles of bends, location of registers, the cfm capacity of your fan...all can affect performance of your heat system very significantly.
Running the ductwork can be quite simple and straightforward oftentimes, but, without a proper design, you can very well end up losing in heating costs much more than you save by cobbling together some off-the-shelf components that are a mismatch with your overall system.
Jules Quaver for President 2004
Area determines air requirements determines register(s) size(s) determines duct(s) size(s) determines furnace.
This is just one of those deals where you have to think it through from the end and work backwards.
If you're not a pro you might want to at least pay one to help you figure out the math and tell you how to proceed. Don't rely on Home Center advice on this one.
Good Luck !
Simply, YES, just install a mirror image.
You can later balance the system by dampers, so it would be convienient for you to install those in each duct (from experience, your kids will mess up any outlet damper settings you try to establish) when you do the "mirror -per your terminology-" ducting.
One of my first aerospace jobs 36 years ago was to calculate airflow to electrical equipment bays on 707 and 727 aircraft. In the '60's it was done by trial and error, which is probably the easiest way to do it for your house ( TBC switched to an IBM 6020 computer program in 1968) . Alternately, get ahold of a demo airfolw web program and figure how to scale it for your house (hint, the trial and error for your house will be less work overall)
Edit - added "just install a mirror image", since original reply was ambiguous as question was phrased.
Edited 1/28/2003 1:46:37 AM ET by JUNKHOUND
Check out an HVAC textbook from your library. The factors are how many CFM's your blower delivers, and what the pressure drop of the system is. i.e. if you do a bend in your ductwork, like a 90, that creates resistance to the airflow (measured in inches of water column) and will lower the volume of air moved by the furnace blower. Map your whole system and calculate the pressure loss through the existing. Then draw out what you want to do and calculate that scenario. The textbook will explain what creates pressure drop so you have a guideline to designing a good system.
remodeler
Thanks to all for the advice. It looks as if I'll have a few companies come tell me what they think. Perhaps I'll just have someone design the duct system now and deal with replacing the furnace next season.
HD has some 11x17 sheets of paper that cover the ducts and their cfm service based on std furnace output. Beyond that there is a slipstick (sold for 5-10 bucks at HD) that can help you determine the cfm of each main duct leading from your furnace.
To do it right you need to have a balanced system that flows freely. You can half a-- the ductwork system and damper down the flows where it is too strong so the weak areas get some heat but you are working at cross purposes.
In the simplest sense figure out the cross section of the ducts 10X20 =200 sq inches. In a friction free world all you can supply is 200 square inches of heat openings. Anything more won't be serviced by air flow.
In reality the longer the pipe the less there is of the 200 square inches to spread around. Corners and smaller cross-sectional pipes have more resistance as well.
Cold air returns are important too. You have to pull the air as well as push it. In the basement you should install a CAR so the air destratifies any heat you supply to the basement finished area.