Adding heat ducts existing house

I live in a cold climate and I have just added a small addition to my two story home and would like to condition this space by adding HVAC ducts as needed. The new room is 12 x 14 it is off the existing house and is only a second floor additon (no conditioned space below). The room is designed with 2 x 6 walls and a TJI floor system leaving me a 12" space below to properly insulate. What is the best way to run the ducts to this space and how many are needed as well as do I need to provide a cold air return in this space as well? The options I have as I see it are remove recently installed drywall from ceiling from lower adjacent room and install duct(s) through lower floor ceiling and out into addition through the floor. Or I can install ceiling vents by running a duct from the mechanical room up and through the exterior wall (2 stories up) and into attic and then across to new addition ceiling (or run down wall to floor level). Or should I consider an alternative heat source for this area? If I go through the wall I would have to cut out the wall plates (top and lower sill plates) is this acceptable? I am looking for any opinons and welcome all solutions.

Thanks,
Jeff

 

The shorter the duct runs the better. Longer duct runs, and duct runs with lots of turns cause more "drag" on the airflow than shorter, straighter runs. This results in less airflow getting to the desired room.

Another thing you need to consider though is your hvac system's capacity. Adding a 12x14 room isn't a lot of new volume to heat and cool, but if your existing system is pretty much maxed out already just adding this new room to the load probably won't give you the results you hope for. So, you need to do a new load calculation on the system to see how well your system will handle the new load. Read the post below. It discusses load calculations.

http://forum.doityourself.com/showthread.php?t=271310


It's good that the walls are 2x6 (allowing more insulation). However, if you run the duct between your floor joists how are you going to adequately insulate that cavity and the duct that runs in it.

 

Hi N74TG,

Thanks for the reply. It sounds like the best solution is to keep the runs short and as straight as possible and that would mean a straight shot from furnace room through ceiling and into the additions floor joist. As far as insulating the floor bays as you mentioned I am open for suggestions. I will be blowing insulation into all wall, attic and floor space, however maybe I should drop the floor framing level down...say maybe another six inches or more to assure a good insulation job? How about the pipes themselves should I just use a standard pipe or do I have the option of an insulated pipe?
I will check the load calculator link also and make the determination as suggested.
Thanks again,
Jeff

 

Yes, you want insulated duct material. It is available. Don't just blow in loose insulation material around non-insulated duct metal. That could lead to disaster if warm or hot air ever gets to the duct in summer when ac is on (causes condensation, which will soak the insulation and create a really big mess).

I don't remember if you said in original post that you had ac. If you don't and duct will be used only for heating, then you might get by without the already insulated duct material. But, still you'll need to insulate the joist bay.

 

Yes the house is air conditioned also. It was suggested to me also to not only use a blown in insulation but at every bay that has a duct to install a pink or blue insulation board at the bottom of the enclosure and leave room to blow the insulation in on top of the insulator board and around the duct.
I figure I will need to install three heat/AC ducts (one on each wall of windows) and then a cold air return on the existing house wall. Sound about right?

Thanks,
Jeff

 

If you live in my area and need added or re-routed ductwork in an old house, then you will have to do it yourself. Iv'e contacted all the heating/cooling contracters who specialize in ductwork and none of them want anything to do with an old 100 year old house. I think they are making good steady money on just installing and replacing excisting units or doing new constuction. Old houses that were built before the furnace, car, electric lights, radio and tv were invented are a royal pain to work on. The funny thing is that I'm willing to pay what it takes to get the job done and I know it will be costly. I get paid very well for what I do and I in turn I think it's only right to pay people fair.