New duct work for garage...............

[Bigearl67]

So I am building my dream garage and I need to run the heating duct work. I know practically nothing about HVAC so am relying on some help from my fellow members. I will actually be putting a propane furnace in the old garage eventually which the new garage is attached to and the run will go straight out of the furnace to the duct work. Pardon the dumb questions, but would the insulated flexible ducting be the way to go on this? It sure looks easy enough for me. Does it matter what diameter and how many vents (2 vs. 4)? I built the shop with 2x6 walls and plan to use the blown in insulation in the attic with R 19 in the walls. All help would be appreciated. Thanks, Earl.

[paul52446m]

So I am building my dream garage and I need to run the heating duct work. I know practically nothing about HVAC so am relying on some help from my fellow members. I will actually be putting a propane furnace in the old garage eventually which the new garage is attached to and the run will go straight out of the furnace to the duct work. Pardon the dumb questions, but would the insulated flexible ducting be the way to go on this? It sure looks easy enough for me. Does it matter what diameter and how many vents (2 vs. 4)? I built the shop with 2x6 walls and plan to use the blown in insulation in the attic with R 19 in the walls. All help would be appreciated. Thanks, Earl.

You are asking questions that is hard to answer with out more info.We size ducts to the size of the furnace and the CFM. of the blower in that furnace.
Then we size the opening and amount of opening to get the air flow we want.
You can use flex duct as long as it is sized right. I would need furnace specs.
and diagram of room size to help you lay it out. Later Paul paulm989@lotmail.com Later Paul

[Bigearl67]

Paul, thanks for the reply. The new garage (actually a small machine shop) is pretty much just a 23x27 interior building and I want to run the ducts now so I can install the furnace when more funds become available. This project has become a bit of a money pit. I most assuredly will get a used furnace from Craigslist and am looking between 30,000 and 38,000 BTU. Currently I have a nice open attic with a lot of elbow room to work in and I want nice balanced warmth in this room. I will also have two 52 ceiling fans spinning most of the time. I tried to post pic's but the site would not let me. Thanks again, Earl.

[paul52446m]

Paul, thanks for the reply. The new garage (actually a small machine shop) is pretty much just a 23x27 interior building and I want to run the ducts now so I can install the furnace when more funds become available. This project has become a bit of a money pit. I most assuredly will get a used furnace from Craigslist and am looking between 30,000 and 38,000 BTU. Currently I have a nice open attic with a lot of elbow room to work in and I want nice balanced warmth in this room. I will also have two 52 ceiling fans spinning most of the time. I tried to post pic's but the site would not let me. Thanks again, Earl.

Hi Earl Paul here, First, one 52" fan will do the job very well. The average small 40,000 to 60,000 btu. furnace has a blower CFM. of 600 to 800. So if you are running 6" pipe you would need 6 runs. If you want 3 opening, they would have to be 8" pipe. In a room that size you can put a furnace on one wall and a plenum going up to the ceiling. two or three reg. the right size and they will blow all the way across the room, only if you have a clear shot for them to blow. If you wanted to spend the money you could to a home depot
and buy a garage heater. They mount up close to the ceiling so they don't use up floor space. My private email in the last post way so you could me pic. or drawing if you want. Later Paul

[Bigearl67]

Paul, this is exactly the advice I was hoping to get. I realize one fan would be fine but I like two so where ever I will be working I can feel the breeze. Besides, it’s nice to get to install something in a nice clean attic with new electrics and no insulation for a change. I am spending the day finishing the ceiling dry wall then will be cutting holes for the vents and runs in the next couple days so your advice is timely. This ceiling will be a mess with 11 drop air lines, four ceiling speakers, gantry, and a couple dozen lights. All waiting on the heating info first. I will use just one run, with 8” insulated flex and three large registers ran down the center of the ceiling. Does this sound about right to you? Thanks a bunch for the info, you have been a blessing. Earl.

[paul52446m]

Paul, this is exactly the advice I was hoping to get. I realize one fan would be fine but I like two so where ever I will be working I can feel the breeze. Besides, it’s nice to get to install something in a nice clean attic with new electrics and no insulation for a change. I am spending the day finishing the ceiling dry wall then will be cutting holes for the vents and runs in the next couple days so your advice is timely. This ceiling will be a mess with 11 drop air lines, four ceiling speakers, gantry, and a couple dozen lights. All waiting on the heating info first. I will use just one run, with 8” insulated flex and three large registers ran down the center of the ceiling. Does this sound about right to you? Thanks a bunch for the info, you have been a blessing. Earl.

The average small 40,000 to 60,000 btu. furnace has a blower CFM. of 600 to 800. So if you are running 6" pipe you would need 6 runs. If you want 3 opening, they would have to be 8" pipe. This means you will need 3= 8" round ceiling diffuser and a 8" pipe going from the plenum to each diffuser. One 8" round pipe for each diffuser. Under normal static duct pressure, a 8" pipe will
move about 225 cfm of air, three 8" pipes will move about 675 cfm of air.
later paul