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Wyjeep 11-02-2008 12:08 PM

Finishing basement, had a few questions about ductwork...
I've been living in a new townhome for about 3 months now, I had the basement framed right after moving in and I'm ready to start finishing it out. The home is 1200sqft main level with 9ft ceilings, the basement is 1200 sq ft with 8 ft ceilings. The furnace is a Carrier 58STA090, will this be sufficient to heat the home? I live in laramie county, wyoming. The manifold runs right through the middle of the basement, and my questions are?

Am I able to tap off of existing ductwork used for heating the upstairs to put new vents on? Some of the heating vents are already in place downstairs, I just have to figure out heating for two 12x10 bedrooms, and one 16x16 gream room. The ducts right right over were they need to be, and it would be really easy to just tap right off of them. Would this violate code, or heat sufficiently?

What do I do about cold air returns?

And are there any special tools or fittings that I'll need to get started?

Here are a couple pics, the first one shows a duct that I could tap off of, the next one shows the basement in general. Thanks for your help in advance!

Wyjeep 11-02-2008 12:09 PM

Wow I'm a moron, could I get a moderator to move this thread to HVAC. Sorry guys :(

Marvin Gardens 11-02-2008 12:55 PM

Is the basement heated now?

How warm is it most of the time without vents?

From the pictures I see that it is about half below grade. Is that correct?

I did a little research and it appears that your furnace could handle 2000 sq ft with normal ceilings. I think it is a 90k furnace with 80% efficiency. Didn't have much time to do further research.

Basements almost require less environmental controls. This being said more than likely you could just cut a few holes in the plenum or the main duct and add some adjustable vents. This would allow control of the environment should it get too hot or too cold.

My home is about 2500 sq ft with average ceilings. I have a 90k furnace and have 3 six inch vents in the basement. It is a little cool in the winter (64-66) and does fine in the summer. We keep our home cool at 64 all winter so the basement is not out of line temperature wise.

If you want to add some pipe to get the air into the rooms you will have to do add some ducting to make that happen. In basements they can be a 5-6 inch pipe since basements don't need a lot of environmental control.

Wyjeep 11-02-2008 07:06 PM

The basement is just about 100% below grade, the windows are showing a lot of light in the pictures. The basement is heated now, there are 3 vents set, all of them are directly on the manifold. One in the bathroom, one in the storage/furnace room, and one in the landing area once you walk in. I think I'm going to close off the one in the storage room and put it in the hallway instead. I will be adding in R13 insulation to the walls as well. I don't mind if the basement is a little cool, I just don't want it to be freezing down there, especially in the bedrooms.

The existing ducting (to heat upstairs) runs right over both potential bedrooms, am I able to splice a vent into an existing duct (they look 6"), or do I need a fresh tap off of the manifold for every new vent?

Thanks for your help!

Marvin Gardens 11-02-2008 07:39 PM

Well, a 6 inch pipe is not much to heat anything beyond a moderate bathroom. If you tap into that you will have problems with heating whatever it is going to now.

If you want to take off of that line they I suggest that you replace that with an 8 inch line and Y off that to the rooms. No bigger than a 6 inch off the 8 inch for two rooms and the current room it heats upstairs.

Replace the current pipe at the plenum and go 8 inch till you get to the last room in the basement. Then reduce to a 6 inch and connect to the pipe at the room above. Take your 6 inch off the 8 inch pipe to feed each room. You will have to get an 8x8x6 Y and then an 8x6x6 for the second Y. The last Y will connect to the current 6 inch going up stairs.

If the rooms are bigger than 100-120 sq feet then you should up size the 8 inch to a 9 inch and maybe go with a 7 inch into the rooms. Neither room looks that big in the pictures so I think an 8 inch would do fine.

The key is that the basement is pretty easy to keep at temperature and doesn't need a lot of energy.

Always go from larger to smaller from the furnace. Never from smaller to bigger.

Wear leather gloves when working with this metal unless you don't mind seeing your own blood.

Wyjeep 11-02-2008 08:29 PM

They must of done a poor job then, all the ducts running from the plentum to the vents are 6", no bigger. The bedrooms are both 12x10. I think I have one bedroom solved, I can tap a vent right into the plentum (runs right next to the room. I would need about 5" of rectangular duct to put the vent flush with the drywall, I'm sure I can find something like that. Now I don't know what I want to do, I don't want to end up having to replace all the ducting down stairs that would be a pain. I just have to figure out one bedroom and the great room.

Marvin Gardens 11-02-2008 09:27 PM

Most living rooms of average size would need at least one 8-9" duct but could have 3 6" ducts so just because you have 6" ducts doesn't mean that you are not getting enough warm air. Smaller ducts spread out will give more even heat. If I have the option that is what I do. It's more work and uses more supplies but even temperature is better.

Wyjeep 11-02-2008 10:27 PM

Oh okay. Well I'll need to run at least two to the gream room, and one to the 2nd bedroom. The main floor rests on I-joists, it looks like it will be a pain to tap into the manifold through them, but no project is 100% cake. Thanks for your help!

jogr 11-03-2008 12:02 PM

You'll want to avoid having a single duct directly feed adjacent rooms (side to side or one above the other) because sound will transfer readily through the ductwork. It will be better if you can run each rooms supply separately from a main trunk or the plenum. That way the sound transfer is diminished.

Your pictures appear to show a main trunk line running perpendicular to (and below) the joists and a return line running parallel and between the joists. Individual room supply ducts appear to come off the top of the main trunk and run parallel with and between the joists. Try adding round ductwork off this main line in the same manner to supply the rooms as needed. With luck you can keep the ductwork between the joists and not have to crossover.

Some I joists like you have will allow a fairly substantial round hole to be cut through the web for duct so if you need to do this you can contact the manufacturer and get the specs on where it is ok to cut a hole .and how big of hole is ok.

It would be good to have at least some return air coming from the basement - perhaps you can tap into the return line for a return in the basment greatroom or hallway.

In the ideal world you need to run an analysis to determine what sized ducting you need to supply your rooms. It really might be worthwhile to have an HVAC guy come out and give you a bid to do the work.

stubborn1 11-03-2008 07:10 PM

I would tap any new ductwork directly off of the main trunk and add a damper right off the tap. Having the damper allows you to reduce the airflow in the summer cooling months assuming the basement will be cooler than your upstairs.

Another thing to consider - if your thermostat is located upstairs and you aren't on a zoned system, the basement will probably be a few degrees cooler than the first floor. When I finished my basement a few years ago, I added electric baseboard heaters to supplement the forced air heating. Each room in the basement has it's own controls and makes it much more comfortable. If you have the electrical capacity, it's fairly inexpensive to add.

Wyjeep 11-29-2008 03:48 PM

Okay, I had an HVAC guy come out and he quoted me $2000, I don't see why it's that much. As stated earlier, there is a register tapped right off the plentum to heat the bathroom, and in the main landing area, that is a cold air return in the ceiling. I think I can run the heating ducts, just one 7 or 8 inch duct to each bedroom, and maybe one or two 7 or 8 inch ducts to the greatroom. I'm contemplating on running a duct to the main landing area, it's about 100sq ft, and right next to the hallway.

I haven't insulated the walls yet, but I have the R13 to install, I think once the insulation is up then I'll have a better idea of what I need to run. I'm also concerned with the cold air returns. Right now I only have one in the main landing area. The HVAC guy was discussing of installing a double sided vent (transition?) in the bedrooms, so that the are would circulate into the greatroom and landing and pick up from there.

I kind of got shorted on the cold air, because the return plentum only runs have the width of the basement unlike the supply plentum. The return plentum runs right over the hallway, so I can tap and put a register right above the hallway, and that would leave two returns for a 1200sq/ft basement (only 1050 finished). What do you guys think? We have the basement all wired, and I need to finish this HVAC so I can sheetrock (still lagging on plumbing the bathroom and wetbar :-)) Thanks guys!

Wyjeep 08-25-2009 03:40 PM

This is an older post, but I wanted to update it. I purchased about $300 in materials from Home Depot to get the job done. After scoping out the project I realized it was going to be a pain to tap into the plentum since it was squeezed tight up against 16" OC (9.5" deep) I-joists. I took a few weeks off from the project and ended up meeting a guy who did the job for $275 INCLUDING materials, what a deal. He's worked for a local contractor for about 8 years and needed some money on the side.

We ran two 6" ducts to the great room (14x18), one 6" duct to each bedroom (12x11), and one 6" into the "landing" (10x13). As stated earlier in the thread, I already had one cold air return in the ceiling. He added a cold air return in the floor of the great room about 6"x18" in size. He also ran a 4" vent for bathroom ventilation outside. We haven't had a need to turn on the heat yet, but I'm sure it will work great. If there are any questions please feel free.

satchfan 04-27-2010 09:27 PM

Question about your basement
Hi there,

I am currently finishing my basement as well, and I have a similar setup as yours and am picking up ideas for the duct work. This guy at Lowes told me that I am better off placing the registers close to the floor, since the basement floor tends to be the coldest part and hot air rises. Initially, I was thinking of placing the registers in the ceiling due to ease of pulling the ducts off of the plenum, but this idea has made me think otherwise. My question is, how warm does the basement get with your setup? Would it make a big difference with the registers in the ceiling compared to being close to the floor?


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