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Old 12-19-2011, 09:02 AM   #1
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Adding an extra vent


Hi folks please forgive me in advance for not knowing much about HVAC & HVAC terminology as I am novice looking to be pointed in the right direction. I am in the midst of a crawl space project which I am insulating and eventually wanting to convert to a conditioned crawl space.

I have plenty of heating/cooling ducts running through this area, one larger then the other four. The four are smaller and they lead directly to the floor vents for the living space above. The one large one (not sure what's the proper name for it) also runs through this area partially. My question for you guys is how hard is it and is it possible for a DIY to add a duct in this area? Could I tap off one of the other ducts running somehow someway? I've read forums where folks drilled holes into their exisitng ducts so it would release conditioned air into the space, but I am not so so sure about that and what the repercussions of that would be, just sounds not right to me.

First picture (for lack of a better word) the main duct which is insulated by the previous owner running through the crawl. Second pic is that of one of the four ducts leading to vents for the above living space coming off the main duct work. Third is just a duct/vent going through the floor. Thanks in advance for any help and or advice. Hopefully there is something DIY I can do
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Old 12-19-2011, 10:10 AM   #2
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Adding an extra vent


Before you do anything, they used the wrong kind of tape on that insulation and it looks like none of the exposed duct work have any tape. It should have been foil tape not duct tape. Duct tape rots and will just fail as you can see it's doing already.
Why is it you think you need an extra line? If it's because the rooms cold, it may be because there's no R19 insultaion in the floor joist bays, or poor windows.

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Old 12-19-2011, 10:14 AM   #3
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Adding an extra vent


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Originally Posted by joecaption View Post
Before you do anything, they used the wrong kind of tape on that insulation and it looks like none of the exposed duct work have any tape. It should have been foil tape not duct tape. Duct tape rots and will just fail as you can see it's doing already.
Why is it you think you need an extra line? If it's because the rooms cold, it may be because there's no R19 insultaion in the floor joist bays, or poor windows.
Thanks Joe! Yes I am fully aware that insulation job is butched. I haven't gotten that far into my project to address it yet, but will. I am in the process of replacing existing R-13 fiberglass with Roxul R-15, but that's another topic over insulation. I want to create a conditioned area in the crawlspace as I am sealing it off. I'd like to achieve this by simply adding a vent or two to the main supply line but want some HVAC advice.
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Old 12-19-2011, 11:08 AM   #4
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Adding an extra vent


If all of the cfm is already used up and I'm betting it is then by tapping into that air you will be doing more harm than good.
What happens when the system is off and there's an opening down there? All that new insulation would mean and account for nothing as you'd simply bring the crawlspace conditon directly into your home via that duct.

I wouln't condition that space, I'd mainly focus on the insulation.
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Old 12-19-2011, 12:22 PM   #5
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Just remember, you not only need to open a vent in the supply but also the return. Be sure to put some dampers on these openings.
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Old 12-19-2011, 12:29 PM   #6
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Originally Posted by Doc Holliday View Post
If all of the cfm is already used up and I'm betting it is then by tapping into that air you will be doing more harm than good.
What happens when the system is off and there's an opening down there? All that new insulation would mean and account for nothing as you'd simply bring the crawlspace conditon directly into your home via that duct.

I wouln't condition that space, I'd mainly focus on the insulation.
The whole crawl space issue is a debatable. There is plenty of resources out there that suggest converting it to a conditioned crawl space if done properly is effective.

To answer your question of "what happensd when the system if off" what happends? The space down there temp wise is similar to the living space above it's treated as a basement. What happens when your basement vents are off? I don't agree with you the insulation would account for nothing. I am insulating the crawl space from the outside elements keep that crawl space warm like a basement. Way off topic just trying to find info about adding a vent. Thanks for the input.
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Old 12-19-2011, 12:30 PM   #7
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Originally Posted by AandPDan View Post
Just remember, you not only need to open a vent in the supply but also the return. Be sure to put some dampers on these openings.
AandP, I am so sorry but that is all greek to me. Return? Dampers? My apologies for not knowing much about HVAC terminology.
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Old 12-19-2011, 12:39 PM   #8
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Adding an extra vent


The supply line is what comes FROM the furnace. It supplies the heated air.

The return goes BACK to the furnace.

If you just open the supply, then you are pressurizing the space and the air won't flow through it. You need a complete path for circulation.

Dampers, they are basically adjustable grills that you can open/close as needed to control the airflow. Like a valve on a water pipe but for air.
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Old 12-19-2011, 12:41 PM   #9
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Originally Posted by AandPDan View Post
The supply line is what comes FROM the furnace. It supplies the heated air.

The return goes BACK to the furnace.

If you just open the supply, then you are pressurizing the space and the air won't flow through it. You need a complete path for circulation.

Dampers, they are basically adjustable grills that you can open/close as needed to control the airflow. Like a valve on a water pipe but for air.
Sounds more complicated then I thought. I thought I could just add in an air duct similar to this web link but down in the crawl space

I do have a return already but I guess your saying I need another return? Always something, lol! Look at Pic two which is an example of a branch line coming off the supply, thought I could just add another one? No?? FUDGE!!!

Last edited by cbaur88; 12-19-2011 at 12:43 PM.
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Old 12-19-2011, 12:49 PM   #10
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You just need an opening in the supply and return. How you do it up to your layout.

You didn't post a link.
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Old 12-19-2011, 12:53 PM   #11
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Originally Posted by AandPDan View Post
You just need an opening in the supply and return. How you do it up to your layout.

You didn't post a link.
Thanks AandP, I think I am outta my league. I know I have two return vents, one i my hallway and one down in my den. I wouldn't even know where to begin. Perhaps I eventually ask my Heat/A.C. guys to do the work, we'll see.

Here is the link I was mentioning. After carefully re-reading it I noticed it says DO not cut into a existing supply line as you mentioned.

http://www.handymanhowto.com/2010/07...i-boot-part-3/
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Old 12-19-2011, 01:06 PM   #12
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how about just installing a couple of those electric heaters in the crawl space that look like radiators?
that way youre not opening your ductwork up to all those little critters that like to call crawl spaces home
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Old 12-19-2011, 01:10 PM   #13
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how about just installing a couple of those electric heaters in the crawl space that look like radiators?
that way youre not opening your ductwork up to all those little critters that like to call crawl spaces home
I hear you Plummen, that's an option I suppose but I fear having those fire prone items below my house running not monitored. Not to mention the cost factor for them to run. At least with the duct work conditioning the air down there I am gaining it back as the heat will rise warming my floors in the living space above.

As for critters thankfully I've never had a problem and now with me sealing it off completely I should hopefully really never have a problem, but it's always a risk I guess.
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Old 12-19-2011, 01:42 PM   #14
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thats why i recomended the oil filled ones that look like a radiator,no exposed wiring or elements to cause a fire.
if you keep the thermostat on them turned down to a lower temp they shouldnt cost you that much to run,you could always wire a gfi plug down there on its own circuit to monitor it if youre worried about it
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Old 12-29-2011, 02:45 PM   #15
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Adding an extra vent


Still trying to research this issue but really can't get definitive information. I am hung up on why I need to add a return vent when adding an addition register or two when my home is already equipped with two return vents. Size of them I am not 100% sure but can check.

Any info or advice would be much much appreciated.

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