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Old 04-05-2011, 11:34 PM   #1
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How to tap into existing ducts for basement?


I did a search and the first page didn't seem to have anything relevant.

I want to condition the space in my basement. Can I just tap into the central air ducts already there?

Any and ALL details would be appreciated. Thanks in advance.

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Old 04-06-2011, 04:49 AM   #2
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How to tap into existing ducts for basement?


Duct work placement

rearranging ducts

Use the search feature, and it will search all threads.

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Old 04-06-2011, 07:49 AM   #3
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How to tap into existing ducts for basement?


Every time I use the search feature (including this time) it brings up LOTS of irrelevant topics, and I've wasted lots of time trying to find answers. It just seems easier to ask my questions, and someone like you posts (most likely) exactly what I'm looking for. Thanks and I'll take a look at what you posted.
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Old 04-06-2011, 08:02 AM   #4
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How to tap into existing ducts for basement?


OK. I read both posts, and it's not enough info for me (the first timer). Can I tap right off the big ducts already there? So the vent(s) will be right there in the soffit I build around them? If so, how? Do I have to tap into the return? Or will just a supply be ok? What size vents do I use? Other materials, and hardware that might be needed?
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Old 04-06-2011, 10:49 AM   #5
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How to tap into existing ducts for basement?


What type of existing ductwork do you have (dimensional size, metal ducting or flex, etc.) How many registers are you thinking of adding? (individual rooms or an open rec room etc.)
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Old 04-06-2011, 10:54 AM   #6
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How to tap into existing ducts for basement?


You would want the supply airs to be near the outside walls so if your duct is in the middle of the basement you would tap off it with round pipe and extend out.
You would also need to add return airs.
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Old 04-06-2011, 11:09 AM   #7
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How to tap into existing ducts for basement?


Not an HVAC contractor, but a few thoughts:

The easiest and most common place to see new registers in a basement is the ceiling where they are tapped into the first floor duct work. Unfortunately, you also get the least benefit from heat supplied in the ceiling.

The HVAC system may not be adequate to handle the added load. Adding registers may meet your inspection/sale/valuation needs, but it may not work all that well, and it may decrease the benefits you feel upstairs.

Very broadly, by what % are you increasing the conditioned space? Are you adding 33% more space, 50%, 10%? It might be fair to assume that a 10% increase is within the margin for most properly sized HVAC units but 50% will not be.

Another problem is that basements are often poorly insulated. Even if the walls are retro-fitted with proper insulation, the uninsulated slab works as a massive heat sink, which can increase the impact of basement square feet on any HVAC sizing calcs.

All that said, many (most?) clients say the heck with it, we want the space, we need registers (and sometimes returns) for permits, we don't want to buy a new HVAC unit, so do the work and get out of our home. I understand that, and say ok.

Don't rule out a few electric baseboard units. They are not exactly sexy, but they may meet the need, especially if the basement is going to see a little less use than the rest of the house.

Have fun with that duct work!

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Old 04-06-2011, 04:26 PM   #8
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How to tap into existing ducts for basement?


Describe how your basement will be finished, and how it will be used, and how often.

Many times, electric baseboard will work better. using the same trunk line as the upstairs leads to a problem. The thermostat doesn't know that the basement is cold when its 65 degrees outside. Also, the coldest air from the first floor falls to the basement, and the warmest air in the basement rises to the first floor..
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Old 04-06-2011, 08:26 PM   #9
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How to tap into existing ducts for basement?


It will be a full basement (open, about 700 sq. ft.). Insulated, framed, and drywalled. I always hear people say it doesn't take much to warm the basement, so i figured it wouldn't take a huge toll on the system, and I could just add some vents that can be opened and closed. It will get used on a regular basis. Kids toy area, and an office area. I'll be closing off a portion to hide the HVAC system, water heater, and sump.

Here's a pic of what's there.
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Old 04-06-2011, 08:28 PM   #10
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How to tap into existing ducts for basement?


I was thinking I might be able to tap in at the opposite end of where the pump(?) is.
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Old 04-07-2011, 03:55 AM   #11
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How to tap into existing ducts for basement?


It doesn't take much to heat a basement. but the furnace does need to be running to heat it.

When its 50 and above outside. During the day the radiant heat from the sun will decrease the run times and how often the furnace runs, which will tend to cause the basement to become cold. Since the first floor won't be calling for heat. Its during these times that the basement will become cold.

Often, a basement needs to be its own zone to have it at human comfort conditions year round.
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Old 04-07-2011, 09:38 PM   #12
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How to tap into existing ducts for basement?


One of my other concerns was being able to keep the basement drier using the central air.
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Old 04-08-2011, 04:03 AM   #13
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How to tap into existing ducts for basement?


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Originally Posted by nateshirk View Post
One of my other concerns was being able to keep the basement drier using the central air.
Won't keep the basement drier per say. The RH will probably go up. You'll need a dehumidifier to keep the basement drier.
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Old 04-08-2011, 09:44 PM   #14
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How to tap into existing ducts for basement?


Thanks for all info.
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Old 04-10-2011, 07:04 PM   #15
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How to tap into existing ducts for basement?


So, I'll have a dehumidifier, or 2.

I still can't find ANY "how-to's". What to cut with? What needs mounted? How big of a hole to cut? I just want to know "how-to" do this. Search isn't bringing up ANYTHING on "how-to" tap into existing ductwork.

Is it just a dumb idea? I guess I can do baseboard heat, but what about cooling in the summer? And I have gas heat, so wouldn't it be more econimical to use that?

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