Air Conditioning - Recommended way to terminate two branch lines?

We recently moved into an office. This office used to be part of a larger office space, but the space was subdivided and remodeled previously. Looking at our A/C system above the drop ceiling, I discovered that there are two branch lines (they look like 8" dia ducts) running out of our space and into the office across the hallway.

I don't want to be a bad neighbor, but we are a start-up and can't afford to pay for the cooling of another company's office spaces. Furthermore, the occupants of that office are hardly ever in anyway. Further-furthermore, our office was vacant and unoccupied for over a year before we took possession, so obviously the neighboring office made it through the last summer just fine without the assist of our A/C.

So, that brings me to the technical question: what is the recommended way to terminate these two branch lines? Do I cut and cap? Or does that cause back-flow or other pressure problems? I don't recall even seeing duct caps at the hardware store for this purpose.

Suggestions? Thanks!

stop! call an a/c company before you get to pay for a compressor. Unloading your evap. can damage the compressor. Don't mess with stuff you don't know about or your start- up won't start.

Not sure what he is thinking about above, but I am assuming you are talking about the air duct (tubes) to the vents carring the air.

You can get the venting pipe and install an elbow so that it will blow the air down in your office and just put another vent in the ceiling. Leave their piping there or duct tape it off.

8" diameter ducts don't flow enough to the point that will upset the evap. and if you cut and vent them to your place by using elbows you won't be UNLOADING the evap.

One is probably a return and the other is a putting the air out so try to keep the out and in apart quite a bit when you put the elbow and vents in.

Looks like your free loading neighbors, get the shaft. there may even be butterfly's in the pipes you can turn to close off that path.

like last post Just get some 8" flex at HD and a piece of 8" pipe. Slid the pipe in the 8" flex just like a coupling and take the end over to where you want it in your room. do it to both runs.

ED;)

Thank you for your quick and informed replies.

I'm sorry, but I was not in the office when I first posted, so I was working off a memory of what I saw when I was running network cabling a couple of weeks ago. In any case, I am in the office now and just checked out the situation more thoroughly.

Yes, I was referring to two air ducts (and they are in fact 6" dia, not 8"). When I had first saw these two ducts passing through the wall to our neighbor's office space, I had assumed that they were conditioned air delivery ducts (or one delivery and one return). I was wrong. After tracing the lines, I just discovered that they are *both* return lines (one to each of our two ceiling mounted heat pump units). So each unit has two return ducts: a primary 14" duct (from our space) and a secondary 6" duct (from our neighbor's space). This baffles me!

(Btw, now I don't feel so bad about the neighbors, since they aren't receiving any benefit from us as far as I can tell.)

Anyway, it would be easy for me to cut the lines, cap (tape) off the lines that are from the neighboring office, and create two new return inlets in our ceiling for each of the two 6" ducts. Is that the best course of action?

Thanks again!

Get 6" flex pipe and run it to your side like said.HD has the 6" round register put them in your ceiling. Let the other ones where they are You dont have to cap anything.

ED;)

I guess there's one other question to ask: considering that these are two return ducts (with no supply lines going to that other office), is it even necessary to do anything? I guess we could be sucking in some of their office air and that their air may be at a different temperature than ours, but I'm wondering if it's enough to really make a difference.

I apologize for not having the facts straight when I first posted.

You decreasing the amount of time it takes to exchange all the air in your office and you aren't moving the air as much as you could.

Thanks Ed, I was writing my last question while you were replying so I didn't see your post until now.

I'll do as you suggest. Sounds like the best plan.

(I'm still a bit puzzled as to why these two 6" return ducts even exist, given their routing from the office space across the hall and the lack of supply ducts to that office space. But i guess there are some things people shouldn't question.)

Thanks Hotrodder89 for your assistance!

I'm sorry, I was thinking they were going to totally block off the airflow in that branch. I'll stay out of other peoples business.

sorry

every one misreads threads because you have to decipher there non jargon descriptions they can be confusing sometimes. There was an A/C one below that I was reading that said exterior fan not working. I was like what in gods name are they talking about. Then some one wrote replied about the condensor fan for the A/C, which then it dawned on me I can see why they called it that.

When I read your post I knew how you interpreted it. Sometimes they put to much useless info or wording and make it near impossible to follow