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Extending HVAC Ductwork
When people are planning to change layout of their ductwork, finish a basement off, kitchen remodeling or other renovations they are usually buying my books and/or paid pages, because there is no other place to go. But, not all of them! Some of them are looking for help on the Forum websites. Below you can see one more example:
Question
Extending HVAC ductwork. Hard to DIY?
Hi. New to this forum here. I'm a big fan of DIYing. I don't know everything, but like to learn stuff and do it on my own. Previously, I have replaced windows, renovated my kitchen, put in new recessed lights, done tile work, etc, all by researching beforehand as well as learning as I went along. But I've never done any HVAC work before. So here goes.
My main furnace/blower is up in the attic and has a hard time warming up the 1st floor adequately during the winters. Well my basement has a separate furnace/AC for the basement alone. I recently replaced this furnace with a new high efficiency one since the old one was dying. I'd like to cut out some 4"x10" floor registers on the 1st floor and extend the basement ductwork to share some of the heating between basement and 1st floor. That way, 1st floor will be heated mainly by main furnace up in attic, but also by basement furnace when it kicks on.
First of all, this is the layout of my basement. As you can see, current duct runs along right wall, almost the length of the basement.
 I would like to take part of the duct down, and cut two holes on top to create feeds for the new 1st floor registers.
(1) Register will sit right on top of where duct lies. So that new duct will just go straight up between the ceiling joists and thru the ceiling/floor.
(2) Register will sit on the other side. So for this one, I'd like to up from the current duct into the ceiling cavity, make a 90° turn and go across between the ceiling joists so that I can have a flat ceiling when I finish off the basement.
 
This is my plan anyways. But since I've never done this before, I'd like to know if there's something I'm not thinking of, or not aware of. How big of a duct will I need for the cross run? Will a 7" round suffice? The cross run will be about 13-14'. What other materials will I need? What should I know when performing this. Any info helps. Thanks
Well as you can see OP has a lot of questions, which could be easily answered on my website!
Answer
What about return air?
If you run supplies from that furnace to your first floor. You need to also run a return. Or else you won't get much air to the first floor. And you will put your basement into a negative pressure. And could draw CO from your water heater and furnace. And harm you and your family.
Keep in mind. That the cold air from the first floor will fall through the new duct work and cool your basement off quicker after you do this.
This guy offered his very usual answer, which is useful only in general terms, but did OP get what he expected? You decide!
Question
Will adding two more openings really over work it though? It's a 45k BHUh Ruud 2 stage furnace that has 890 CFM at low setting, and 1140 CFM at high. Right now the basement duct has 3 registers, and the basement is 500 sq ft. after finished off, the heated area will be ~400 sq ft.
 The return air will remain where it is. I will create a partition wall where the return box begins with a big opening for the return register, and the furnace will be getting it's return air from the finished part of the basement.
Thermostat and return for basement furnace will remain in basement. Thermostat for main furnace is on 1st floor (I wont be putting the new registers anywhere near the main thermostat). The basement furnace will kick on when it wants to, and throw some added air into the first floor as a bonus.
Before we go any further, look at this installation! The hacks were doing that! There are so many mistakes I do not even know where to start! This installation should be posted on my "Wall of Shame" page!
Answer
Since its hard to get a furnace any smaller then 40,000 BTUs. I understand why you have such an oversized furnace for your basement.
If you don't have a large undercut on your basement door. You'll put the basement into a negative pressure. And it will draw air from everywhere it can. Including from the water heater's chimney if you have a gas fired water heater (can't tell from the pic).
Cold air will fall from the first floor through the supplies, and cause the furnace to cycle more often. And may cause some over heating problems in the areas that you install the supplies in when it does run.
Again, there is very useful information, but what about some help for OP?
By the way, this installation is so bad that I would recommend him to purchase my Ductwork Installation Guide's Basement part.
Answer
Someone please correct me if I am wrong, but that looks to me like a horizontal evaporator coil laying on its side.
Tinmanrob probably meant "vertical".
Answer
Might be a half case coil.
So far I do not see any additional posts in this thread. May be I'm wrong, but its looks like that Aharami gave up, and is looking for help some place else, maybe he is even looking for my website? Who knows...?
Okay, so I have some bad news - this thread is officially dead! OP has never come back to that Forum website, probably because he realized that it's useless.
However, he was very committed in his pursuit to find some necessary information online, so that is why he opened a couple more threads on some other DIY websites! On one professional website no one even bothered to respond, but on another he eventually got what he wanted, but... But, I would not suggest him to follow these recommendations, it's why I am not publishing them here on this page.
That particular Forum website is not a professional one. There is just a crowd of DIY-ers helping each other by offering free advice on everything they know or heard from somebody else. Some of them have some rudimentary knowledge, and they are itching to spread it out.
However, OP is thinking that he got a good advice and I won't tell him otherwise... Let's keep him happy!
So, why did all these pros simply ignore that thread? Here is a very simple explanation:
Would you give me a step-by-step instruction on how to do your job free of charge? I do not think so!
Did I say that another DIY Forum website didn't even bother to respond, didn't I? I was wrong! They just woke up:
Answer
Well, I can't say I recommend what you're doing, but just a little advice & some HVAC factoids anyway...
Your basement furnace won't push (much) air into the upstairs unless you allow it to suck some out (of the upstairs). Air is like spaghetti, you can pull it all you want, but pushing doesn't work very well.
Air returns are NEVER in "wet" rooms - don't pull air from kitchens or bathrooms.
Air returns can be "panned" across joist-work, and hollowed out of wall space, but WIRING IS NOT ALLOWED in air return space.
6" is the "standard" duct size for one register.
At a minimum, remove the paper from the insulation under your floor joists in any area of the basement that is heated- a minor temp. differential between floors will cause condensation & mold if there is a vapor barrier (paper) present.
If this finished area is only going to be used infrequently, and left "cold" most of the time - your plan will likely result in a very un-comfortable upstairs whenever you do fire it up. It could take a long time to warm up the basement, and in the mean time, you're dumping BTU's upstairs, which likely doesn't need them.
At a minimum, install "dampers" in the ductwork leading upstairs so you can minimize airflow if you need to. They won't be expensive, they're just a round/flat plate with a small lever you can close to block off an un-needed duct.
OK, is this a good thread? Yes it's a good one. Could you consider this post helpful? I do not think so! Why?
Where is a list of tools and materials? Where are the step-by-step instructions? I do not see them here at all.
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