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Airflow in ductwork/fan questions

841 Views 13 Replies 2 Participants Last post by  wolfgang953
Im curious to know/ figure out if duct fans are an option and how to calculate out how much or many would be needed in this type of application. - For the moment its a theoretical/planning idea. And im aware its more of a jerryrigged idea then a proper solution. I got a few estimates on a mini split ac system, but even for a single room the estimates were around $4k. So im mulling over the more outlandish ideas that might be a tad cheaper.

Some misc info.

A little while back i was considering adding a second portable ac unit to a room in the basement. There is currently one portable unit down there which is able to keep up with the temp needs pretty well. But when a dehumidifier is turned on, then the AC cant keep up and the temp slowly rises. I have temp sensitive animals down there. So the room must be kept cool at all times. - Its possible that better air circulation might help this issue, im not sure. But the ceiling is to low for ceiling fans. Even roof huggers. Between the height of the cages, and the main house ductwork and house support beams.. theres to much in the way + low ceiling. So ceiling fans dont seem to be an option.

I dont want to set up normal fans because the animals should not have direct drafts on them. So a normal fan might be to powerful even on a low setting. That being said, i already have one portable AC unit, and one dehumidifier. Id like a second dehumidifier to help keep up better. So if i added a second portable unit, then id have four various units and could arrange them to make a little bit of a circular air flow across the room. (remember when i said a more jerryrigged system?... yea.. )

But all of that would be irrelevant if i couldnt set up a second portable AC unit. Trouble is, there no where near by to vent the air in and out. So it would be a long ass duct run. And the port ac units arnt really designed with that level of power to draw the air in and out over that kind of distance. So i was considering those duct fans with a temp control for turning on and off to help move the air.

Which begs the question of how do i determine how much help would be needed? How many fans, or how strong a fan to make such a system work? - Unfortunately, the unit i have now, which i was going to use as a mathematical base, doesnt list the air flow force of its intake and extakes vents that i can see. So i cant even give a solid number for what it would need or what it currently has.

This is the rooms current setup

I havnt made a final decision cause i dont have all the info, obviously, but i was considering something like this.

The only good idea iv found so far is the mini split system. But at an estimated $4,000.. id like something so not damn expensive. So im considering not so pretty, jerryrigged systems. I would just have to make sure it would worked. The ductwork for the second port ac system in this example would be ~14ft outside the room, and 18 ft inside the room. A long duct for sure, hence the idea of the fans to help the air flow.

So if anyone can tell me how to go about finding out what level of airflow help i would need from the fans to make this work, please let me know!
Or any better ideas i dont know of, tell me those too! - I just need to come up with something that will work and not be a fortune; like a $4k mini split.
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Quit avoiding the obvious. Installing a mini split is much easier, more effective and possibly cheaper than what you are proposing. This is a DIY site, plenty of support here. Size of unit in link is not necessarily what you need.

I dont have the most remote clue as to how to install these things, much less the tools to do so. Before it was suggested a couple weeks ago on here, i had never even heard of these things before. And i get a good feeling that me trying would be well over my head. - Also, im on permanent disability. Thats not exactly the best money maker out there. So hiring anyone i got an estimate from is not really an option. That would be 4 months straight income for me; assuming i didnt pay a penny for any other bill or food or anything..

So yea, i know its a crappy situation.. i just dont have many options at the moment.

Edit: even in the q&a section of the unit you posted the link to, ppl were saying that it was a hard install. And not only that, but doing it yourself voids the warranty. That may vary with the unit offered, but i see a situation of me not being able to do the install and having wasted a ton of money.
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Tough spot to be in. Do you have family/friends that are handy that could help out? Since you have existing duct work you could check into financing central air for the whole house, many dealers offer this. Might be tax deductible if it's a medical necessity.

Nope. Had to move out of the state i was born and raised in after my father died. His insurance is the only reason i have a house to live in. Certainly couldnt afford it on disability.

A whole house central air system seems like a massive over kill to cool one room. There is one here now, but its 30 years old. And the thermostat is on the first floor. I need to be very specific with the animal room in the basement. It would probably cost a lot to run a whole house system for one room too. - One of the companies i had out to give an estimate for the mini split took a look at my furnace and central ac system since he walked by it. He noted the company name on the paper work on the side of the unit. Said they were getting out of the game just as he was getting into it back in the early 90's. (System was installing in 91 i think.) Not only would the furnace and central ac need updated, but he mentioned even the type of duct work used for it isnt even used anymore. And said anyone replacing the units one day would likely recommend replacing the houses duct work along with it.

And i highly doubt i could get away with claiming that as a medical necessity for a physical injury. Besides.. the animals might need the cold to survive, but i usually hate it. I lean toward heat. My bedroom is usually hovering around 90 the last two weeks. Which i can tolerate, but the humidity has made it a pain.
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I'll probably get flamed and shamed for this but desperate times need desperate solutions. Connect the intake condenser air of the portable a/c's into the supply duct and tie the exhaust air into the return duct of the existing duct system. Close/seal any supplies in basement.You said you like it hot upstairs, right? Won't work very well if your heat is on. Don't forget to unseal the basement supplies before heating season. Might work well enough to forgo a 2nd dehumidifier.

im not sure i entirely follow that (sry).

The portable unit currently has both its intake and extake that go outside.

As for the main ductwork for the house, so far i havnt really used it at all aside form when i made sure it turned on before coming here. But i dont use the central ac. And in the winter i havnt used the heat because of the oil costs. Iv jsut had the bedroom with a good space heater. (i rent out two of my rooms to help cover the bills. So i try to let each room have its own temp control.)

Or are you talking about a second ac unit connected into the main ductwork?
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I might also add/admit that there is a certain level of annoyance to this for me. The portable ac im using has been able to keep up with the temp from the weather. So far its only when the dehumidifier is running that the temp in the room starts to climb.
those house ducts go into the furnace right on the other side of the wall (bottom of pic). Would they be able to pull in the air effectively?
I should have thought to ask about this earlier. One reason i like talking to ppl about things on sites like this; sometimes my mind gets hung up on a specific detail or two and will miss some obvious things.

Think this would this work? Its a little bit of a long duct run, but much shorter then any of the others i asked about. And it would only be a few feet longer then what it already is.

Id rather have had the ac's on opposite ends. But that seems highly problematic at best. - Since i already have the AC in this pic (on the right side) there, it would just be extending the vent a few feet out more. - Im not sure if it would bring in enough air to the condenser for both tho.

(What it currently is)
The actual ac unit i have there is right under the main house duct work. So i measured it, it would mean extending the port ac duct work 3 maybe 4 feet more.
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slightly different question.

The air coming into the ac units condenser through through the intake vent; how much of that enters the room? Or more generally, how much outside air is a port ac putting into the room?

I wouldnt have thought much/any. Considering its a basement room. Concrete floor, insulated walls. Granted, non insulated ceiling but im trying to keep it cold, not hot.

But last night when i walked into the room, i noticed the same burning air smell as the outside had. (fire going some where). I also noticed the last couple days that the humidity level in the room was staying the exact same % even with the humidifier running the entire time. - Which would suggest that maybe some outside air was coming in? Or something was bringing in more humidity at a rate equal to the dehumidifiers ability to take it out.

If i could find a way to deal with humidity more efficiently, then that would cut down on the hot air the unit blows into the room and would make the ac's job easier.
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~~~ Completely different question ~~~

Still regarding the duct work for portable ac's tho. - For the ducts themselves, is there any functional difference between using a solid metal duct pipe vs a flexible insulated pipe? Other then the obvious insulation aspect.

I was looking at duct pipes and was surprised to see that per foot, the insulated flexible was cheaper then the solid metal duct pipes. I would have thought it the opposite. Which now makes me wonder if theres any functional difference, in air flow or anything else i might not know about.
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