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Will closing the registers on my 1st floor ducts


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There might be some ever so slight change, but the concept of "rebalancing" by opening and closing ducts is largely fantasy propagated by heating contractors. Air flow is about properly sized ducts and well placed registers and returns.

Try it anyway; sometimes it improves things.

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Many systems have balancing dampers in the ductwork. It may be worth a service call to have a contractor balance the system to make sure that the dampers are properly set (first check if there are accessible dampers).

Adding "High-Low" returns is also something to consider. Pull the warm air from the ceiling during the summer and the cool air from the floor during the winter.

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How many systems and thermostats do you have? I have 2 systems and 2 thermostats, one for each story. The chimney effect has more effect than closing/opening registers between floors in my home.

If you only have 1 system and 1 thermostat, different matter.

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Balancing dampers can have some minor effect if they are located down @ the plenum or at takeoffs from the main trunk. Minor.

Lemme explain using the plumbing analogy......(and yes, I know there are laboratory contradictions to the theory that I am about to propose, but for practical understanding, please don't apply them right now......)

If you put a know volume of water into one end of a pipe, the same amount comes out the other end. If you put a wye in that pipe, and divert a portion of the flow in another direction, you will still have the same volume of water if you combine the output from the two pipes.

If you put a known volume of air into one end of a duct, we know the same amount doesn't come out the other end....in fact, the loss can be calculated. Friction loss, static pressure, turbulence loss, etc....call it anything you want. You lose air flow.

Diverting portions of that air into another duct ("pipe") will complicate static pressure issues, usually increasing it. What that means is you may get even less flow because you're introducing turbulence into the system it wasn't designed to accommodate.....the air, instead of taking the other direction (like water would in that hypothetical pipe), will simply lose volume due to turbulence and static pressure. That's why duct balancers can't be introduced easily, and they only work (kind of) when they are integrated into the trunk line.

Factor in flex duct, and you got a real mess. The inside of flex duct is all ridges and uneven surfaces, so you get huge turbulence/friction loss.

Think about AC as extracting heat more than delivering in cold air; removing heat from the air is, in fact, what air conditioning is. If you ain't got returns at the 2nd fl., you're not extracting heat.

So yeah, you're screwed. Shoulda gone mini-split, or ductwork alterations. Diddling around with ducts like your guy gets you....ummm....diddly.

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Kurt- I agree with your big picture explaination. But...what if the balancing damper(s) to one or more of the second floor supply vent(s) has been inadvertently closed or someone has altered the ducts in a way that can significantly impact the second floor supply? I still say, start with the easy stuff and go from there. Maybe there is a simple solution.

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Kurt- I agree with your big picture explaination. But...what if the balancing damper(s) to one or more of the second floor supply vent(s) has been inadvertently closed or someone has altered the ducts in a way that can significantly impact the second floor supply? I still say, start with the easy stuff and go from there. Maybe there is a simple solution.

I disagree. It's fundamentally wrong but heck, if people understand it with that explanation...so be it. I'm just on record. You can put that record on a back shelf somewhere where it'll collect dust.

Marc

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You can't cut off air flow to the first floor in hopes of driving it to the second floor. If you cut off too much of the air flow you will start to ice the evaporator coil which is another problem in its self. You could try a VVT system (variable air volume/variable temperature - a type of a zone system) but it ain't cheap and may not solve your problem.

Google "inline duct booster fans". Their cheap and may help to some extent. Buy one and see if it works.

Good luck.

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If your gonna play with fans I propose you put a box fan upstairs and blow the hot air down toward your return, or even out a window. Measure the air temp at the upstairs registers for each scenario and compare notes. If it changes any, then the booster fans might be a viable solution.

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Sure it's "wrong", but I'm trying to explain it in terms people understand. Engineers never like simple explanations, and insist on trying to explain things in terms people have never heard of; it makes them feel smart, or something. It's like talking to someone that doesn't speak English, and when they don't understand, you talk louder. (FTR, I've had a couple air control technicians laugh, but also admit it explains the basic principles pretty well.)

My main argument against the "balancing theory" is in the thousands of elevator shaft 4 story town homes in Chicago with a single furnace on the first floor; they are an object lesson in why you can't just put in duct balancers and why booster fans are only vaguely successful. Static pressure wins every time.

As in all things house, sometimes you can do stuff wrong and it works anyway, so trying to balance air flow is worth the try.

Baseline, right now, the only thing that's gonna work at the necessary price point is a window AC unit.

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Kurt- I agree with your big picture explaination. But...what if the balancing damper(s) to one or more of the second floor supply vent(s) has been inadvertently closed or someone has altered the ducts in a way that can significantly impact the second floor supply? I still say, start with the easy stuff and go from there. Maybe there is a simple solution.

Engle sez that solution is inevitably wrong. Engle's a pretty smart guy.

The simple solutions are the one's Raymond's talking......put a cheap box fan blowing air down the stair, or extracting it out a window. Then stick in a cheapo window unit.

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The reason that not enough air comes out of the second floor registers is that the ducts have too much resistance to air flow. Closing the first floor registers won't decrease that resistance.

(How's that for a simple explanation from an engineer?)

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That's fine. It's helpful to explain to people why there's resistance, though. It's helpful, because.....

People naturally think if you shut off supply in one direction, it simply all goes in another direction. HVAC tech's routinely tell people it does, re: "rebalancing". It's also useful to explain air flow volumes as a component of design; coils and heat exchangers should be designed for a certain amount of air flow...taking out part of the flow gets you icing, inefficiencies, and it's hard on equipment.

It's hard to explain why the tech is wrong without backing it up with a discussion of friction loss/static pressure, length of run, etc. It helps folks conceptualize the process by tying it to something they do understand, i.e., plumbing.

Who here has explained amperage and voltage in plumbing terms? It works pretty well.

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Just to amplify what was stated previously, I would also point out that closing many of the registers likely will put a lot of back pressure on the system as you try to force more air through the upper floor ducting than it was designed for. That will result in a very noisy, whistling system. And unless your ductwork is beautifully sealed, it will also increase the amount of air that leaks out of every joint it can find. If any of your ductwork runs through an unconditioned space such as the attic or basement, then you are negatively pressurizing the home and unconditioned air will be drawn in from outside to replace it.

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This is the guy with 900 SF on two floors in a fairly mild climate. Two window units and two Eden Pure heaters and he's comfy all year long for less than $600. Hell, I'd be real surprised if it cost him more than that a season to run it all.

I bet the tech that butchered his ductwork cost him more than that. Sorry, but you got took.

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