Understanding Air Flow | Ask This Old House

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In this video, This Old House plumbing and heating expert Richard Trethewey and home technology expert Ross Trethewey explain everything you need to know about balancing airflow within a home.
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Kevin O’Connor meets plumbing and heating expert Richard Trethewey and his son, home technology expert Ross Trethewey, to talk about airflow. Richard explains that most folks with forced hot air or central air conditioning dislike their air distribution, and the Tretheweys explain the options.
Most Folks Aren’t Happy With Their Heating and Cooling System
Most American homes have hot air heating or ducted cooling systems. And, seven out of ten of the folks in those homes are unhappy with how they operate. Much of the reasoning behind their unhappiness is air distribution and how some rooms receive too much air while others receive too little.
Air Travels the Path of Least Resistance
Physics is constantly fighting against ideal airflow. As the main duct routes through the home, smaller ducts branch off. If these smaller ducts are left wide open, the majority of the air will pour out through the ducts closest to the furnace or air conditioner, while the ducts at the end of the line will receive very little airflow. This is because air travels through the path of least resistance.
Dampers are the Answer
It’s possible to control airflow by installing differently-sized ducts or adjusting louvers on air registers, but most homes can benefit from dampers. Dampers can control the amount of air that flows through the branch, helping distribute air more effectively.
Different Types of Dampers
Like most things, there are lots of different types of dampers. Some do a better job than others, so it’s a good idea to become familiar with each type.
Metal butterfly-style dampers [thd.co/3tFJAS8] install inside a standard duct. They’re relatively easy to adjust, but they rely on a thumbscrew to keep them in place. Vibrations and airflow can loosen these thumbscrews and affect the flow.
Iris-style dampers [bit.ly/3O37wXK] have adjustable and lockable lenses that allow for properly targeted airflow. They install between pieces of duct, and their lenses open similarly to a camera shutter, providing quiet and reliable airflow.
Automatic volume dampers [bit.ly/3zIZYFg] self-regulate airflow. These devices have settable airflow volumes that the user can choose, and the spring inside the damper automatically adjusts to ensure the proper amount of air is passing through the ductwork.
Cable-operated dampers [thd.co/3xWFurn] have long, stainless steel cables that travel from the damper’s locations to the register. Inside the register sits the damper adjustment, and tweaking the adjustment opens and closes the damper. They’re an excellent choice for ductwork hidden in ceilings or walls.
Where to find it?
Richard and Ross use dampers and drain valves to demonstrate how balancing airflow throughout a home is achieved.
Cable operated dampers [thd.co/3xWFurn] can be found at Home Depot [www.homedepot.com/].
CAR3 Constant Airflow Regulator [bit.ly/3zIZYFg] is manufactured by Aldes [www.aldes-na.com/].
Duct Iris Damper [bit.ly/3O37wXK] is manufactured by CFM Inc. [select.cfmfans.com/?refer=con...]
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From the makers of This Old House, America’s first and most trusted home improvement show, Ask This Old House answers the steady stream of home improvement questions asked by viewers across the United States. Covering topics from landscaping to electrical to HVAC and plumbing to painting and more. Ask This Old House features the experts from This Old House, including general contractor Tom Silva, plumbing and heating expert Richard Trethewey, landscape contractor Jenn Nawada, master carpenter Norm Abram, and host Kevin O’Connor. ASK This Old House helps you protect and preserve your greatest investment-your home.
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Understanding Air Flow | Ask This Old House
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24 июн 2022

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Комментарии : 124

@ctfplumbing4910 Год назад

Richard, your plumbing work is the best! I’m your biggest fan!

@glorygloryhallelujah 2 года назад

Wow. Best demo of airflow ever

@ParniyanKarimi 8 месяцев назад

thanks for this useful content!

@briandurant2145 2 года назад

Great information!

@tonystrollo193 2 года назад

Great new solutions for the future, the Iris is the best, then the cable adjust, is also a good product in the event you need to change air flow.

@DemoniqueLewis 2 года назад

My parents and I were talking about air flow today. We were trying to find the dampener for the Maine floor of a colonial. Looks like the primary duct is in the ceiling of the basement without any dampeners and ceiling registers. So the water example really helped explain why it is so hot on the Maine floor.

@mrtv777 2 года назад

This was a great example. We get it now.

@pointedspider 2 года назад

I love this show

@gl15col 2 года назад

I would suggest to never install drywall as a finished basement ceiling. If anything goes wrong with the ducts or there's a leak on the floor above, you have a huge hassle to take care of it. Just put in some nice ceiling tile that can be removed right where the problem is.

@Andywmm9 2 года назад

I like drywall better for a more finished look, but I put access panels for anything that would ever need service in the future.

@cbermudez281 2 года назад

If air leaks all it makes is a sound. It’s not that serious if there’s a leak.

@bigsparky65 2 года назад

Very interesting, wish i had that type in my house. I have window AC, old steam radiators

@phototristan 9 месяцев назад

I certainly have experienced this. When I was in college I rented a room in a family's house and my room was the farthest away from the air conditioner unit. It would be 85 degrees in my room and nice and cool in the other rooms. They still made me split the electricity bills equally though so I ended up moving out.

@Aaron-kj8dv 5 месяцев назад

The house I grew up in was like this. Me and my brother were melting upstairs and my parents just thought we were whining until I took an oven thermometer and took a photo of it to prove it.

@Alex.AL_26 2 года назад

Surprised nothing was mentioned about automated zone systems. I have a thermostat in each room that is connected to damper that opens or closes electronically based on the temperature in each room.

@shanew7361 2 года назад

I agree and this has been around for years.

@MariuszChr 2 года назад

Guessing air handler is providing static air pressure? That's the problem. Sure handler needs to adjust - have variable power/speed to make it work properly. Closing off completely one register, which was meant to provide air flow will unbalance the system and can lead to problems. I believe they didn't mention it so no witty diyer start putting this into their one speed system...

@RandomVids519 2 года назад

You are too rich for this site

@gl15col 2 года назад

@@MariuszChr Yes, that's why all the doors in my newer house have a big gap under them, so air can move even when door is closed. Newer furnaces should never have a floor register completely closed off as it puts a bunch of stress on blower.

@Egleu1 2 года назад

@@gl15col your house probably leaks sounds like crazy. You don't need a big gap under the doors if each room has a supply and return.

@facklere 2 года назад

This was really helpful for me. The upstairs and downstairs temps of my apartment were always drastically different - I measured the temp upstairs at 8 F warmer than downstairs last week. I had just resigned myself to the fact that we had a crappy AC unit because it's a rental. By closing off the vents downstairs somewhat (where the air handler is) I've gotten the upstairs and downstairs temps to match and it's so much more comfortable. Thanks!

@Lughnerson Год назад

Are the stairwell open? The stack effect means hot air rises, so with open stairwells the downstairs hot air rises to the upper floor. I have seen, but not used, ceiling curtain tracks which hold long curtains that reach from ceiling to floor. I think those curtains would lessen the stack effect.

@dianedoncheski2302 Год назад

That's really unusual you have an air handler downstairs!

@xslabcabxhearsex 2 года назад

Been doing heating and air conditioning/ sheet metal mechanic for 33 years.the biggest problem is poorly designed duct systems.not sized right from the beginning.few companies are putting in proper sheet metal duct work that is sized correctly.instead it’s just a bunch of flex and box crap that doesn’t work well.the art of sheet metal is hard to find these days.

@mrtv777 2 года назад

It’s beginning to be a lost art basically. Nowadays it’s all about slapping it in the home in record time. All about quantity not quality. Sad

@rupe53 2 года назад

@@mrtv777 ... new condo construction is often 6 or 7 inch to every room, and all off the shelf from a big box store. In most cases people don't even notice a balance problem till after a few months when they start closing doors between rooms and finally figure it out when seasons change. The most common problem I hear is about a bathroom being drafty because it's also got a 6 or 7 inch feed.

@markcooper4380 5 месяцев назад

Hello, I love the iris balance damper and will consider using them on my Smart's Warm Air domestic heating in future. Where can I get them in England please. Made in Canada 1965, still working fine, but the balance could be improved. Thanks for you help.. Marco

@yahanwiwi 2 года назад

Companies also make register boosters. AC Infinity has decently priced units starting well under $100.

@heroknaderi 2 года назад

Nice

@tonyegg2.073 2 года назад

I'm a Scottish plumber, I love watching Richard our systems are totally different from yours but He is always clued up and informative

@linadixon3409 Год назад

My house was built in 2009 and I moved in a few years ago and the 2nd floor has 4 cold air return vents but just found out they are not hooked up . Is it possible to hooked them up and would it make a difference in evening the house temperature. In the winter the house is 2 ½ deg cooler on the second floor than the main floor and summer 2 ½ degree warmer. One cold air return on main floor (working). None in basement. House is 1537 square feet.

@Jacarroll417 2 года назад

My bed room used to be very uncomfortable. We ended up using cardboard and blocking the register all together. It was so bad that even in the dead middle of Michigan winters Id have to crack a window because it was too warm. Me and my dad would fight over the thermostat, he would turn it up and I would turn it down.

@loganverdery2167 2 года назад

Yes

@ThreeRunHomer 2 года назад

That’s one of the reasons ductless split systems are becoming so popular, at least in smaller homes.

@habebs7345 Год назад

We bought a house with all the air return vent covers with the insulation and carpet can you tell how bad is this not allowing air flow and what are the damages please

@hansjansen5224 2 года назад

If the ductwork was laid out properly to start with airflow would balance. This would involve some prior calculations by the installer. There is even software available to help thru the process. But it takes time which most HVAC install companies don't want to spend.

@Lughnerson Год назад

Open stairwells allow the stack effect, which causes temperature differences from lower to upper floors. But I have not seen this addressed. The stack effect means warmer air rises, so with open stairwells the downstairs warm air rises to the upper floor, whether it is heating or cooling season. I have seen, but not used, ceiling curtain tracks which hold long curtains that reach from ceiling to floor. Using those curtains would lessen the stack effect, I believe. Or build enclosed stairwells. Multi-level homes would have less temperature divergence, more comfort, and energy savings.

@Immobiliermarrakech5933 2 года назад

Good 👍 💪😎

@loganverdery2167 2 года назад

It's always good to be back with The Times silver

@jimg8218 2 года назад

What about return air vent placement

@user-yu9lp8rg7g Месяц назад

I am in Atlanta Ga in a 1963, 1650 sqft house, and nobody is competent enough to help me. I am so frustrated. My house lacks the proper number of vents and the duct work needs restructured. So in the summer I can only cool to 82 degrees and I have to deal with it because no individual or company has been knowledgeable enough fix my problem. I need all the advice I can get!!!’ Thank you

@morrismonet3554 2 года назад

I had hot water baseboards put in when we put the house up over 35 years ago. Last year I finally replaced the original boiler. The whole house is a constant even temperature. Duct work sucks and is bad for your health.

@bobm5951 2 года назад

The pipes for the example are different. One has the outlets point down and the other is out the side. Of course it'll come right out the first one if it's pointing down. It would with the valve too.

@MrEazyE357 2 года назад

But you can also have registers and/or ductwork pointing in different ways so it's kinda the same thing

@loufresquez8031 2 года назад

What about old rectangle ducting

@Craigthepope 2 года назад

Not pictured: Flex ducts which are common in the South. Flex ducts also must be installed correctly no slack and no sharp turns,

@CuddleTrouble Год назад

All the smaller rooms in my house create back pressure because they have no where for the air to escape so they don't get warmed or cooled well at all.

@demagab 2 года назад

Mini split (all kinds) is the way to go.. every room gets the perfect airflow and the perfect temperature

@thecloneguyz 2 года назад

And cost you 10 times more than a heat pump over time

@bonita1228 2 года назад

Wish I knew more about this before I got screwed by Costco approved sub contractor. They installed my new air conditioning and ducts.

@gl15col 2 года назад

I didn't know anything about what size I needed, and they installed a air conditioner that is too big, so it runs for only a short time to get the temperature down, which is never long enough to deal with humidity. The temp says its fine, but it's never really comfortable. Won't take the word of a contractor again!

@JT-lq4yd 2 года назад

0:32 here it's discussed. the question that needs to be asked, if they do a load calculation? If HVAC contractor does not know or care to do one, try another contractor who does. Also, sometimes the one of the units that is currently installed may be the wrong size for your home.

@wampastompastomp 2 года назад

how big of a house do you need to have for this to become a problem?

@bmac3625 2 года назад

What about flex ducts that are run between floors on a 2 story house?

@mikeclarke3005 2 года назад

Installer should not be in that line of work if that was done

@markbyrd4549 Год назад

Does anyone else find that too often vent covers never seem to attach to the ceiling because the duct work was totally lacking appropriate fasteners? I would really like to hear how you all mitigate this particularly if you are unable to change the duct work.

@BitmappedWV Год назад

Can you use a wall anchor?

@TheBobbyMetcalf 2 года назад

distribution of air is dictated by static pressure more so than proximity to the blower fan

@MattFerguson26 2 года назад

Those two are directly related.

@TheBobbyMetcalf 2 года назад

@@MattFerguson26 no kidding it's all related, but his water through pipes example was too simplistic not to comment on

@rzh3443 2 года назад

One of things that they didn’t mention was the requirements for static and differential duct pressure ( essentially duct resistance to air flow) listed by the furnace manufacturer. I found out the hard way that if these requirements are not met ( closing off vents create back pressure) they put a lot of strain on your fan motor. The newer ECM DC motors seem to require much lower resistance , probably assuming modern ,well designed ductwork. The older AC motors were not as efficient but could blow air through anything! Ask your HVAC person to use a manometer to measure the pressures. If he or she looks puzzled, you have your answer.

@mrtv777 2 года назад

The good old days when things were built to last and no concerns for efficiency.

@rzh3443 2 года назад

@@mrtv777 Yep. The ECM motor labor replacement , although covered by a part warranty , negated any savings in energy cost for the time period! This stuff is nice when it works but when it doesn’t it costs a bundle to replace. The replacement stuff goes to a landfill and energy and resources are used to replace it. I learned my lesson.

@raindogs451 2 года назад

It doesn't strain the motor. the system essentially 'runs high blood pressure' and as a result, less flow. The greater problems are elsewhere and less obvious

@KLAWNINETY Год назад

Biggest problem with drop ceiling is it makes your ceiling lower. That's why you want drywall in your basement. *COMPROMISE* finish your basement ceiling but leave an access panel or something

@rupe53 2 года назад

Maybe I don't have to point this out, but it seems to me that some of these solutions are just the better mousetrap. If you have access to install a fancy damper, then you also have access to manually adjust the $3 damper. If you don't have access, then the damper should probably be in a better location, like near the trunk line. (where it will make less velocity noise)

@rayRay-pw6gz 2 года назад

They install the dampers where the trunk meets the offline run . In many cases they just adjust them during installation. Problem is that owners change them and sometimes cover the system to hide the ductwork. My furnace was installed under the bedrooms with the living room and kitchen at the far end . I ended up shutting off all three bedrooms . In the basement , I have a exhaust & intake which I closed both. When the furnace runs it takes the air from the basement ( which may contain radon) out thru the chimney. The foundation area is not sealed . The far end of the house gets all the heat and radiates to the bedrooms , which should be cooler. I went from a 120,000 BTU FURNACE to a 80,000 BTU . First furnace 1963 to 2015 replaced fan motor 2010 .

@starkyslp16 2 года назад

For the last example... why not just push the damper open or if needed cut ceiling and remove, then install a new accessible one earlier in the run? That way it can be serviced if needed and likely a cheaper damper type to retrofit

@gg80108 Год назад

Do the major builders with all their resources and cookie cutter homes actually figure this out. Or do they just subcontract it out with no quality control? Do they depend on the register faceplate dampers?

@victorsr6708 2 года назад

The iris dampers look cool but are very restrictive!!! On a typical residential system we only have .5” of static pressure to play with. The A coil = .1” the filter is .1 1+1= 2 right? So we only have .3” of SP for ducting and the typical very restrictive cheap supply registers most people install, oh did I mention duct air leakage??? The idea create the least amount of restriction as possible NOT to add restriction. Look up the Reynolds number Laminar flow VS turbulent. These iris dampers cause a lot of turbulence and uses up our our static pressure.

@ianmackenzie686 2 года назад

I miss radiated baseboard heating systems.

@loganverdery2167 2 года назад

Hey Kevin O'Connor

@loganverdery2167 2 года назад

I would love to learn how to use the hammer

@meme-yc4ks 2 года назад

Putting in one of those Iris dampers can also mess up your blower motor on your furnace. Normal AC mode calls for the blower motor to turn on High, where as on heating its usually set to low or med-low. Installing one of these does regulate the amount of air going to a particular room, but its not like the air 'flows' backward against its own airflow to other rooms where airflow was a concern. What it does do is creates resistance and almost a back pressure in the duct system and at the heart of that is where all the flow starts....your blower motors resistance. What they miss here is the system should be properly air balanced by an expert. At best these should be put in the very beginning of a run so as to create the least amount of back pressure to the resistance of the blower motor and least amount of turbulent air in the ductwork.

@raindogs451 2 года назад

That's unheard of in houses, but a very specific set of skill sets and tools for commercial buildings, and it's typical in commercial buildings. (but hardly universal) Unheard in homes though

@meme-yc4ks 2 года назад

@@raindogs451 Unheard of in homes? LOL what planet are you from? They do air balancing for forced air in homes all the time. I mean TOH even did a prior episode all about it.

@Try2-Imagine 11 месяцев назад

So there is no solution you can install at the registers? With all the bluetooth and wifi there has to be a high tech solution.

@loganverdery2167 2 года назад

This is Logan

@TheDuke013 2 года назад

Wouldn't decreasing the diameter of the large duct as it progresses increase the air flow to the furthest vent as well?

@joeychgo 2 года назад

Trouble is, the iris dampers are $100 each - count the vents in your home - awful expensive

@mmjohns2705 2 года назад

Just buy one, find the right size/flow and then get a 6” to x” to 6” couplings. And then return it 😂

@shanew7361 2 года назад

Who cares it will pay for itself in the long run and you'll be comfortable 😉

@abc123fhdi 2 года назад

Maybe there should be a way to get a wifi connected system that you can open and close with an app.

@joshuaseaton4526 2 года назад

What they got wrong is that air will pressurize and push back the air more evenly. The water demonstration is incorrect. A duct filled with air will build back pressure and change the dynamics of take-off locations. Balancing dampers are still needed, but not in the way they are showing. HVAC business owner here, 28 years.

@cj5782 2 года назад

That fitting probably costs more then a run of flec duct

@MattFerguson26 2 года назад

You get what you pay for. Flex duct adds significant pressure loss.

@sharpshooter012345 2 года назад

5:24 you ask the tooth fairy (the rock) for help.

@rynedude 2 года назад

So why not use the registers on the floor? This seems overly complicated

@gl15col 2 года назад

They explained that.

@rupe53 2 года назад

the short answer is closing the flow near the register causes velocity noise or whistling. Closing it down father away makes less noise.

@Vlican 2 года назад

if they're not disturbed, they work fine. don't let the kids touch them, or hit them with the vacuum

@rupe53 2 года назад

@@Vlican ... that's another good reason. What I forgot to mention the other day was furniture blocking the air... and the returns suck up all kinds of dust bunnies. In my experience, you need to change the filters twice as often just for that issue alone.

@LuckyFalang 6 месяцев назад

@@gl15col Gets hit by vacuum vs all those other expensive solutions.

@anthonyfigueroa7869 2 года назад

How a OBD ???😇😇😇

@MPDLR 4 месяца назад

Great learning here, thanks. OK FOLKS - PLEASE HELP. 2 years ago had 100% new Furnace/HVAC installed. And, other than my leaky crappy windows - yeah, the house warms and cools. *But* all of a sudden - my basement is really really cold. As in, I need a winter hat and 2 sweaters to watch TV down there. Fully finished basement. I actually feel a cold breeze sometimes - but for the life of me can't see where it comes from. It happens when NO heat or A/C is operating- my suspicion is the breeze happens right before heat kicks on. I've literally slept next to vents in basement. At best a tiny trickle of air - sometimes but there's no way that freezes a 1000 square foot basement. Exhaust fan in bathroom I out my hand on all the time - no cold air there. I've hung toilet paper everywhere - once in awhile I see the paper wiggle. And I'm totally still and no heat/AC is kicked on. But again dont know where the heck the air comes from. Any ideas??? Could it be leaky ducts - shooting cold air thru the ceiling tiles into basement? Appreciate any thoughts, thanks.

@inspyral02 2 года назад

The people need air.

@RandomVids519 2 года назад

Hvac is always more of a problem then hydro

@GoatZilla 2 года назад

putting the "old" in air flow eh

@Z-Ack 2 года назад

Is like a booty hole for the central air.. controlling its wind.. nice..

@victorsr6708 2 года назад

His main trunk idea is NOT how it’s actually designed by anyone with any experience. The design distribution work is the following…. We design to static pressure for residential we usually use .10” of SP the goal is to maintain .10” of static pressure all the way through the system so that air is delivered per design meaning correct CFM & velocity. We don’t run a singer size duct we start with the maximum CMF needed in the main trunk and reduce accordingly. Say you have a 4 ton unit that equals 400 CFM per ton 4 X 400 = 1600 CFM if we had to directions we would use 2 main trunks = 800 CFM each @ .10” of sp = 14” supply each then we reduce from there depending on the room size and load 12” = 600 CFM 10” = 400 cfm = 10” 200 CFM = 8” 100 CFM= 6” all at .10” of SP if you use this design everything works perfect. Put dampers at every Y and you will be able to balance the system no big deal. Once thats all done you design your return to .08” of static pressure install 2 returns and you will have a very nice system without having to buy gadgets

@justinballard7242 2 года назад

Mini splits ftw

@zachhansel361 2 года назад

Your demonstration with the water is not pressurized. Duct would pressurize and not distribute as demonstrated. People don’t put dampers in and think you are going to fix anything. You most likely will end up restricting to much air causing costly repairs.

@stickmanmob 2 года назад

The water is being pushed by gravity. There is still pressure, just not a lot, hence being a scale model. With enough pressure, any amount of any sized holes would all be flowing at the maximum rate. If you cannot increase the pressure going into the system i.e. upgrading the air handler, then you need to increase the pressure by restricting the flow out of the holes.

@HugeWolf1 2 года назад

Too bad you didn't talk about smart vents.

@sallyhansen5350 2 года назад

Can u sing?

@donc-m4900 2 года назад

all electric heating. no ducks in the house. 🦆

@Bremend 2 года назад

Heat pump or those coils that I swear barely get hot?

@freedomliberty7611 2 года назад

Most inefficient way to heat. Sucker

@jeepwild5772 2 года назад

First

@r3hab116 2 года назад

Congrats

@edwardlubin322 2 года назад

You win some sort of prize I guess.

@marekkrepa9982 2 года назад

To szybko na kolana I do roboty bo zaraz opadnie

@f1rstclass596 2 года назад

B4L4NCE!!!

@lewiskelly14 2 года назад

As usual, only half explained. TOH is always a half baked job.

@harman22595 3 месяца назад

sir, one thing to ask please reply, there is one thing called cross flow fan like one ac blower fan i have a idea to implement cutting this into half and fix one side to motor in a way that it can withstand on motor shaft without fixing the other side and rotate it reverse will it give air from inside the hole in center to out side, so that i can fix to pipe to make air flow edit: i wish you understand what i want to say + (-ve) |----------------------------------------------------------------------| open from this side |-----------------| |----------------------------------------------------------------------| | |===----------------------------------------------------------------------| ➡➡➡ |-----------------| |----------------------------------------------------------------------| - (+ve) |--------------------------------------------------------------------- | and air from these arrow to pipe to go further