Questions tagged [ducts]

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General Idea on Sizing Plenum

What are some general design theories (not formulas) for sizing a plenum or main distribution box coming off of a typical residential furnace/AC unit? I'm not asking so much about systems with large ...
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44 views

Attic HVAC ducts are in the way. What should I do?

Just moved in to a new house back in September and I want to add some pendant lights in the kitchen. Went up into the attic and looked around... The main HVAC duct bisects the attic and I will have to ...
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4answers
10k views

How to fill / seal in-slab hvac ductwork?

My house is built on a slab. Within the slab are "channels" which act as ducts for the HVAC system. I assume it is partially lined with metal but based on photos from an HVAC-cleaner, it's hard to ...
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25 views

Popping sound coming from duct

Whenever the furnace is turned on or off, there’s a spot right below my bedroom floor where vent is, the duct would make a popping noise for about 5-10 minutes. Unfortunately the duct is not ...
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2answers
67 views

How big of a duct and grill do I need for a central cold air return on a 3 ton system?

What size grill and duct do I need for my cold air return to fit between wall studs in the following scenario? I have an open-air return in my basement mechanical room with no cold air return ducts or ...
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2answers
120 views

Do I need to seal the rotating seams of a duct elbow?

Kitchen range hood installation questions: Do I need to seal the points indicated by the arrows? Any opinions on mastic over foil tape? I have some 3M 3340 laying around. Can mastic be used inside ...
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2answers
54 views

Bathroom venting 2 in 1

I have Installation where I will use two bath fans. One in the half bath and toilet and sink the other outside where the shower will be. I would like to combine the two into 1 the outside the house
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0answers
43 views

HVAC duct issues

Purchased a home a few months ago that was gut rehabbed with new AC + furnace + ductwork and left vacant for a year. A few weeks after moving in I took a chandelier out of the ceiling in the dining ...
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1answer
123 views

What is the purpose of this metal piece?

Attached is pictures of my HVAC plenum, where it meets the ceiling. Recently I had water damage(from upstairs neighbor) and I had to replace entire ceiling. After new ceiling I see this gap (yellow ...
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1answer
70 views

How to avoid sealing duct joints inside walls?

I am trying to replace a very short amount of duct work for my range hood and am having a bit of an issue figuring out how to seal/tape the joint between the 6" elbow duct and the wall cap. ...
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1answer
128 views

How do I fix a loud intake vent?

In the master bedroom, there is one of four intake vents in the house, and this particular one is very loud. Our house has two vertical air shafts that run parallel to each other, one for supply and ...
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1answer
32 views

Size of a return duct

because I have a large bedroom, I’m adding another return duct which I will put on the ceiling against the wall. It's a 15’ ceiling and I want to get the trapped hot air out. Now, I was thinking of ...
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1answer
44 views

How to seal the frayed fiberglass border of internal duct insulation in the middle of a duct

I had to remove the bottom foot of internal duct insulation touching the ground due to sewage backup. Now that there is a frayed edge of internal insulation inside the ductwork with the remaining ...
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1answer
55 views

How to remove slip and drive duct cleat when there is no room on the sides

I need to remove a 2-foot section of ductwork that got flooded so that I can rip out the internal insulation, but I don't see an easy way to remove the drive cleat since there is only about a 3/4"...
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1answer
762 views

Can a motorized damper be installed inside existing ductwork?

My HVAC system consists of a fan, furnace, compressor-driven AC, and evaporative cooler. The problem is that there is a large air volume used only by the evaporative cooler that is generating a lot of ...
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0answers
18 views

Replacing flexible HVAC duct with rigid metal ones

I am in the process of replacing some flexible HVAC ducting with rigid metal ducts (mostly because I wanted to deal with poorly done and leaky registers, but also because I just do not like the ...
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0answers
64 views

Is it code to create a return vent that goes directly to a furnace room from the floor above

My first-floor apartment (in a townhouse/brownstone) didn't have a return air duct installed and is instead just sucking in air from the boiler room with a large open return. The architectural plans ...
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2answers
491 views

What's the minimum clearance from drywall when installing rigid duct work?

What's the minimum clearance required when installing rigid duct work on vertical walls with drywall and 2x2 framing. If I don't install drywall behind the rigid duct work for which there's only 1/2&...
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2answers
117 views

How do I re-route this wall register to exit a cabinet base?

I am redoing our kitchen, and adding more cabinets. This register ended up behind 2 cabinets. How should I route the duct to 1 or 2 toe kick vents? Do I need duct work under the cabinet, or can I just ...
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29 views

Casement Windows: Install Thru Wall A/C Indoors & Exhaust with Ducting

A family member has a business in a century-old building that only has industrial casement, awning, and pivot windows. There's no central A/C & a mini-split can't be hung outside the building. The ...
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3answers
4k views

How do you remove and re-install Register Duct Boot?

Is it possible to remove and replace this register duct boot without screwing up the dry wall around it? Large Images: https://imgur.com/a/lh9HIt2
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0answers
43 views

How to replace a supply plenum box with a blower sitting on top of it

I'll probably hire a professional, but I was curious if it's easy to replace a supply plenum box that already has a blower sitting on top of it. How would that be replaced, do you have to keep it ...
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2answers
1k views

How do I patch a subfloor over a return duct cavity

I need to patch these holes in the subfloor where the vents are. These holes are from a return vent that is being moved, the joist cavity below these holes is a return duct. I'm assuming using ...
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1answer
46 views

Is there a reason to choose taped fiberglass bats vs fiberglass tubes when insulating heating ducts?

I'm going to insulate the 6" round metal heating ducts in my crawlspace, and I have pretty good access. It's the SF bay area, so it doesn't get very cold. Is there a reason to choose taped ...
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1answer
185 views

Axial or centrifugal fan for short run out of kitchen?

I'm researching replacements for a broken extractor fan in my kitchen. It is wall mounted and runs through the wall straight outside, no long ducting involved. The current (broken) fan is the ...
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3answers
83k views

Why am I finding condensation in my dryer?

I live in Houston, TX (Very Hot, Very Humid). In the summertime, my dryer is dripping with water, when not in use. I do not have overly excessive drying times. My dryer is vented via an unfortunate ...
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37 views

How to correct an old bathroom ceiling vent fan duct (or lack thereof) in an old 2 story house

I'm fixing up an old home, built in 1930s, renovated in 1980s that has a terrifying fire hazard of a bathroom light/vent fan/heater in the downstairs hall bathroom. When this old unit was removed, not ...
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1answer
71 views

Should a HVAC return be partially closed in proportion to already closed supply branch in basement?

I have damper installed for each supply branch for my basement. There are six supply lines (5" flex duct each) for just basement. It covers 1100 sq ft (includes 1 bed room and 1 bath) for a 3 ...
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1answer
223 views

HVAC turning off below 30 degrees

A bit of a long post but I've tried to be as specific as possible I had a new Goodman HVAC put in Dec 2016 (model GPG1430060M41AB). For the last nine weeks the system has been cutting out when the ...
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1answer
57 views

Would a ducted heat pump lose a lot of effeciency if the ducts are installed in an open crawlspace?

Currently I use a woodstove to heat my place (no ducts). I am thinking about installing an air-to-air ducted heat pump to heat my place. I am trying to figure out what are the important factors (in ...
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3answers
784 views

How should I repair a hole cut into a heating duct?

I found a large hole (~10cm x 10cm) cut into one of the HVAC ducts that supply the bedroom. It was cut between the duct and the joist and is not visible from the ground, I found it attempting to ...
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1answer
460 views

How to connect a semi rigid aluminum duct to a rigid aluminum duct

In a 4 story multi-owner house in Rotterdam, the Netherlands there is an 80mm semi-rigid aluminum duct like the one shown in the image below which contains the water heater exhaust of my neighbors who ...
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52 views

What is this duct part that was attached to a roof vent?

This plastic part was attached between the flexible duct and a roof vent. The vent was used for a bathroom exhaust fan. What is this part called, and what purpose does it serve? The roof vent was ...
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3answers
2k views

Is having a branch off the end of main heating HVAC duct bad and if so, why?

Question: Is having a branch off the end of main heating HVAC duct bad and if so, why? Background: A heating and cooling contractor sales representative came to my home today. He saw the situation ...
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2answers
173 views

Is there a reason to replace 50 year old metal ducting in the crawlspace with modern insulated flexible ducting?

My concern is heat loss in the chilly crawlspace. No AC here, only forced air gas furnace. The existing metal ducting in the crawl space is over 50 years but is intact. There is a very thin layer of ...
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1answer
65 views

My dryer isn't fully exhausting to the outside?

I recently bought a townhouse which has laundry in the finished basement. I noticed that our clothes took a bit more than an hour to dry in the dryer, so I wondered if there were any lint blockages. I ...
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3answers
55 views

Gas fired Forced-air furnace has a outlet grill in the mechanical room - can I remove it?

I just moved into a house with a gas fired forced-air furnace. Whenever I'm in the basement and the furnace is running I can hear a whistling noise coming from the mechanical room. I traced this sound ...
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1answer
107 views

Is this dryer vent installed correctly?

Should I add those vent straps? It seems pretty sturdy, but I want to be certain. Is it even in a good location on the wall? Everyone I spoke with said it looks fine, but still a little strange to me ...
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1answer
46 views

Should I remove abandoned cold air return trunk?

When the furnace was originally installed, the first floor of my house had four cold air returns, two each on the long walls. When the kitchen was renovated in 2015 (before I purchased the house) some ...
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2answers
124 views

How to fit portable air conditioner hoses through a too small wall vent

Our apartment doesn't have A/C, but we do have wall ports for a portable A/C unit. Unfortunately, I can't really fathom how I'm supposed to hook the hoses up to the wall vents. As you can see, the ...
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1answer
89 views

In Slab Duct Work - Concrete / Cinder Block

I have some weird and what I believe to be abnormal duct under my home. I recently installed a brand new HVAC system and it's not running or performing as desired. I believe I am losing a ton of ...
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1answer
167 views

Can a single 8" flex duct be split into a 5" flex and 7" flex?

Our house used to have a fur-down A/C unit that fed a series of rigid ducts made with duct board. We'd like to replace a vent in our bathroom (5' x 11') with a 5" flex duct. We'd like to ...
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1answer
56 views

How can I install ducts on a high place in a building where I can't put nails or screws and where I can't hold ducts to install them?

It's a building like that and we need to install ducts at where the red line is. There is no near balconies or windows to help me put the screws in the wall. The ladder can reach up to the blue line ...
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0answers
32 views

How do I shorten pre-installed ducts without cutting into the ceiling?

Upgrading a bathroom fan and I need room to convert a 3" duct to a 4" flapper on the fan (about 7" of length overall). The ductwork is rigid sheet metal and ran directly to the old fan. ...
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1answer
170 views

How can I prevent makeup air vents from exhausting conditioned air?

The utility room has two 8-10 inch ducts running to it from the exterior of the home. There are also three fireplaces in the home, and we have noticed that occasionally the house smells like smoke, ...
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1answer
74 views

What is this sealing material inside a duct collar?

Most of the duct dampers don't provide 100% seal from air flow. The below picture might be. I have collar with damper, But its just not enough to stop/bypass the air flow. what is this called in the ...
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2answers
88 views

One branch of my HVAC receives zero airflow, is there a design flaw with this layout?

Question: Why would the 6" duct (represented by the red X) produce almost zero airflow? I have a small piece of tissue attached to it to see that it's barely blowing anything. However, the blue ...
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2answers
1k views

How can I offset 6" ducting by just a few inches?

I am installing a range hood and due to a ceiling joist in the way, I have to offset the ducting going through the ceiling by about 3" from the center of the hood. I have to do this within about ...
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1answer
59 views

Does a vent register boot always has to be installed parallel to wall for a better air flow all around?

In my basement, I have a gas pipe (1" diameter) running between the joists. There is a reason why I have choose this cavity to run a supply line from where. But I am end up using a end boot ...
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1answer
121 views

How can I insulate a duct running through an unconditioned kneewall space?

Unfortunately, I have to run an 8 inch HVAC duct through an unconditioned kneewall attic in southern Ontario (climate zone 6). I am trying to decide between two options: Encapsulate duct with spray ...

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