HVAC Diagnostic Static Pressure Measurements

Link this post to advocacy through ASHRAE, The American Society of Heating, Refrigerating and Air-Conditioning Engineers. At ASHRAE I belong to one Technical Committee, TC 5.2, Duct Design, where I complain against prevailing cheap and poor design of residential HVAC air ducts. As a contractor I tear apart and reimagine some really-awful ductwork hacked in place by "professional" installers seemingly in compliance with the default rule book delegated to ACCA, Air Conditioning Contractors of America. I want superseding, better instruction, to be found at ASHRAE. Absent this improvement I will continue to practice better work as example to others. On this path I must be able to prove the better value of my alternatives, in a growing body of before and after HVAC measurements by simple manometer measurements of system pressures. Collect relevant blog posts by applying Label: HVAC Duct Design

Google the Subject of my proof quest:

HVAC Diagnostic Static Pressure Measurements

Google AI says:

Static pressure measurements in HVAC systems are crucial for diagnostics and ensuring optimal performance. They help identify potential issues like airflow restrictions, undersized ductwork, or dirty filters, which can impact efficiency and comfort. Technicians use manometers, which are pressure-measuring devices, to measure static pressure at various points in the system, such as before and after the air handler, the coil, and the filter. 

This is incorrect only in the mention of detecting a dirty filter.  Any sensible person will replace a filter on-schedule or upon dirtiness observation. The statement is deficient in not mentioning detection of possible fouling of the secondary heat exchanger in a high-efficiency gas furnace.

I have known that a major purpose of the measurements is to evaluate crummy HVAC ducts, and then to celebrate improvements made. Unfortunately I have been slow to accumulate measurement sets in a way that is sensible, recording measurements both before and after improvements made. 

I will quickly learn in a small sampling of customer homes that meaningful measurements identifying good or problematic HVAC duct design are very easy and unambiguous. They are for the purposes I imagine, just confirming my common sense about duct design. Measurements are not for a silly purpose of "measuring" blower flow rate. Rather, they are just design and construction quality documentation. Want least flow resistances rather independent of construction cost.

Find an appropriate graphic by search: 

graphic: a typical HVAC air duct arrangement and gage static pressure measurements

Credit this to energystar.gov

Label the gage pressure sample points as:

P1: Return, before filter box.

P2: Blower suction, after filter box.

P3: Heat Exchanger, wall at exit, if there is separate cooling heat exchange. Else this is at the  Supply Plenum,

P4: (Or P3) Supply Plenum

By themselves, P1 and P3 (or P4) are measurements of builder variables at hand: efficient design of the Return Ducts and Supply Ducts. P1 and P3 (or P4) should be very small numbers., demanded for everyone. Small numbers will correspond to quiet operation, best observed and judged directly.

P2 should be a very small nunber, except with fouling of the air filter, not a builder issue. Demand biggest/ best filtration for everyone.

The blower and heat exchanger investment is a builder and buyer choice not measurable by manometer. Higher efficiency in a gas furnace with secondary heat exchange fouled by cheap or none filtration, becomes a bad choice surely evident to the builder up-front.

Customer Rae, Goodman Furnace, Upflow, With Air Conditioning:

Good duct design in a home with already-existing supply registers is simply the use of the largest-size steel pipes that are available in branching to final register-size pipes.  Keep air guided and moving at similar velocity everywhere.  Allocate registers to ducts such that register air flow velocities are equal.

Here is my measurements setup for customer Rae with greatly-improved HVAC ducting enabled by demolition of a three-stories chimney. Learn: why should one demolish a condemned, inactive chimney? The chimney chase closed below-attic is now occupied by round ducts mainly the 12" return path from the upper floor here seen atop a collector box, instrumented with tap P1. Here label four static pressure values that are exemplary for most HVAC with separate exchangers for heating and cooling.

Good furnace mechanics are taught that for every well-running furnace, gage static pressure downstream of the furnace heat exchanger shall be less than 0.5 inch H2O. Foolish mechanics conflate this pressure, related to gas combustion conditions vs. atmosphere, to value P3 - P2, stupidly called Total External Static Pressure, a phrase unrelated to science in Bernoulli Principle. Wikipedia lists Static Pressure. but does not allow the unscientific phrase.

Delta pressure across the air filter is the best indicator of .air flow rate achieved by the blower. Want that to be a maximum. For comparisons, wish to find that every customer has the same superior air filter, Honeywell 5x25

Note that blower air flow rate is a default maximum in-common for many furnace manufacturers. Manufacturers discourage making non-default settings. Recorded static pressures for many furnaces will be familiar, comparable, not mysterious.

Here is the Rae table of gage pressure measurements and some computed differential pressures:

Wonder whether P1 and P4 are as small as they can be. They are reasonably small numbers, judging by other measurements reported here. Be concerned about Blower/HX Delta very high at 0.9 inch H20. Expect readings less than 0.5 in H2O. Suspect fouling of the secondary heat exchanger,  a risk/ cost of choosing a high-efficiency gas furnace  then operated for many years without a good air filter. Here is a Google Doc of the AI Overview of topic: clean the secondary heat exchanger of a high efficiency gas furnace, And here is the YouTube video of the cleaning cited, upon a Goodman furnace:  

https://youtu.be/xg0UliKF8vc

See that with unusual multiple return air paths, interior door positions matter. Should all interior doors be open. or closed? Can there be a standard set of home conditions? 

Gage static pressure values P1 and P4 by themselves have important meaning about duct flow resistance since they are uncoupled.  P1 is a  measure of return-air  flow resistance from house interior space up to the air filter. P4 is a measure of flow resistance to house interior space, from the final heat exchanger egress. Supply ducts have a bit more flow resistance than return ducts. Good design has the supply and return resistances equal and smallest-possible.

Customer Meyer, Goodman Furnace, Upflow, With Air Conditioning:

Here is a table of static pressures for customer Meyer, reimagined ducts well-documented in this blog post:

See that P3 - P2 is 0.8 inch H2O, exceeding an expected value near 0.5 inch H2O. Wonder if this is due to fouling of the secondary heat exchanger, where the furnace was operated for years without an air filter.

Looking at P1 and P4 as indicators of ducts return resistance and supply resistance respectively, see that supply resistance is double that of return resistance, and both are acceptably small.

My Home Goodman Downflow. Without Air Conditioning:

Here is a table of gage pressures and differentials for my home, 

Looking at P1 and P3 as indicators respectively, of return ducts and supply ducts flow resistance, see that returns are over-sized. The supply ducts are complex and long, with above-average but acceptable flow resistance.

Homes with heat pump HVAC will also have just three pressures sampled. Hope that in retrofit of a heat pump, ducts are reimagined and replaced.

Leet Carrier Upflow, 7/18/2025

An ideal upflow arrangement, with intelligent, biggest-possible flexible ducts. 

This is not the work of the original furnace installer.

10/5/2014 

The homeowner complained of loud furnace noise. I found, and fixed, this. The repair included reimagining all supply and return ducts in the crawl space. Such service is possible because I can rely on the design and build of an excellent sheetmetal shop. Nonsense must be avoided somehow.

Here is the job photo album:

Furnace Plena and Flex Duct Innovation, Multnomah Village

At 11/25/2025 upon finding a nice comment to this post, edit this job photo album, brightening all photos. I wish iPhone photos by default were not so dark. Know that much of the value I share is in a reader taking the time  to learn details of my consistent inventions.

Here mention the security achieved in flexible duct suspension from overhead floor framing using hangers to wyes and other strong steel duct elements.

 

And another invention, insulative coating of the interior of steel duct elements to reduce swung thermal mass.

10/25/2014

See wye trees that replaced an absurd Medusa D-box. Avoid turbulence everywhere, with steady-velocity guided flow.

See P1, understandably tiny return flow resistance from a large floor register directly-above. . See P4, a modest 0.21 supply ducts flow resistance. See suspiciously small air filter delta; perhaps there is something wrong with P2 location vs a turning vane. Someday wish to relocate P2 closer to the air filter. This furnace runs so very quiet. Think it is at lower blower RPM. P3 leaving the furnace is watched to be near 0.5 in H2O, and is much less.

Martinez Heat Pump Furnace Pressures and Error Discovery

Surprise! 

Here is all-electric HVAC, a heat pump furnace with beautiful cabinet simplicity.

And, surprise again to find that lofty heat pump installers can be stupid. A hack-in air filter slot does not support air filtration.

See the absurd return air path at the P2 probe half the height of the air filter slot. All return-path cabinetry cut into the furnace LHS wall must be replaced, including a horizontal proper air filter 20x25x5 and a big turning box with much taller side cutout of the furnace wall..

A 12" x 20" x 1" filter propped upright, is freely bypassed.

See that furnace and heat exchanger delta-P, P3 -P2, is quite large,  perhaps associated with heat exchanger fouling.  Perhaps a heat pump heat echanger is very unlike that of a 

 

HVAC ducts are very efficient:

P1 is the resistance in return ducts, -0.20 in H2O. 

P3 is the resistance in supply ducts, -0.15 in H2O. 

Here is my plan for improving Martinez return air ducts:

(Wait to do this in September 2025, when A/C won't be missed for a few days.)

Return air flow resistance will be reduced by a factor of four, a decrease of about 0.5 in H2O of static pressure measurement. The furnace blower will run much quieter and at less cost. The new  filter will at last be protective of the heat exchanger. Inquire whether the heat exchanger should and could be cleaned.

Reject cost/ benefit of a rounded, lined turning plenum with turning vanes (Leet). No other ducts are lined. This follows the example of Rae. The found return path area is doubled, and there is a proper filter box. The side opening into the furnace is doubled in size. Inquire with Rheem as to recommended furnace side cutout markings and size.

The turning box and filter box will be 3/4” above the floor. vs. found down box 66” tall and 2 3/4” above the floor.Combined height of the down box and filter box will be 68”.

Customer Menezes, Bryant High Efficiency Gas Furnace, Downflow. With Air Conditioning:

Here is a first instance of observation in both cooling and heating modes. Shifts in location of pressure drop are surprising, rather small, and real. More energy is needed to move cold air into supply ducts in cooling mode. Like the Leet excellent Carrier gas furnace, operation is surprisingly quiet, probably with less energy applied at the blower and longer cycle run times. Get what you pay for.

On-site, we talked about a hostile crawl space. There is some evidence in the static pressure measurements that supply ducts were installed with care. Still, I wish to inspect the crawl space someday.

Cautions Against Mis-Wiring of GFCI Outlets

 Wonder why GFCI outlets by Eaton and Leviton are packaged and labeled differently. Find this familiar and invariant  adhesive tape over the Load terminals of a Leviton GFCI. 

These instructions inside the Eaton outlet packaging are unhelpful to understanding the intended wiring arrangement. 

This is the Leviton GFCI powering a lamp, with correct wiring and normal function. The fairly-visible square green LED is redundant indication of the normal function.

"American" brands Leviton and Eaton share a deficiency that gravity must be turned to advantage to engage wires in floating grips. Better "Chinese" volunteered design has no-fail wire insertion through guide holes.

Eaton outlets have no instructions at all. 

Commonsense in the following rules argues against need of instructions: 

All GFCI outlets have these functional features:

• The outlet will not function at all if miswiring has the (single) hot lead attached to LOAD side instead of LINE. The reset button then does nothing. There are no LED indications.
• Upon trip, the outlet and all outlets daisy-chained from LOAD terminals are dead.
• Outlets daisy-chained from LEAD terminals are immune to GFCI trip, not protected. Perhaps half of circumstances are with want of this.  A GFCI outlet may be in a long daisy chain, not visible or even imagined, at a scene of frustration. It is bad practice if a device failure is caused by another device. Let every needed GFCI outlet be independent. 
• Another half of GFCI wiring circumstances has one GFCI protecting very-nearby other non-GFCI outlets, out of foolish economy, passing from GFCI LEAD terminals.

Yet, not-thoughtful installations where daisy chains branch loads to include lights, fans, dimmers, and more, may be dysfunctional, perhaps completely denying GFCI service..

For functionality, of all brands, I prefer Eaton.

Eaton is unique in having a bright red LED illumination at an edge of the RESET button. A small red LED is said to immuminate with device failure. For all other brands the small LED in green denotes proper service. The Eaton illuminations are more thoughtful.

Trip-Tested Eaton

Corner, tiny green indications of correct function are kind of silly. They are easily obscured by a cord plug.

Yellow tape over LOAD terminals does make sense. Daisy-chained outlets will by preference be strung from GFCI LEAD terminals. A string continuing via LOAD terminals does not miss protection by the GFCI outlet, the implication of the warning tape.

While all outlets now sold in USA are made in China, we will have no loyalty to USA brands Eaton and Leviton, then open-minded to all other brands imported from China. We expect to pay no premium for a "USA" brand not made in USA. At May, 2025, these other well-made brands are found at Amazon: Amazon Basics, ELEGRP, XIMAOESE and GreenCycle, cutting by half, historic prices of about twenty dollars per outlet. Tarriffs have no USA manufacturing to protect against global manufacturing cost difference arbitrage, a corrupt practice hurtful to workers. I have bought one each of all other brands, at Amazon, and find inadequate instruction against "miswiring" for all.   XIMAOESE and GreenCycle are exceptional in including the cautionary yellow tape of Leviton, now fully guarding against additional outlet connections daisy-chained through the LOAD terminals. At GreenCycle, I lose patience with all Chinese direct-sale offerings at Amazon. Be angry that market-flooding by China acts to destroy USA device brands, where we lose control of features. Be more angry that for the past fifty years, tax policy encouraged USA brands of all kinds, to end USA production.

The GreenCycle Ground terminal requires bending around the screw, a now-ancient and hated feature of outlets. Want straight insertion and space for bonding more than one ground wire. With GreenCycle, the green LED is on even after test-tripping. Want only red LEDs, indicating a tripped condition.

All GFCI outlets observed, when viewed as smiley faces, have ground terminals at the bottom. Since it matters very much to know which set of power terminals is Line for Hot connection, and backsides are hard to read, there must be consistency that Line is the upper set, as with current China production for both Eaton and Leviton. Instead there is absolute inconsistency. All knock-off brands made in China for direct sale as with Amazon, have Line terminals as the lower set. This is absurd and unacceptable. Buyers will presume that found wires undisturbed will accept a replacement outlet.

Repair of a Leaking Attic High Vent, Employing A Roof Penetration Adapter

This post of an action in 2016 is important in a Year-2025 campaign for broad employment of "roof penetration adapters" in residential roofing. Click the hyperlink to find a reverse chronology of all of my writing on this subject, in this blog.

Clarification is needed, whether penretration adapters are needed at attic high vent caps. They do have virtue. Please read on.

Here is a leaking condition that had recurred about once a year when high winds and driving wind would create a siphon under an attic high vent:

March 13, 2016

See that this attic vent was blindly cut in by roofers, without awareness of roof joist locations, as a new requirement on a home built in 1970. It would not have happened with a shingle tear-off.

A new problem was introduced in a re-roof, with cap misalignment from the shingle and sheathing cuts.

There are solutions against these misalignments. Immediately defy the siphon by stuffing a shingle bridge under the roof cap.

Better with a new venting opportunity on an already-shingled roof, let the vent locations be piloted from within the attic. Let all holes be circular, cut from the roof about the pilot hole. Insert a penetration adapter then to divert water flowing down-roof. Thereafter in a tear-off, center the adapter on the roof cut.

An imperative of easy and safe freedom in-attic to place high vent pilot holes would have been served by my self-funded campaign of Mandatory Attic Access Walkways. Know that vents clog over time from the inside. Circular high vents might have more promise of long unobstructed service, than roof-peak slots. A high vent cap should be easily removable for cleaning, from the roof,  without pulling any shingle nails.

Get the idea of the new-roof high vent installation process from rework of a found 4"  roof cap, now to serve a strong kitchen exhaust fan with 7" ducts. My roof adapter has bore 7 1/2" ID, 1 1/2" tall, formed of spun aluminum. The available roof cap is Famco 8". The 2x8 board has deck screws that when worked into composition shingles about the pilot screw will enable a well-defined sheathing cut by Sawzall. This is the same-size adapter plate that was tried by a very competent roofer under my instruction, to fix my leaking roof high vent.

Construction Metals RV38 Vent Cap Over Added 7.5” Roof Penetration Adapter

The penetration adapter is one shingle row deeper than the roof cap. A lower shingle bridge stops possibility of siphon action, even without the penetration adapter. The penetration adapter is redundant except as a can’t fail locator of the sheathing and shingle cuts. The adapter is locked in posution where it is attached to a duct. For a non-ducted roof cap, set it permanently upon the sheathing cut using upper-edge screws or nails. With a firm-set adapter rim, cut replacement composition shingles by stabbing-around with an awl; then breaking away the divots.

A further virtue of the adapter is in allowing a powered fan to be set in place of a static vent, without disturbing roof shingles, tiles or metal sheeting. Want all powered fans to be freely removable for service or replacement, without disturbing roofing.

The leaking vent was repaired including employment of a 7 1/2” spun-aluminum duct penetration adapter. Opportunity of better alignment with the roof cut was missed, and the use of shingle bridges is unknown. There has been no return of leaking. If respected, this will be an example to a roofer someday of ensuring alignment with the sheathing cut. Wish that better alignment of the adapter will be chosen. Wish the cut of plywood ang skip sheathing had not been excessive. Sharp corners are stress risers for lumber splitting.

We find that very many bath fans and kitchen exhaust fans are badly, even dangerously ducted. In any existing home the rather frequent retrofit of a new fan is not subject to building codes/ permitting review. Awful access to the attic contributes to the problem. I see this as a unique engineer/ inventor/ contractor/ technical writer. From age 60 twenty years ago, I have been a general contractor focused mainly on attics and crawl spaces. I know that dirty, awful work, delegated, is without learning and practice with ever-better materials, methods and procedures. I demand that practice of myself and am unaware of another like-minded attics person anywhere.

A roof penetration adapter is very useful when a roof cap is served by a through-roof duct. We shall want that all roof caps and roof-top powered fans are removable for service or replacement, without need af attic entry.

A ducted roof cap with a stem invites others to bond the duct to the cap; then removable only with attic entry. My preference is that ducts shall be galvanized steel "warm air" pipes. The crimped end is upward toward the roof, engaging often as an elbow, to full, tight penetration of the adapter plafe throat. Slight maneuvering of the adapter in a reroof shall not decouple the duct somehow strapped-up.

There shall not be compromise aiming of a duct pipe or flimsy plastic thing toward an existing attic high vent cap. There shall be no capping over framing or roof sheathing at a static vent cap, with a common "duct starter" plate, the usual practice wrongly taught to weatherization contractors.

 At 2025 there is a wrongful trend to offer duct-served roof caps only with long stems that reach into the attic. There is at least one cap manufacturer thinking like me.

 InOvate/ BetterVenting 

Product RoofNeck

Employed with 4" stemless caps for clothes dryer ducting. This is a rolled-in pipe length necessarily reaching both directions from the plate.

Where the adapter has a neck penetrating roof sheathing, it is securely linked to the roof cut. For an adapter without sheathing penetration, as I  offer of spun aluminum, some other means must index the plate to the duct. A crimped pipe end protruding through sheathing, works. I do not prefer an adapter with neck. It is so very much harder to interleave with shingles, requiring more nail pulling in an insertion through already-placed shingles.

Want adapter plates with a simple neck at least 1 1/4" tall, as formable in stamping of aluminum. If a short neck protruding downward is needed as a location index, let it be a separate galvanized steel pipe length, crimped end, inserted from the attic. The stamped upper protrusion has needs of leak-free permanence.

Who do you call, for through-roof ventilation exhaust ducting?

Who do you call, for through-roof ventilation exhaust ducting ?

A Google AI Overview answer is:

For through-roof ventilation exhaust ducting, you should call a licensed roofing contractor. They have the expertise and experience to properly install ventilation systems on your roof, including assessing your needs, choosing the right type of vent, and ensuring it's installed correctly to prevent leaks.

If that were true, roofers would be constantly willing to work in attics to create the majority of that ducting and the installation of the fan appliances served. Roofers do not have this interest or capability.

Consider my need of a kitchen exhaust fan in the major remodel of the kitchen of the home I own.

I chose a Panasonic in-line fan, pivoting from flooring over thorough R49 insulation with only a small-bend 6" warm air elbow to complete the path through-roof. Here I drilled a pilot hole through-roof at the center of a tracing of the placed elbow. Duct completion is in several traverses between roof and attic, enabled by a strong attic ladder, and by good lighting and flooring in the attic

Cut through shingles with a wood block propelling sharp deck screws, preserving a hole saw. Drill a hole starter and complete the cut with a sawzall. Pry shingles and pull nails as needed. Collect wood debris in the attic upon a sheet.

12/5/2018

Here is the fan, ready-to-use.

My vast attic flooring is useful. It adds to insulation value and serves as the top element of extremely strong box beams of the 12" thickness floor over the remodeled kitchen.

The insulation is protected forever.

I had to anticipate all of this in placing the register and duct from the kitchen ceiling over the electric (not gas!) stove.

At much of a four-foot periphery the insulation is protected just by being off-path. See top-layer R30 Rockwool insulation except R30 fiberglass at the extreme periphery, accommodating plywood attic ventilation inlet baffles.

9/27/2018

See the kitchen fan register in-line with an operable window, over the kitchen stove. Upon a steamy or stinky cooking adventure, lift the window a bit or a lot, and turn on the fan. The view is from the archway entering the kitchen from the living room. The fan switch is the right-most of a 4-gang switch group. The lighting constellation chosen here is Passing Through,  4-Way switched at each of the three entries.

In this, my now-modern and clever 1955 home, I could not imagine calling a Licensed Roofer, for greater competence at the through-roof ducting of the kitchen fan. Roofers by my experience see an attic as merely a trash heap. They will not go there. Roofers will benefit in a new regime where other Trades, or a general contractor, will just stay out of their way. And, that is what I have practiced here.

This illustrates a customer installation of kitchen exhaust ducting similar to my own. See that the ideal location of the penetration adapter is in hinging at the high end upon the roofing membrane. That is one shingle-layer deeper than a common roof cap. The better roof cap is minimally tucked under shingles. The screwed-down roof cap safely anchors disturbed surrounding shingles against driving wind and rain.

As a inventive Weatherization Contractor and General Contractor, I almost always confront really-awful ducting of bath and kitchen exhaust fans surely not the work of roofers. I am not taught to call a roofer, but to do what I can, myself. With bath fan ducts, the best and awful practice of weatherization contractors is to just plug the plastic or flexible-aluminum found duct, to a 4" take-off stabbed into a plate that covers a found roof high vent. I know better. That installation then lacks a backflow check and diminishes the needed attic ventilation. The duct probably obstructive of discharge from a crummy fan that is only a noise-maker, continues to do harm.

Here is a photo album sampling my jobs employing penetration adapters, in chronological order, showing evolution of methods.

Search  Label: Roof Penetration Adapter , at this blog, and find posts including these:

Roof Caps For Bath and Kitchen Exhaust Ducts  (January 15, 2017)

Note then this post describing the shingle-over of my roof in Spring 2023, being the roofer confronting this roof cap. I could venture into the attic, but there is no need:

 Roof Penetration Adapters and a Composition Shingle Overlay  (April  3, 2024)

Turn out four gasketed deck screws to reveal the roof closure with a 6" penetration adapter and its' transferred flapper, riveted to the adapter rim.

With little nibbling of new shingles, the rain barrier  hinges down, perfectly aligned with and coupled to the duct and fan below.

There was the same accurate simplicity at three 4" plastic Air Vent caps without stems.

Learn an important lesson. Lay down all covering shingle rows before screwing down the roof cap. The shingles will be more-strongly retained including fullest engagement of tar strips. Let the cap not be tucked under shingles anywhere if that is how it works out. Remember, the cap is only a rain cover. There is never a need to cut shingles as more than the circular hole. Shingle material lapping over the top of the roof cap has no purpose. It is not more pretty.

What, really, is needed in a roof cap?

code requirements for ducting a bath fan through a roof

Google AI Overview: 

when ducting a bathroom fan through a roof, the primary requirement is to exhaust the air directly outdoors, not into the attic or any other interior space, meaning the duct must be routed to the exterior of the building and terminate on the roof.

There is reference to International Residential Code (IRC) Chapter 15, Exhaust Systems.

code requirements for ducting a kitchen fan through a roof

Google AI Overview:

According to most building codes, when ducting a kitchen fan through a roof, the exhaust duct must terminate at least 12 inches above the roof surface, with some regions requiring even greater heights to prevent snow buildup, and the ductwork should be positioned at least 18 inches away from the roof surface where it attaches to the fan; the fan discharge itself should be at least 40 inches away from the roof surface.

This is surprising in the matter of elevation at discharge!   And, never met in my discoveries. Who offers such a discharge path above the roof? It seems to be concerned about flame in a grease fire, or discharge burial under snow.

I find nothing offered, in this Google search: image: 12" tall kitchen exhaust roof cap

Smarter now, I could replace the squat Famco cap with this: 

Goose Neck Exhaust Roof Vent – Painted Famco, $99.95. 

The lesser flow resistance makes sense. Nibble out the stem and flapper, or convince Famco to offer separate cap without stem, and flappered penetration adapter.

Want the elevated discharge for a bath fan too, to tolerate snow.

Let even a not-ducted attic ventilation high vent be only a rain cover. Where placement is set with a penetration adapter, avoid misalignment of the sheathing cut and the cap.

Now move on to report an incident that inspires this post:

Violence against bath fan ducts in my row home residence, July 17, 2024!

In this job photo album, I share the awful and typical conditions of fans and ducting that I found and fixed in a now-pretty and useful attic.

On July 17, 2024, the two bath fan roof caps were ripped off, leaving broken ducts to dump moist air into the attic, blackening the roof sheathing.

We were not consulted We were not informed.

New steel caps with manually-crimped stems were left to again defy roofers, at the next roofing replacement, if we were smart enough to reattach the ducts..

10/30/2024

The steel ducts with new elbows are now screwed and taped to the foolish roof cap stems. At next reroof, workers might curse the now-captured roof caps, again breaking the ducts in refusal to enter the attic.

See that this space directly off the  wonderful attic ladder is the convenient repository of long ducts and other sheet metal I keep in reserve for my unique A-rated business of Attic Access.

With this post and that album, please understand that a roofing company is not the superior owner of well-performing bath fan ducts, entitled to demolish them for no apparent reason and without notice. The roofing repair company of this incident is identified as  NW Roofing. We must learn whether NW Roofing routinely breaks ducts bonded to roof caps, without thought of repair. In most cases, attics are hostile of access, and in many there are no safe walkways to points where it is known that service will be needed at intervals not longer than 25 years. See my proposal that attic access walkways shall be mandatory to expected service points.

This blog, Sunday, October 30, 2016

Mandatory Attic Access Walkways

At my own expense I defended ten thoughtful proposed revisions to 2016 International Energy Conservation Code. All ten were unanimously disapproved in a codes process rigged by National Association of Home Builders. In a bad regime of service access, it is very important that roofers shall not be required to enter attics. Roofers must come to understand the impossibility of their responsibility for and superiority over ducts. With roof penetration adapters and their permanent attachment to ducts, roofers may do only what they do best.

As a unique and valuable weatherization contractor/ engineer/ inventor, age 80, I have given much exemplary service to existing homes for twenty years, in metro Portland, Oregon. Here is the job album of one good example in SW Portland, with mending of awful bath fans and a kitchen microwave exhaust without ducting even to the attic. Safe, lighted access and removal of interfering and not-needed beams were  imperative. Awful, dangerous conditions in a home often need considerable investment to do right.

Job Album C-L Attic Access, November-December 2016.

 

I know of no one else on Earth doing the important work I inspire. I need allies including most-competent roofing companies. Specifically at January 2025, I need the support of Pacific West Roofing, the installer of the current roofing of the townhouse complex where I live, and where my penetration adapters known to them, were misunderstood and violently discarded. I ask that Pacific West Roofing shall support my timely product improvement requests to roof cap manufacturers Famco and BetterVenting. Where BetterVenting begins with a focus on the small market of through-attic clothes dryer ducts, they shall know that dryer caps must be cleaned often, off-roof. BetterVenting (Inovate) offers an adapter similar to mine, called RoofNeck. They don't seem to value the device as a water barrier or as an asset to cap cleaning. Dryer ducts must be thoroughly cleaned very often, more easily in soaking, off-roof.

BetterVenting RoofNeck with smallest-possible sheathing cut:

Install above or below the roof deck. 

The plate is too small to mend sheathing hacks or misalignment with shingle patterns. The neck at 4 1/8" ID does not securely engage with warm-air steel ducting 4" OD.

The downward neck invites capture in the attic, which is OK only if  this is a permanent part of the roof. Atttachment holes should then be only at the top edge, allowing hinging tuck of membrane and shingles in a reroof..

BetterVenting imagines a dryer cap thoroughly bound by surrounding shingles. If there is a RoofNeck here, it is not being employed to best advantage.

I have learned that the best use of a cap primarily a rain cover, is to anchor the surrounding shingles, with just four gasketed deck screws. Don't be breaking tar strips and pulling nails to clean a cap/.screen/ backflow flapper.

At 2/12/2025, Google this:

penetration adapter for ducted vents of a house roof   

Find some foolishness in caps with stem jabbing through-roof, and this:

Roof Cap Vent Adapter · Metal Ducting · Galvanized · 6" (RVA6) 

By PrimeSource Building Products

Dunn Lumber Store SKU

559176

Price at 8/22/2025: $16.40 plus shipping.

(Not an economical availability.)

Any local good sheetmetal shop can improve upon the Dunn cost and availability. Specify  stem ID that of standard HVAC round pipe. Custom-form the stem as a  weldment of strip 3" wide. Roll-form the stem centered in the hole-cut plate. Let the plate be round or square at say 3x stem diameter, or maybe stem diameter plus 8". Any economical producer would set a plate shape standard. A plate-centered 3" stem would pilot both the round minimum sheathing cut, and divert water flow under the roof cap.

Better but without the piloting in roof sheathing, form penetration adapters by stamping aluminum plate to form a 1 1/2" upward stem. Let there be competition for least-cost distribution of a penetration adapter for every roof cap. Let the penetration adapter have a hinged flapper for backflow prevention even at high statc vents, to combat embers in wildfires. Just get on with smartness and an uncoupling of roofers from needs of attic entry.