British Columbia
WHERE EACH DIMENSION COMES FROM AND WHO CHECKS IT
A fitting can match its drawing exactly and still miss the opening if one number on that drawing was never checked on site.
Whoever takes a measurement is responsible for it, and whoever approves the shop drawing is responsible for the sizes on it. Field-verified dimensions are the ones someone measured on the building itself and marked as measured. Most custom fittings are built from a mix of design sizes, measured sizes, and an equipment maker's sizes. Mark which is which before Duct Duct Goose, or any fabricator, starts cutting. Then if a fitting misses, everyone already knows whose number was wrong.
Every size on a fitting order comes from one of four sources and ends up on one approved drawing. Knowing where a size came from tells you who should check it before the order goes in.
| Where the number comes from | Who checks it | What to do before you order |
|---|---|---|
| The engineer's or architect's drawing | The designer checks the design, and the contractor confirms the sizes on site | Measure the opening, or mark the size as taken from the drawing |
| Your crew's tape measure | Your company | Mark it as measured, with who measured it |
| Our field measure | Duct Duct Goose, for what our installer could see and reach | Tell us about any change planned after our visit |
| The equipment maker's drawing for one model | The maker checks its unit, and you check you've named the right model | Send the full model number and the maker's drawing |
| Our shop drawing, once you approve it | We build to it, and you check the sizes before you approve them | Check every size against your numbers before you sign |
A building is rarely built exactly as drawn. That gap is why a size measured on site and a size copied from a drawing carry different weight.
It comes from the engineer's or architect's drawings. If the building went up a little differently, a fitting made to this size follows the drawing and misses the opening. It's commonly used for new work, and checked on site once the opening is built.
Someone measured it on the building itself and marked it as measured. It costs a site visit, and it's the only size that shows what was built. It's commonly used for renovations, rooftop unit swaps, and any opening that already exists.
A drawing that says "verify in field" is asking for the second kind. How to measure ductwork for a custom fitting explains that note and how to take each size.
On most Canadian projects, the contractor confirms sizes on site, and the contract documents say so in a few places. Four of them matter when you order a custom fitting.
Since its 2020 edition, the contractor reviews the drawings to coordinate the work and reports any error it finds. If a size doesn't add up, report it in writing before anything is made.
Many Canadian project specs say the contractor's stamp certifies that field measurements were verified. If you stamp a fabricator's drawing, check its sizes against the site first.
Their review checks the design, not your measurements. If they approve a drawing with a wrong size, the contractor still pays to fix it.
Some public owners' duct specs say to build ductwork from field measurements, not from the drawings alone. If yours does and a fitting made only to the drawings misses, the remake isn't paid as an extra.
Your own sign-off on a fabricator's drawing starts a set of stages, and each one makes a late change cost more. They're laid out in what happens after shop drawing approval.
A size with its source written beside it settles most fit questions before they start. Some project specs already ask for field dimensions to be marked this way.
Mark each size you measured. Write "field verified" beside it, with the name of the person who measured it.
Mark the sizes copied from the design drawings. Add the drawing number and revision beside each one.
Name the equipment model for any size of unit sets. Give the full model number and attach the maker's drawing for that exact model.
Leave a size open if the site isn't ready. Say when it can be measured, and ask if that fitting can wait.
Check every size on the shop drawing before you approve it. Your approval tells the fabricator to build to those numbers.
Every size on the drawing says where it came from
A transition from an existing duct to a new unit, with each size tagged by its source.
Measured on site
Field verified, with the name of who measured it.
Copied from the design drawing
Drawing number and revision written beside it.
From the equipment maker
The maker's drawing for the exact model on order.
Still to be measured
Left open, with when it can be measured.
There's no single default for duct, so a size with no tolerance beside it leaves "close enough" to whoever reads the drawing. Write the tolerance you need beside any size that has to be exact.
| A size that often needs a tolerance | Why it matters | What to write beside it |
|---|---|---|
| A collar or end that slides into existing duct | Too big and it won't go in, too small and the joint leaks | Whether it may be smaller, larger, or neither, and by how many mm |
| A curb adapter that sits over an old curb | It has to clear the curb on every side without rocking | The curb's measured outside size, and the gap you want around it |
| A fitting that runs between two fixed points | Any extra length has nowhere to go | The measured distance, and whether a slip joint can take up the difference |
| A cut-out for a damper, access door, or grille | The part has to drop into the opening | The maker's cut-out size for that model |
Only you know how much room your opening leaves. A number on the drawing settles it before cutting, not after.
In duck, duck, goose, everyone in the circle knows who got picked, because they got tapped on the head. Every size on a fitting order needs the same one named person picked to check it. A size nobody picked goes to the fabricator unchecked, and the miss turns up at install.
| The mistake | What happens at install | What to do instead |
|---|---|---|
| Measuring a size off the PDF with a ruler | The drawing may not be to scale, so the fitting is made to a guess | Use the written dimensions, or measure on site |
| Passing a "verify in field" size to the fabricator without measuring it | It misses the opening if the building differs from the design | Measure it, or book a field measure |
| Measuring before the framing, beams, or equipment are in | A later trade moves the opening | Measure once the work around it is in place, or note what's still to come |
| Sending sizes from an old drawing revision | The fitting matches a design that has since changed | Give the revision letter with every size |
| Changing the rooftop unit model after the curb adapter is ordered | The new unit's base doesn't match the adapter | Send the new model number before the adapter is made |
| Approving a shop drawing without reading the sizes | A wrong size gets built, and the remake is your cost | Check each size against your notes before you sign |
This curb adapter order is an illustration, not a Duct Duct Goose job. Three sizes came from three sources, and only one was never checked.
| The size | Where it came from and who checked it | What it meant at install |
|---|---|---|
| The old curb's outside size | The contractor's site lead measured it and marked it field verified | It matched, because the number came from the roof itself |
| The new unit's base size | The maker's drawing for the model on the order | It matched the unit that arrived |
| Where the supply duct meets the adapter | Copied from the building's old mechanical drawing, never checked | A past renovation had moved the opening, so the connection missed |
The adapter matched the drawing the contractor approved, so the remake was the contractor's cost. A look at the supply opening from the ceiling below would have caught the one size nobody checked. Curb adapters like this one are part of our roof curbs and flashing work, made to the unit maker's sizes and your measured curb.
Every fitting we make starts from the numbers you send and the drawing you approve. These steps keep each size traced to where it came from.
We ask where each size came from. Measured on site, copied from a drawing, or set by a piece of equipment. If nobody can measure, we can quote a field measure as its own item.
We check equipment sizes against the maker's information for the exact model you name.
We plan the metal thickness and each bend before cutting, so the finished fitting matches your number.
You approve the shop drawing. Your approval tells us the sizes on it are the ones to build.
We re-check key sizes before a fitting leaves. If it misses the approved drawing, we fix or remake it at no charge.
Our custom duct fittings and HVAC ductwork fabrication pages show what we make from those approved sizes. Single fittings and full duct packages go through the same steps.
Who measured, and whether the site changed afterwards, decides whether the fit is on us. Everything else follows from those two facts.
Our installer measured the site, or the fitting doesn't match the drawing you approved. In both cases, if the mistake is ours, we fix or remake it at no charge.
A size came from someone else and wasn't checked, the site changed after it was measured, or the problem was hidden behind a wall. An exact copy of another maker's product isn't on us either, because we can't check the original's sizes.
If a fitting doesn't fit once it's on site, what happens when wrong parts are delivered walks through the first steps. When a field measure suits the job better than your own tape, supply only or supply and install shows how it's added to an order.
When a length can't be known until the duct is going up, a custom fitting may be the wrong answer. Round spiral duct can be cut to length on site, and we supply it. We'll say so, even when it means a smaller order for us.
Each item takes a minute, and together they leave no size without someone behind it. Tick them off before you send the request, not after the fabricator's drawing comes back.
The rest of a complete request is in what Duct Duct Goose needs to quote custom metalwork. More guides on measuring, scope, and the install sit in Field Measure, Fit and Installation.
Send clean drawings or a sketch with sizes, and say where each number came from. We'll tell you which sizes still need checking before anything is cut.
Standard ductwork and fittings price instantly on WebDuct, the online pricing and ordering portal, with a company account. Stainless, grease duct, installs, and other custom work start with a request or a call.
At Duct Duct Goose, we specialize in sheet metal fabrication and stainless steel services for commercial and industrial applications, including HVAC systems, ducts, and custom metalwork. Please note that we do not offer services for automotive-related projects, such as vehicle parts, repairs, or modifications.
