Fig 1

The Burt Manufacturing CO., manufactures of Ventilators and Exhaust Heads, 601 High Street, Akron, Ohio. This article focuses on their static models made in 1921 (Fig 1). On a side note the company is still in business in the HVAC industry and still located in Akron, OH.

These reangle in size from 22″ diameter up to 110 inches in diameter. That gives a very nice range

Various Scales


Table 1

Table 1 shows the diameters in 1:24 range from 0.917″ to A quite massive 4.583″ …


Table 2

Table 2 shows the diameters in 1:48 range from 0.458″ to 2.292″ … that last one represents a ventilator some 110″/9.16 ‘ dia.


Table 3

Table 3 shows the diameters in 1:160 range from 0.138″ to 0.688″ …


Table 4

The Burt Ventilators as shown in Fig 1 were available in 15 sizes from the smallest 22″ dia ventilator (0.138″ in N scale) to the largest 110″ dia ventilator (4.583″ dia in 1:24).

I took the sizes for the 22″ and 110″ ventilator in each scale (3.49 mm and 17.46 mm for 1:160 scale for example) and put these numbers into an Excel spreadsheet (Table 4), sorting on the actual size (left two columns). This gave me 10 ventilators ranging from 3.49 mm to 116.42 mm. This gives me 5 or 6 ventilators for each scale from 22″ to 110″.

To the right is Evergreen tubing and rod dimensions. I can use the tubing for the 2nd-6th ventilators’ neck The smallest ventilator might make use of the No.212 rod.

Initial/Base Dimensions

I developed a .. very general cross-section from the illustration in Fig 1.

The important dimensions are A (Neck diameter) and B (Rim diameter) – from Table 3. With Sketchup I can dynamically scale a model by changing either A or B which will give the other dimensions.

One potential problem is Dim A … the ventilator neck diameter. If the ventilator is placed on a flat roof then no problem. If the ventilator is installed on a sloped roof then that neck needs to be longer – in “Real Life” this would have been a sheet metal pipe extending above the roof enough for the ventilator rim to clear the roof slope.

Solution 1 : print a neck on each ventilator that is long enough to clear any roof slope. This .. I don’t like since I don’t know what “any slope” might be.

Solution 2 : Match the neck diameter to Evergreen tubing/rod (or other product) to create a pipe for the ventilator to sit on. This would  allow the ventilator to fit any roof slope simply by adding longer rod/tubing. There is a difficulty with the smaller ventilators since the neck is smaller than the Evergreen tubing. I address that in the paragraph above.

Dimensions – V1

So from all the above I get this. The cells highlighted in gray show Evergreen tubing that I can use for the ventilator neck. This requires that there be a small stud on the bottom of the ventilator that will fit the ID of the tubing. The first row highlighted in red(ish) is using Evergreen 212 rod. This would require a socket in the base of the ventilator. Everything else .. depends on sourcing appropriate size tubing.

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