IN FEBRUARY 2023, I described the sanctuary’s HVAC system in this post. Just recently, I have revised three aspects of my earlier understanding. The newer picture looks like this:
Below the jump, this post describes and documents the salient results of what I learned from my recent explorations.…
Supply air
Originally, the heating and ventilation system seems to have employed all four overhead registers to supply treated air to the sanctuary. Three of them are visible in this photo from Dedication Day (1948).
Then in 2017, installation of a smaller heating system cannibalized the massive rigid side ducts in order to place round flexible ducting inside them, which connects from the rooftop penthouse only to the smaller, more central registers.
Below is view from the attic above the Bimah, showing a rectangular hole cut in the old rigid duct, and a smaller, newer duct inside it.
The above information thus modifies what I stated in February 2023, namely that the two central upper grilles above the Bimah were originally return grilles. Rather, the same horizontal rigid duct spanned all four overhead registers.
Return air
Vent alongside the Bimah
The only original return ducting that I know of that’s extant is located off of the Bimah’s south wall. It is still an active part of the HVAC system. As I noted previously, its grille is largely hidden by one of the overstuffed red chairs. Below is a view with the chairs moved out of the way.
The opening is 30″x18″. And the images below, taken from the other side of that wall, show the rectangular duct for that register, as it comes down from the attic.
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| Looking upward |
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| Looking downward |
The next images show the (dusty) bottom inside of that duct, which is 3″ below the carpeted Bimah floor. This return duct thus does not seem to connect to anything beneath the Bimah.
(I remain a bit puzzled as to the overall original system configuration. The sum total of the cross-sections of the original supply ducting seems larger than that of the only original return duct, yet I would expect them to be the same in a properly designed system.)
Vents near floor
Below is the vent grille at the foot of the south-side Bimah steps. In 2023, I assumed incorrectly that this grille (and its counterpart on the north side) indicated the presence of a return duct for the HVAC system.
There is also a similar vent in each of the exit corridors (normally hidden behind the corridor doors, which are kept propped open), making a total of 4 such vents. However, it turns out that they have nothing to do with the HVAC system!
Below is what I saw after removing the grille on the north side of the sanctuary’s east wall. The opening simply vents the space underneath the Bimah.
For example, below is what I saw after removing the grille in the south corridor, and then peeked inside. The views shown here are representative of the other openings, as well.
I’m not sure that this can be called a crawlspace, because I could not find an obvious way for a person to get in.
Flying termites, on the other hand, did have a ready way in through the grilles. That’s according to our termite inspector, who happened to be on site the same day that I removed the grilles. He found frass just inside a couple of the openings, so he treated those spots. Happily, before replacing the grilles, Ruben taped fiberglass window-screen fabric to the back of each one, to keep termites from getting in (or out!) in the future.
(The screws are merely fastened to the plaster wall—which means that if the grilles are opened again, a molly will probably be needed to hold each screw in place in the future.)
One interesting detail inside was the metal anchor plate that is highlighted in the image below. It holds a short post located maybe 3′ back from the front of the Bimah, near the centerline of the sanctuary space. To me, it is a sign of a significant structural member.
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