Main Distribution Duct Heat Outlet

Main Duct on the back of a B-3B Virtually all JUCAs include a large warm air outlet, so that you could send enough warm air to other parts of the house to entirely heat it all! Free-Standing (B-3 series) JUCAs have this outlet on the back, near the top, as shown in the picture (where it could be hidden by suitable "privacy screens" on both sides. Built-In JUCA Fireplaces (F-9A series) have the outlet on one or the other side of the body (opposite the side where the blower is connected).

Most larger JUCAs use an 8" by 16" opening. This is directly compatible to commonly available "Main Distribution Ducting", so no custom sheet metal work should be necessary. It is large enough to be able to carry enough warm air to supply the many rooms of your whole house, if you choose to heat it all with the JUCA.

We have always been bemused by competing "add-on furnaces" which only have a single 8" or 10" diameter warm air outlet, and which claim to be able to heat a whole house. Whether their units are capable of CREATING enough heat to do this is another matter. But if such heat is created, and available, it is necessary to have sufficient airflow (CFMs) to distribute the heat everywhere you want.

Have you ever noticed how LARGE the big rectangular main duct is from your conventional furnace (usually along the ceiling in a basememt)? That's to carry all that air. If all that air had to squeeze down to pass through an 8" diameter hole, the amount of air that would get by would be far less.

We sometimes use the example of a fireman's 3" hose. It carries a LOT of water. Imagine that they are fighting a fire on your neighbor's house and they need just a little more hose. So, you graciously give them a five-foot long piece of your garden hose, to extend their hose. How much water would you expect to come out the end of their 3" hose and nozzle? Not much, because even that short section of the much smaller garden hose limited the flow of water. Same deal in air ducting, if there is even a single flow restriction, like having to pass through an 8" diameter outlet. THAT'S why JUCAs have much bigger outlet duct connections, comparable to the existing ducts in your house!

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By the way, this argument also helps clarify why JUCA strongly suggests using one of the five optional blowers (rather than the standard 465 CFM one) when feeding the warm air throughout the house. The number of CFM (cubic feet per minute) needs to be roughly proportional to the house area being heated. The larger the house area, the more CFM needed, and therefore the larger the blower (or, being Politically Correct, the Air Handler), and the larger AREA ducting needed.

If we again think about that fire hose analogy, what if their truck's pump broke down and you loaned them your basement sump pump to supply the water for their 3" hose? Even though the hose could carry many gallons per minute, the pump couldn't supply that much, and the water would sort of dribble out. Same thing with the large house ducts and a moderate sized blower.

Back of a B-3B, showing the main duct outlet at top We don't want to get into the ugly mathematics of the technical aspects here (a Technical presentation describes all that). Suffice it to say that JUCAs are designed and intended to heat entire houses!

It is not actually necessary to use this capability. Some people get a JUCA (with a Standard or Mid Blower) to just supply heat for the room the JUCA is in. NO PROBLEM! Just block off the Heat Duct opening with a Main Distribution Duct End Cap (About $5 at any heating/plumbing store). Then, if someday, something silly happens again in the Mid-East (and it will), where conventional heating fuel sources are interrupted, the JUCA's blower could be up-graded and the ducting provision used then, to heat the whole house!

The top photo above shows the upper back of a free-standing JUCA where the lip provided allows a connection to galvanized ducting (8" x 16" here). The second photo shows the entire back of a B-3B to show where the Heat Outlet Duct Connection and the Blower are located on a free-standing JUCA.

F unit showing duct connection stub on the right This arrangement allows you a LOT of flexibility!

We'll look at a built-in F-9A model here, but most of the ideas also apply to all the free-standing models as well.

To begin with, see that this unit has it blower on the LEFT, and the main distribution duct connector stub on the right, around halfway up that sidewall.

(The chimney connector is that thing on the top!)

F unit showing ducts-a First, with the NORMAL duct connector location, you could use a standard available fitting, (A SHORT 90 DEGREE ELBOW) to send the warm air UP. This would allow connection into a duct system which is overhead.

Often, when JUCAs are installed in a basement recreation room (F-9A or B-3B) or in an unfinished basement (B-3A), this is a logical approach.

F unit showing ducts-b Or, again with the NORMAL location, you could use a standard fitting, (A SHORT 90 DEGREE ELBOW) to send the warm air DOWN. This is a common arrangement for installations where a JUCA (F-9A, B-3B or B-3D) is in an upstairs living room.

Often, in such situations, the warm air ducts are along the basement ceiling, below the JUCA. This duct would pass through the floor, to feed ducts which are below the room that the JUCA is in.

F unit showing ducts-c Then there are some possibilities when ALL of the surrounding materials are entirely masonry (no wood, not even hidden wood!). This situation would allow the JUCA body to be installed in a much more compact space. For example, sometimes cinder blocks are used to build the walls surrounding a JUCA F-9A.

In this special situation, the normally required safety clearance around the body of the unit is not necessary. (For the examples mentioned above, the surrounding clearance space had to be there any way, so the ducts and their elbows had little effect on increasing the necessary installation space). With a cinder block wall surrounding the body of the F-9A, that clearance space is not necessary, so that cinder block wall could be virtually right against the body of the unit.

Since the duct still needs to be connected, it could pass THROUGH that cinder block wall. The duct could then elbow up, down, or wherever. If the installer is REALLY good at planning, he might be able to have the duct outlet line up with ONE missing (8" by 16") cinder block! (But from experience, that's hard to do!

F unit showing ducts-c Continuing our consideration of situations where NO wood is anywhere nearby and the unit is surrounded by ALL MASONRY materials, like brick, stone, or cinder blocks:

For specific installations, it is possible to request that the duct connection be on the TOP of the warm air plenum. Again, this is ONLY when the surrounding wall materials are ALL MASONRY.

This installation actually has a slight disadvantage over the NORMAL duct stub location. When you first start a fire, the blower is still off. It will only turn on once the JUCAs temperature sensor probe recognizes that the air has gotten warm enough to distribute to the house. With our NORMAL location, what happens is that warm air initially accumulates in the upper chambers of the JUCA heat exchanger system (warm air rises). Since the probe is generally installed in this chamber, it is quickly aware that heat is available, and the blower turns on pretty quickly.

If the warm air outlet is on the very top of that chamber, then much of that early heat doesn't accumulate there but rather goes right up into the ducts. There's nothing really wrong with that, but the blower is often delayed in knowing to turn on.

F unit showing ducts-e Continuing our consideration of situations where NO wood is anywhere nearby and the unit is surrounded by ALL MASONRY materials, like brick, stone, or cinder blocks:

For specific installations, it is possible to request that the duct connection be on the BOTTOM of the warm air plenum. Again, this is ONLY when the surrounding wall materials are ALL MASONRY.

This type of installation has no trouble letting heat accumulate in the upper portions of the heat exchange chambers (like the example just above did). But there is often a different matter to consider.

Often, people request this specific configuration when a JUCA F-9A is to be embedded into a massive chimney structure, similar to how traditional fireplaces were made. Because of this circumstance, the JUCA body will never again be accessible. No problem there.

However, remember that temperature probe that turns the blower on and off? It's best location is in the upper portions of the heat exchanger chamber. This generally allows three possibilities:

Finally, regarding this last configuration, our drawing is generally slightly incorrect! The bottom surface of that side warm air chamber is only around 4" wide. In order to attach an 8" wide duct to it, it is nearly always necessary for us to "flare out" the side wall of the JUCA, about 5" to make that surface large enough to install the duct connector. This somewhat defeats the purpose of really making the whole works compact! Also, installers have found it pretty involved to be trying to attach a duct in that location because there's very little room to work! For these reasons, we tend to suggest using the normal side location of the duct stub. Installers have a FAR easier time in doing the duct connection!

We normally use an 8" by 16" rectangular stub connector so that standard sized, locally available main distribution ducting can be used. Every imaginable elbow and fitting already exists as a standard item, so no custom fabrication of ducting should be necessary. On the F-9A, it is normally located about halfway up the side of the unit, centered (front to back), and with the long dimension horizontal. All this is subject to adjustment for specific applications. Sometimes, it is more convenient for the installer if we move it forward or back, up or down, or rotate its orientation. Sometimes a different sized main duct is desirable, either larger or smaller. Let's talk!

By the way, the same multitude of choices is available regarding the blower connection when the blower is REMOTELY LOCATED.

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