JUCA Performance Chart

Customers are always impressed with how well their JUCAs produce heat. They sometimes ask us how to estimate how much their JUCA is really producing. Just use a normal thermometer to measure the warm air Outlet Temperature near the warm air outlet and then use the following chart to learn just how much heat the JUCA is actually sending out into the house.


.	Cool Return Air From House (65F) In living area or using cold air return				Cold Return Air From Basement (25F) WITHOUT a cold air return
Outlt Temp	Std 465cfm	Mid 1240cfm	Large 1460cfm	3/4 HP 2550cfm	Std 465cfm	Mid 1240cfm	Large 1460cfm	3/4 HP 2550cfm
70F	3 KBtu	5 KBtu	8 KBtu	14 KBtu	23 KBtu	45 KBtu	72 KBtu	126 KBtu
80F	8 KBtu	15 KBtu	24 KBtu	42 KBtu	28 KBtu	55 KBtu	88 KBtu	154 KBtu
90F	13 KBtu	25 KBtu	40 KBtu	70 KBtu	33 KBtu	65 KBtu	104 KBtu	182 KBtu
100F	18 KBtu	35 KBtu	56 KBtu	98 KBtu	38 KBtu	75 KBtu	120 KBtu	Not Recc
110F	23 KBtu	45 KBtu	72 KBtu	126 KBtu	43 KBtu	86 KBtu	137 KBtu	Not Recc
120F	28 KBtu	55 KBtu	88 KBtu	154 KBtu	48 KBtu	96 KBtu	153 KBtu	Not Recc
130F	33 KBtu	65 KBtu	104 KBtu	182 KBtu	53 KBtu	106 KBtu	169 KBtu	Not Recc
140F	38 KBtu	75 KBtu	120 KBtu	Not Recc	58 KBtu	116 KBtu	185 KBtu	Not Recc
150F	43 KBtu	86 KBtu	137 KBtu	Not Recc	64 KBtu	126 KBtu	Not Recc	Not Recc
160F	48 KBtu	96 KBtu	153 KBtu	Not Recc	69 KBtu	136 KBtu	Not Recc	Not Recc
170F	53 KBtu	106 KBtu	169 KBtu	Not Recc	74 KBtu	146 KBtu	Not Recc	Not Recc
180F	59 KBtu	116 KBtu	185 KBtu	Not Recc	79 KBtu	156 KBtu	Not Recc	Not Recc
190F	64 KBtu	126 KBtu	Not Recc	Not Recc	84 KBtu	166 KBtu	Not Recc	Not Recc
200F	69 KBtu	136 KBtu	Not Recc	Not Recc	90 KBtu	176 KBtu	Not Recc	Not Recc

. Example: a JUCA with a Large Blower is putting out warm air at an average temperature of 120°F. How much heat is it producing for the house?

In the table above, go down to the 120°F line. Then go across to the LARGE column(s). As long as the JUCA was drawing its blower air from the house (if it's in the living area) or from a cold air return, then it must be producing 88,000 Btu/hr for the house. If, instead, it had been installed in a basement or garage with the blower drawing cold air from that space, it would have to work MUCH harder to create the 120°F air, having to create about 153,000 Btu/hr. Think about this. In both cases, you would get the same effective heat in the house. But in the second case, the JUCA would have to work nearly twice as hard and burn nearly TWICE AS MUCH wood to accomplish the same heat! Much more intense fires would need to be used as well. In addition, the humidity in the house would also be messed up, because air that was upstairs that was already humidifed would have to be pushed out of the house through cracks to make room for the new warm but un-humidified air you were sending up there. This is why ALL central furnaces use cold air returns!

The physical explanation of this is that, in the second setup, you would necessarily be pushing previously heated warmed and humidified house air OUT through cracks to make room for the new air you're heating and bringing in. (The first method RE-CIRCULATED the warmed house air over and over, just adding a little more heat and humidity each time through the JUCA / furnace.)

There is another thing that can be learned fron this chart. It makes clear the value in using an optional blower when heating large areas. In our example above, (a rather large house in a cold climate), we needed about 88,000 Btu/hr to supply all the heat for the whole house. By using the LARGE blower, we had the air come out at about 120°F, a nice, safe, comfortable temperature. If, instead, we had just used the standard blower, (to create the SAME 88,000 Btu/hr for the house), you can see that the JUCA would have to be putting its air out at over 200°F (actually about 240°F), a VERY hot air temperature, which could even have safety implications. Again, the same amount of heat would be supplied to the house. But the very hot air from the smaller blower has some other consequences as well. The very hot air would immediately try to rise to the ceiling (remember High School Chemistry, where heat rises?) and it would move at relatively slow velocities. That means that it wouldn't be able to get as far out into the room before rising to the ceiling, so if you were sitting across the room, less heat would likely get to you to keep you cozy. In contrast, the larger blower's more moderate air temperature would allow the air to stay down where WE are longer, and the bigger air flow would distribute the heat more evenly over a large area, and even through ducts to the rest of the house.

Also note that the huge 3/4 HP blower would supply all that heat as air that would be under 100°F, resembling the air that Heat Pumps give out.

If you feel that your JUCA is not producing enough heat for the house, then there are three obvious things to check.

Make sure that your JUCA has a cold air return or otherwise has access to be able to draw house air into its blower.
Make sure that your ducting system is allowing the heat to get out of the JUCA. The easiest way to tell this is to check that the outer shell temperature of the JUCA is comfortable to touch. If it is hooked into a duct system, and the JUCA warm air chamber shell is warmer than 130°F, then that probably means that something in the duct system or connection is not allowing the warm air the JUCA is creating to get out and into the house ducts. Something in the ducts would need to be changed.
The other thing to check that REALLY affects output performance is the setting of the smoke pipe or chimney throat damper. If it is too open, the smoke from the fire could leave the JUCA too quickly for effective heat exchange to occur, which really can reduce heat output.

The JUCA Home Page is at: http://mb-soft.com/juca/index.html