This sucks...

[jonofrey (John Onofrey, TREC#6546)]

…literally.

New construction. The first picture shows a duct box with jumper ducts joined to it from the upstairs bedrooms. This assembly does not join to the air handler, it just goes open to a grill in the hall which is a few feet away from the actual return air grill.

The second picture shows the jumper duct grill next to the return air grill in the upstairs hall.

So it’s a good thing that we are not pressurizing rooms because air is being pushed through the jumper duct system.

The bad news is that this seems to be a big heat exchanger. The temperature at the jumper duct grill was 90 degrees F. The return air grill measured normal at 70 degrees F.

I don’t understand why they didn’t just join the bedroom jumper air ducts to the plenum and pipe the return air directly into the system.

Not the first time I have seen this but seems like a design flaw to me. On the other hand, I guess it shouldn’t make any difference. Perhaps just an easier way to accomplish the same thing.

What is your opinion of this type of configuration?

[cbottger (Charley L. Bottger)]

If I am understanding properly you are describing the return from the upstairs bedrooms has to be drawn into the plenum in the attic then out into the hall through the back grill then into the front grill back to the furnace blower. I believe if you was to measure air from from the bedrooms you would find that you are moving little to no air from the bedrooms and you will have two different temps within the home. I think your term was the proper one it sucks.

[Gary_Reecher]

If I understand correctly there is a 20 degree temperature rise between the return grilles and at the air handler/furnace return? Something isn’t sealed or that flex duct has no insulation in it whatsoever. That is way too much temp rise between the grill and the unit. Something is wrong. They may have sized the a/c correctly using a manual J calculation but with that much additional load it will not keep up at design temperature.

[jonofrey (John Onofrey, TREC#6546)]

If I am understanding properly you are describing the return from the upstairs bedrooms has to be drawn into the plenum in the attic then out into the hall through the back grill then into the front grill back to the furnace blower. I believe if you was to measure air from from the bedrooms you would find that you are moving little to no air from the bedrooms and you will have two different temps within the home. I think your term was the proper one it sucks.

You understood correctly Charley, except the forward grill is the jumper duct grill and the rear grill is the return air to the system.

[kweiss (Kevin R. Weiss, TREC# 7108)]

I see these a lot in one particular neighborhood. You are definately right about the heat exchanger part. IR shows that in the summer it is well over 100 in the jumper duct. Air doesn’t move through the jumper unless the doors to the room are closed. Eventually in that case the temp comes down. I will be at one of these later this week, will see if I can get a good IR pic.

The bigger issue seems to be in the winter. When you get a convection air cycles going. The air in the jumper is cold from the attic, the warm air from the room rises and a nice little cycle develops. Homeowners consistantly complain about the “freezing cold hallway/wing/room.”

In the newer houses in this neighborhood, they cut costs further by just cutting a hole in the wall over the door of in the wall to allow return air when the door is closed. Which may actually be better since at least the heat exchanger part goes away.

[cbottger (Charley L. Bottger)]

You understood correctly Charley, except the forward grill is the jumper duct grill and the rear grill is the return air to the system.

I think if one was to have held a piece of newspaper over the grill in the bedroom you would have seen the paper fall to the floor.

[jonofrey (John Onofrey, TREC#6546)]

I think if one was to have held a piece of newspaper over the grill in the bedroom you would have seen the paper fall to the floor.

Agreed. I don’t understand why anyone would build it this way. It doesn’t seem to require any more materiasl to duct the return all from all bedrooms straight to the air handler.

[cbottger (Charley L. Bottger)]

Agreed. I don’t understand why anyone would build it this way. It doesn’t seem to require any more materiasl to duct the return all from all bedrooms straight to the air handler.

I have never in my 40 years observed a duct system like that but have been out of it for the last 6 other than in this business but just from past experience I would have doubts that system would be any other than a mess.