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Return air question


rlskfoster
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I recently inspected a double wide and I had a question about the way the HVAC return air was set up.

The HVAC unit sits in a 8 x 8 room along with the Water Heater and the Electrical panel. Total Electric.

HVAC is right on the floor and feeds to floor ducts throughout the house. My question is abou the return. The top of the unit is open except for the the filter. Is there any rules or regulations about return set-ups. I couldn't find anything and I was hoping one of you A/C guru's might know if this is okay.

By the way everything seemed to heat and cool okay.

Buster

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This is standard configuration for mobile homes. Production costs are what 'mobile' homes are all about. Making an opening on top (or on the bottom) of the unit is the easiest, fastest way to provide a return - no ductwork! The only challenge is that if the occupants close the door to that room, then the unit is being starved of return air. Sometimes there is a vent cut in that door to allow air flow, or sometimes the door is cut WAY high from the floor to allow air return underneath.

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Originally posted by Steven Hockstein

Since the system is totally electric, the open return is not an issue. When the system uses gas, propane, or oil as a heating fuel this is a dangerous condition if the open return results in negative pressure in the utility area and pulls fumes from the chimney (and into the living area).

It may not be a safety issue, but it certainly is an issue. Without an adequate return air path, the thing won't work properly.

The utility room has to have at least one very large opening in the wall or door. Or the door can be undercut -- at about the level of your knees.

If the room is tight, there'll be no appreciable flow through the ducts and the coils will likely overheat. With luck, it'll short cycle on high limit. Without luck, it'll burn itself out.

- Jim Katen, Oregon

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Hi,

I have to agree with Jim. Think of the thing as a big blow dryer. Ever covered one end of a blow dryer? Unless it is getting enough air to keep it cool, it will shut itself down until it cools off. Electric furnaces have the same thing, an over-temperature limit switch that will cause them to short-cycle when they aren't getting good airflow.

Almost without exception, when I open up the access panel on electric furnaces installed in small close rooms or closets in manufactured homes around here I find that there are melted wires and signs of overheating. Sometimes they have plenty of makeup air, but the filters are so clogged that they can't get enough air and overheat anyway.

OT - OF!!!

M.

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The entry into this room is a cased opening. It is wider than a normal 3.0 door so someone would probably have to work at it to make a door work.

That all makes sense and it hadn't even occured to me at the time to kinda of look at the room and its opening as the return.

Thanks for the responses.

Buster

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Originally posted by Jim Katen

Originally posted by Steven Hockstein

Since the system is totally electric, the open return is not an issue. When the system uses gas, propane, or oil as a heating fuel this is a dangerous condition if the open return results in negative pressure in the utility area and pulls fumes from the chimney (and into the living area).

It may not be a safety issue, but it certainly is an issue. Without an adequate return air path, the thing won't work properly.

The utility room has to have at least one very large opening in the wall or door. Or the door can be undercut -- at about the level of your knees.

If the room is tight, there'll be no appreciable flow through the ducts and the coils will likely overheat. With luck, it'll short cycle on high limit. Without luck, it'll burn itself out.

- Jim Katen, Oregon

Jim,

You are absolutely right. I should have been more clear. You need air to be able to flow back into the room for the air to circulate through the building.

I was focusing on a situation where there is an open return close to the furnace and causes fumes to be pulled down the flue. This can happen even if there is an open return in a room with return ventilation provided. Many residential HVAC contractors estimate the air flow through the system and never really calculate the actually CFM requirements.

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