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Can a single return suffice for AC in a two-story house?

rcdawson | Posted in Mechanicals on

The house in question is a 1400 Square foot, two story house with forced air heating. It has a single return on the first floor and also has a very large duct to the outside on the return side. Fortunately for heating costs, the house is located in southern California where it generally doesn’t get too cold.

It does get hot in the summer, however, so am considering central air conditioning. It is a relatively simple matter to add additional return ducting to the first floor. (The heater, and thus the central air, will be located below the first floor.) Putting a return on the second floor would be extremely difficult.

The single return on the first floor seems to work acceptably, although certainly it would clearly be better to have returns in each room. My question: how much would the proposed air conditioning be compromised by not having any return on the second floor? I recognize the hot air rises (or conversly cold air sinks); will cold air sinking leave me with a refrigerated first floor and a still too hot second floor. Can I compensate by redcing the flow to the first floor? Is the proposed installation, with just a return from the first floor, worth a try?

Is there any air flow modelling software that might be useful for analyzing this?

Richard

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Richard,
    There is no simple answer to your question. A well-designed forced air distribution system (as I'm sure you know) needs to have return ducts from every room with a door. Your house doesn't have that. (Here is a link to an article with more information on return ducting: Return-Air Problems.)

    There are many comfort problems arising from attempts to use a forced-air distribution system for a single-zone system in a two-story house -- especially if the same ducts are used for both heating and cooling. Here is a link to an article with more information: Keeping Cool in a Two-Story House. (In addition to reading the article, I suggest that you also read the comments on that page.)

    One possible solution to your dilemma is to install a ductless minisplit upstairs to provide cooling.

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