HVAC Question - Return Air duct/vents requirement

Does a Duomatic Olson gas furnace require return air duct/vents? There is no central air installed in the house.

the furnace is approx 20 years old

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You haven’t provided enough information to answer properly, and they make a number of units. Basically, any forced air furnace needs “air” to flow in & out, in some configuration.
Try looking up the specs (using the model info) for install requirements provided by the manufacturer.

model number is HCS-90 Serial number 19595 HCGNU, I found the manual online but only talks about a cold air return for the ac unit and does’t specify if it does not have an ac unit connected.

Welcome back to our forum, Conrad Hershberger!..Enjoy! :smile:

It would seem that is a pretty standard FAU so , I would ask you, how do you expect the air to get where it belongs?
Unless I don’t’ understand what you’re asking…try posting a photo or two.

This is the only air intake, no return ducts.

Air distribution is like any other heating system, there are no cold air return ducts/vents installed the furnace intake is shown in the picture above. Since there is no ac unit installed and its not a high efficiency furnace, it does not need cold air returns. Am I incorrect in my thinking?

I would guess it depends on how tight the house/basement is built.

If I blow into a bottle, only so much air goes in then it stops going in.

A return air duct or rather the use of a duct is just a way to pull air from a remote location (if needed like a central hallway) back to the unit so it looks like in this case the room is acting as the duct. I’m guessing this is in an (open room) basement with distribution ducts and registers at remote locations? Now it could be that with the return at the unit it may interfere with the way the combustion/makeup air is being pulled into the unit (vortexes and such) but that is thinking out of the box. Just think of the gas heaters used in warehouses or shops where there is no ducting.

Larry Morrison - You are correct this is located in an open room basement, with distribution ducts going to each room of the house.


Yes this furnace and heating system require return air ducting.
Without it, like Larry said, its like blowing into a jar.
The return air ducting, properly sized allows for a balanced system.
Sometimes we find a central return but its located in the near center of the house and designed to allow air back to the furnace, from the heated space.

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ok thank you

The main issue is about air distribution throughout the house. The unit is in the basement. How does the air get from a bedroom (any room) back to the basement? Shut a door and the air stops.

Contrary to HVAC installers beliefs, Balancing the Return is more important than the supply. No duct, no balance.


As the responses above have mentioned, you need a way for air to get back to the furnace from the rooms above. However, a return air duct is not the only way to achieve this.
Did the door at the stairs to the basement have a solid surface or did it have louvers or some other way for air to flow through?

If you had a return air duct from the hall of the finished space to this furnace, this basement would be an unconditioned space. If air returns down the stairway to this basement, it is heated when the furnace is operational.

Below are a couple examples of doors that allow air to flow through.


That makes sense, it does have an open stairwell to the basement, however, there was a door way to the section the furnace was in. I can’t recall if that door had any louvers installed.

A good clue that there is a deficiency with the system is if a door between the unit and communicating space slams shut(or is difficult to close) when the blower is operating.

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