Return Ducts

[nrichards]

As a general rule of thumb, should'nt there be a return vent on each level of the home? Did a 2-story condo, 1600 SF. Place only had one return on 2nd floor ceiling.

[Charley L. Bottger]

Originally Posted by nrichards

As a general rule of thumb, should'nt there be a return vent on each level of the home? Did a 2-story condo, 1600 SF. Place only had one return on 2nd floor ceiling.

There are no rules of thumbs in HVAC only SQ inches. A well balanced system depending on the construction design would normally have a return up and one down but no defined rule stating that it must have two.

[David A. Andersen]

Where do you live?
First of all, you cannot effectively condition the air of a two-story building with one HVAC system unless it has a zoning system. Seeing that it is a condominium (rather small structure) and only requires one HVAC unit for the cubic feet within the building space, and a zoning system cost as much as a second HVAC system you often get one unit per condominium. They seem to always go one step further and only put a return at one floor or the other.
If you live somewhere where you have a heating and cooling season, then the duct design will only function properly in one season or the other.
A return air on the second-floor ceiling will remove the heat that rises in the summertime (good). However, in the wintertime (with the same system) when you must remove the cold air to be treated, you must have a return at the floor on the first floor. There is no way that you can remove the cold air from the first floor with a return on the second-floor ceiling. It is also impossible to remove hot air from the ceiling of the second floor when it's located on the floor of the first floor.
Remember this one concept, the HVAC system is a "sucker" not a "blower". It sucks the air out, since the equipment to be treated and puts it back where it came from.
Installer spent a lot of time with the supply system and totally ignore the return. In actuality, the return is more important than the supply. If the return is not properly done it will also destroy your compressor.
This information is for your use only.
I highly recommend that you do not try to take on the HVAC and general contractor industry with a limited knowledge because they will argue with you to the end.
I don't know how many hours I have spent in the last 12 years arguing with these people. However I no longer have to do that with a thermal imaging camera. I snap a picture and you can see the air stratification in the building. No more arguing!

[Brian E. Kelly]

Originally Posted by dandersen

Where do you live?
First of all, you cannot effectively condition the air of a two-story building with one HVAC system unless it has a zoning system. Seeing that it is a condominium (rather small structure) and only requires one HVAC unit for the cubic feet within the building space, and a zoning system cost as much as a second HVAC system you often get one unit per condominium. They seem to always go one step further and only put a return at one floor or the other.
If you live somewhere where you have a heating and cooling season, then the duct design will only function properly in one season or the other.
A return air on the second-floor ceiling will remove the heat that rises in the summertime (good). However, in the wintertime (with the same system) when you must remove the cold air to be treated, you must have a return at the floor on the first floor. There is no way that you can remove the cold air from the first floor with a return on the second-floor ceiling. It is also impossible to remove hot air from the ceiling of the second floor when it's located on the floor of the first floor.
Remember this one concept, the HVAC system is a "sucker" not a "blower". It sucks the air out, since the equipment to be treated and puts it back where it came from.
Installer spent a lot of time with the supply system and totally ignore the return. In actuality, the return is more important than the supply. If the return is not properly done it will also destroy your compressor.
This information is for your use only.
I highly recommend that you do not try to take on the HVAC and general contractor industry with a limited knowledge because they will argue with you to the end.
I don't know how many hours I have spent in the last 12 years arguing with these people. However I no longer have to do that with a thermal imaging camera. I snap a picture and you can see the air stratification in the building. No more arguing!

Hey David, if you don't mind, share one of the those stratification pictures. I would be very interested to see one.

[John Allingham]

See (11) below. Check the code in your area.

6.2.4.7. Return-Air System

(1)

The return-air system shall be designed to handle the entire air supply.

(2)

Except as provided in Sentences (3) and (4), return ducts shall be constructed of material having a surface flamespread

rating

of not more than 150.

(3)

Where any part of a return duct will be exposed to radiation from the furnace heat exchanger or other radiating part

within the

furnace, such part of a return duct directly above or within 600 mm of the outside furnace casing shall be

noncombustible

.

(4)

Return ducts serving solid fuel-fired furnaces shall be constructed of noncombustible material.

(5)

Combustible return ducts shall be lined with noncombustible material below floor registers, at the bottom of vertical

ducts and under

furnaces having a bottom return.

(6)

Spaces between studs and joists used as return ducts shall be separated from the unused portions of such spaces by

tight-fitting metal stops or wood blocking.

(7)

A vertical return duct shall have openings to return air on not more than 1 floor.

(

A public corridor shall comply with Sentences 6.2.3.9.(4) and (5).

(9)

The return-air system shall be designed so that the negative pressure from the circulating fan cannot affect the furnace

combustion air supply nor draw combustion products from joints or openings in the

furnace or flue pipe.

(10)

Return-air from a dwelling unit shall not be recirculated to any other dwelling unit.

54

(11)

Except for floor levels that are less than 900 mm above or below an adjacent floor level that is provided with a returnair
inlet, at least one return-air inlet shall be provided in each floor level in a dwelling unit.

[David A. Andersen]

Sorry Brian, I forgot about you...

Just for info; the first is from a BCAM and the second is from a BX320.

[Brian E. Kelly]

Originally Posted by dandersen

Sorry Brian, I forgot about you...

Just for info; the first is from a BCAM and the second is from a BX320.

Cool pictures

[David P. Valley]

I had a house yesterday, where the returns were installed on all the outside walls and the supplies were installed at the inside walls.

I want what that installer was smoking.....