Common Return HVAC in Residential Home

[jar546]

Who out there requires calculations to show that there is adequate return from rooms with door (in the absence of pass through grills/ducts) on homes with a single common return?

Do you make sure that the doors are adequately cut to provide the minimum return air flow so that the rooms do not become positively pressured and inefficient?

 

[Keystone]

Do not run into this often but when we do we seek calcs as the cals in our opinion would need to be performed to initially size the system and ducting, frankly most supply houses do it for the contractor if they provide a blueprint.

2.2. The volume of supply air discharged back into the same space shall be approximately equal to the volume of return air taken from the space.

 

[Gregg Harris]

Who out there requires calculations to show that there is adequate return from rooms with door (in the absence of pass through grills/ducts) on homes with a single common return?Do you make sure that the doors are adequately cut to provide the minimum return air flow so that the rooms do not become positively pressured and inefficient?

Undercutting of doors is a poor choice and generally leads to inadiquate return, unless cut greater than two inches depending on the CFM that is supplied to the room.

 

[ICE]

Undercutting doors is the only thing that's ever done. Just enough to clear the carpet. I suppose more attention is given to this when new dwellings are built but 99.9% of furnace installs are replacements. I find the return air grills in hallways that are closed off with a door and it's been that way for sixty years. The fight I get about removing the door is amazing. I am told that undercutting all of the doors is an alternative to removing the door at the end of the hallway.

It is a poor arrangement but people aren't going to tear their houses up in order to fix this.

 

[jar546]

Undercutting of doors is a poor choice and generally leads to inadiquate return, unless cut greater than two inches depending on the CFM that is supplied to the room.

Yes, which is why I posted the questions. The lack of a response more than likely tells me that not many check for this during plan review or inspection.

 

[steveray]

I would say you are right Jeff....it's kinda like doing the math on windows and adjoining room for ventilation.....I don't think I have ever gotten a plan that would give me anywhere near that level of detail....I am lucky if I can get header sizes....

 

[fatboy]

I agree Jeff and steveray.............we don't look at it..........should we? Probably.....

Back in the UBC days, we did look at natural light and ventilation requirements.........then the IRC nixed the natural requirement.

 

[Frank]

We don't review single family HVAC Elect or Plumbing plans

 

[steveray]

We don't review single family HVAC Elect or Plumbing plans

I would...If we got them.....

 

[jar546]

We don't review single family HVAC Elect or Plumbing plans

I can see the electrical part because that is essentially a no brainer but not the mechanical? I don't agree with not looking at mechanical because of the requirements and how we often find problems with design and sizing. One of those things that gets swept under the rug due to lack of enforcement and or inspector knowledge

 

[mtlogcabin]

2.2. The volume of supply air discharged back into the same space shall be approximately equal to the volume of return air taken from the space.

That is not a requirement that is an exception for fuel burning appliances

5. A room or space containing a fuel-burning appliance where such room or space serves as the sole source of return air.

Exceptions:

1. The fuel-burning appliance is a direct-vent appliance or an appliance not requiring a vent in accordance with Section M1801.1 or Chapter 24.

2. The room or space complies with the following requirements:

2.1. The return air shall be taken from a room or space having a volume exceeding 1 cubic foot for each 10 Btu/h (9.6 L/W) of combined input rating of all fuel-burning appliances therein.

2.2. The volume of supply air discharged back into the same space shall be approximately equal to the volume of return air taken from the space.

2.3. Return-air inlets shall not be located within 10 feet (3048 mm) of a draft hood in the same room or space or the combustion chamber of any atmospheric-burner appliance in the same room or space.

There is nothing in the IRC that requires what the OP is asking.

 

[jar546]

First there is this part for residential:

M1401.3 Sizing. Heating and cooling equipment shall be sizedin accordance with ACCA Manual S based on building loadscalculated in accordance with ACCA Manual J or other

approved heating and cooling calculation methodologies.

Then there is this under the residential energy code:

N1103.6 Equipment sizing. Heating and cooling equipmentshall be sized as specified in Section M1401.3.

When you start getting into the ACCA Manuals, they are full of other information and requirements.

For those AHJ's that say, well I can approve other heating and cooling methodologies, what methodology are you approving?

So if you don't dig into Manual J, S and D, you really have no idea what you should be approving or inspecting.

Manual J finds the building load

Manual S sizes the system

Manual D covers the duct system, materials, friction loss, etc.

Then once you get into return air you have other info and requirements like this:

M1602.2 Prohibited sources. Outdoor and return air for aforced-air heating or cooling system shall not be taken from thefollowing locations:

​ 3. Aroom or space, the volume of which is less than 25 percentof the entire volume served by the system. Where

connected by a permanent opening having an area sized

in accordance with ACCA Manual D, adjoining rooms

or spaces shall be considered as a single room or space

for the purpose of determining the volume of the rooms

or spaces.

Exception: The minimum volume requirement shall

not apply where the amount of return air taken from a

room or space is less than or equal to the amount of

supply air delivered to the room or space.

 

[Francis Vineyard]

Not in the code but it sure would be nice to have filters for all return air grilles to help promote better efficiency instead of having to access the attic and crawl space. Did an inspection where the filter hadn't been attended to in 12 years since they lived there!

 

[Glenn]

For new home construction, we require Manual D, S and J, per the 2009 IRC. We review the HVAC designs. When a return is not provided in closed, habitable room, we apply the table from ACCA that provides how much undercut clearance is required for various size doors based on the CFM delivered to the room (Manual D, Appendix 1, Table A1-2, ). Often, after they see the redline table for undercuts (often very huge, for example, 200 cfm + 36" door = 2.7" undercut) we get a revised design with dispersed returns.

This is the path provided for in the IRC.

For equipment replacements, we inspect the equipment. We inspect existing portions of the venting and combusion air systems, but we do not inspect the air distribution system.

 

[jar546]

The reason that I posted this is because of the usual story we hear from contractors whenever they come into one of our municipalities and it sounds like this: "We just did 2 jobs in Abc town and they passed it."

Not much infuriates me more so I am going to go on a rant using this as a subject.

WARNING, I will be very opinionated, harsh and direct. Unfortunately, since I am the administrator for this forum I will be viewed as a bully which I don't like, which is one of the reasons I try not to post stuff like this.

First and foremost, I would like to know why plan reviewers and inspectors simply choose not to enforce minimum requirements. Is it because?:

1) They don't know what they are doing themselves. (they don't know what they don't know)

2) They don't have any adopted codes to go by and therefore wing it.

3) There are adopted amendments to the code that exclude those requirements.

4) They are lazy.

5) They feel it is OK to be arbitrary on code officiating based on what mood they are in.

6) They don't think it's important.

7) All of the contractors are so professional, accurate and code knowledgable that they often wonder why they even have a job since there is no reason to do review or inspections.

I really can't think of any other excuse or reason and more than likely it's an excuse and not a reason.

These residential systems are pretty simple for the most part. Air goes in, air comes back, air goes back out again. Houses like mine also take advantage of outside, fresh air. If you can't balance the system then it will never function properly, it will strain the blower motor causing an increase in the electrical bill and cause the system to run more often since it is out of balance and inefficient.

What a disservice to the community and homeowners to take a stance of inadequate, lazy, ineffective code enforcement. For what reason I ask you?

I lived in a 10 year old house with a common return which did not have jumper ducts or transfer grills and did not have adequate undercutting of the doors. This was my direct experience:

1) My electric bill was high

2) We had to leave the doors open almost all of the way to keep them from being sucked shut whenever the system came on

3) If we closed the doors for privacy, the bedrooms were hot or cold depending on time of year while other parts of the house were at the correct temperature

4) The cycle time was longer when the system was on

I now live in a house that has jumper ducts in the attic from ceiling to ceiling and:

1) My electric bill is much lower

2) I never have to leave doors open in order for the system to work properly

3) The temperature is very consistent due to the correct balancing of the system

4) The cycle time is less, hence resulting in #1

IF you have adopted the I-Codes then you have a legal obligation to ensure that construction meets a minimum standard. In this case, the mechanical and energy section of the IRC fully covers forced air systems.

So what is your excuse?

 

[Darren Emery]

First and foremost, I would like to know why plan reviewers and inspectors simply choose not to enforce minimum requirements. Is it because?:

1) They don't know what they are doing themselves. (they don't know what they don't know)

2) They don't have any adopted codes to go by and therefore wing it.

3) There are adopted amendments to the code that exclude those requirements.

4) They are lazy.

5) They feel it is OK to be arbitrary on code officiating based on what mood they are in.

6) They don't think it's important.

7) All of the contractors are so professional, accurate and code knowledgable that they often wonder why they even have a job since there is no reason to do review or inspections.

I really can't think of any other excuse or reason and more than likely it's an excuse and not a reason.

So what is your excuse?

Jar - I agree with your entire statement. You did, however, miss two reasons that I can think of for not inspecting/enforcing certain items:

8) Staffing levels not sufficient to inspect EVERY item governed by the codes - therefore choices regarding what to inspect must be made.

9) Lack of political backing to enforce items which will result in the supervisor's/city manager's/city council member's phone to ring

There are likely others, but these two came to mind almost immediately, for some reason....

 

[Mr. Inspector]

10) Get fired because the boss of my 3rd party company thinks I am nickpicking and gets too many complaints.

 

[jar546]

Jar - I agree with your entire statement. You did, however, miss two reasons that I can think of for not inspecting/enforcing certain items:8) Staffing levels not sufficient to inspect EVERY item governed by the codes - therefore choices regarding what to inspect must be made.

9) Lack of political backing to enforce items which will result in the supervisor's/city manager's/city council member's phone to ring

There are likely others, but these two came to mind almost immediately, for some reason....

10) Get fired because the boss of my 3rd party company thinks I am nickpicking and gets too many complaints.

I own a third party agency and have the following response to the above:

8) that is pretty sad and I would like to know who is responsible for determining what is let go from a legal standpoint.

9) I really don't give a **** about number 9 because I never cared in the past

We get complaints all of the time but as long as it is in black and white and part of the code we stand by our people.

I have personally lost contracts and business with municipalities because we enforce the code fairly and equally to everyone, even in today's political climate of political intimidation. I stand by our decisions and don't care if I lose business because I refuse to compromise my ethics and values due to inappropriate intimidation. I encourage everyone to stand by their guns and hold their positions. Am I making less money? Yes. Does it hurt to lose jobs? Yes. Is it stressful l to be politically intimidated? Yes. Do I care and will I sell out to those who are corrupt? No. Do I sleep at night a lot better knowing I did my job to the best of my ability with no compromise? Yes.

The only barriers we have in front of those are the ones that we allow to be there. Don't let others affect your ethical performance and direction.

 

[mtlogcabin]

(24) The building official may waive minor building code violations that do not constitute an imminent threat to property or to the health, safety, or welfare of any person.

I am old school when the priority of the codes focused on health and safety. So I prioritize the inspections and plan review based on life safety in accordance with staff levels. We do not require plans for plumbing, mechanical or electrical on IRC structures.

 

[Darren Emery]

I am old school when the priority of the codes focused on health and safety. So I prioritize the inspections and plan review based on life safety in accordance with staff levels. We do not require plans for plumbing, mechanical or electrical on IRC structures.

Same here. The BO decides how to prioritize inspections. At this point, we only require floor plan, site plan, and elevations for IRC structures.

 

[Keystone]

mtlogcabin - thanks for pointing out the incorrect application of the code section I jumped the gun and should've read thru the section.

I know there is a section the IMC and or IECC under commercial aplications pertaining to supply/return air being equal.

 

[jar546]

Same here. The BO decides how to prioritize inspections. At this point, we only require floor plan, site plan, and elevations for IRC structures.

And down goes your ISO rating and up goes the insurance.

 

[steveray]

And down goes your ISO rating and up goes the insurance.

We use mainly 10 year old codes which is set by the state......We don't even try to get a good ISO....

 

[mtlogcabin]

I have been doing private insurance inspections for over 8 years now for many different insurance companies and none have ever asked for the ISO rating of a building department on their reports. Fire department ISO's are required on about 70.% of them

I dropped from a 3 to a 4 because the state never went to the 2009 IRC because of sprinklers and no Wildland-Urban Interface code adopted.

The BCEGS program assigns each municipality a BCEGS grade of 1 (exemplary commitment to building code enforcement) to 10. ISO develops advisory rating credits that apply to ranges of BCEGS classifications (1-3, 4-7, 8-9, 10). ISO gives insurers BCEGS classifications, BCEGS advisory credits, and related underwriting information.

Basically there are only 4 different rating groups and they only apply to the homes that where constructed during the time period the rating group was assigned

http://www.isomitigation.com/bcegs/0000/bcegs0004.html#q5