Thread: Small room and 115,000 btu's

At yesterdays afternoons inspection I had one of those Red Flag moments. I entered the mechanical room in a new Fox Ridge home and was surprised to find a 75,000 btu furnace and a 40,000 btu water heater (both gas). The room was a mere 5'x6', but it had louvered bi-fold doors that opened to the laundry room! This is what the superintendent on site was so proud of!

So we have a 7x5 laundry room with a louvered door and off of the laundry room we have the mechanical room for the second floor.

I did some quick onsite calculations and discovered that the mechanical room was about half the size it needed to be, without an external makeup combustion air being provided. The super was watching me do the calculations and realized what I was trying to explain to him, but his kept on saying that it was approved by the city and they had their CO on the home. I then brought in the fact that the dryer in the laundry room would be sucking the air out of the room about as fast as it would be entering through the louvered doors! Again the CO came into the conversation.

I finally just told my client that they did not need to buy the home unless the mechanical room had the proper makeup air increased for the room and a solid door and threshold was installed for the mechanical room to separate it from the laundry room.

I figure my phone should be ringing in about an hour or two!

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Scott,

It is much worse than half the required size, it is probably 1/20 the size needed.

That louvered door is not going to cut it, first, the louvers are to high above the floor, the louvered area in a wood louvered door is quited limited in net free vent area, and there is not high opening.

Take a 30" wide door, 6" on each side for the jamb and hings stile, that only leaves 18" width by 80" less probably 14" at the bottom and less another 6" at the top for about 80" less 20" or 60" high, making the louvered opening only 18" x 60" = 1080 sq inches x .25 net free air for wood louvers = 270 square inches - that isn't much.

Originally Posted by Jerry Peck

Scott,

It is much worse than half the required size, it is probably 1/20 the size needed.

That louvered door is not going to cut it, first, the louvers are to high above the floor, the louvered area in a wood louvered door is quited limited in net free vent area, and there is not high opening.

Take a 30" wide door, 6" on each side for the jamb and hings stile, that only leaves 18" width by 80" less probably 14" at the bottom and less another 6" at the top for about 80" less 20" or 60" high, making the louvered opening only 18" x 60" = 1080 sq inches x .25 net free air for wood louvers = 270 square inches - that isn't much.

Agreed, the builder said he could just remove the bifold doors and that would then make the room large enough!

FYI, if anyone is looking at a Fox Ridge home you need to be on the lookout for this. This is one of their standard floor plans that they started to produce in 2008

Even if the vented/louvered doors were high and low enough, would they satisfy "two permanent openings" per 2006 IRC?

Scott,

Are those poly lines next to the draft hood on the WH?

rick

Originally Posted by John Arnold

Even if the vented/louvered doors were high and low enough, would they satisfy "two permanent openings" per 2006 IRC?

John,

The would be as "permanent" as two holes cut through the wall would be.

The door "could" be replaced with a non-louvered door.

The two holes cut through the wall "could" be patched and filled, heck, those two holes through the wall "could" even have a small piece of cardboard taped over them.

Now, with the door, what would happen "if" the home owner hung clothes on a hook on the door?

Probably about the same thing if that home owner hung clothes on a hook above the upper hole and placed a laundry basket in front of the lower hole.

In those aspects, *neither* would be of any good.

I can imagine a home owner with two holes (openings) through the attic noticing all the hot or cold air one day and saying 'No wonder it takes so much to heat/cool this place, I can stop that hot/cold air ... ' and they go into the attic and place cardboard or wood over the tops of those holes, thinking 'Why on earth would someone put two holes through the ceiling is beyond me.'

Then the family starts getting headaches and dizzy over time, but, hey, they sure solved that problem, whoever was stupid enough to put those holes there in the first place ...

Maybe the designer calculated the area using the fan assisted calculation or they used a combination of the combustion air and ventilation system.

There is more than one way to achieve the requirements for combustion air.

Also you can't go by on what the homeowner may do later. They may knock out a wall to give enough space. You have to go with what is there at the time not what could be in the future!

Originally Posted by Rick Hurst

Scott,

Are those poly lines next to the draft hood on the WH?

rick

Or proper support and strapping for the B vent, or ...

Originally Posted by Wayne Carlisle

Maybe the designer calculated the area using the fan assisted calculation...

Wayne, What's the "fan assisted calculation"?

Section 304.5.2 of the IFGC

I tried to copy and paste but it really gives some weird stuff. However if you have the 2006 IFGC you can find it there.

Originally Posted by Wayne Carlisle

Section 304.5.2 of the IFGC

I tried to copy and paste but it really gives some weird stuff. However if you have the 2006 IFGC you can find it there.

Thanks. I see it now in the 2006 IRC, G2407.5.2

Also in the 2006 IRC. (underlining and red text are mine)
- G2407.5.2 (304.5.2) Known air-infiltration-rate method.Where the air infiltration rate of a structure is known, the minimum required volume shall be determined as follows:
- - For appliances other than fan assisted, calculate volume using Equation 24-1.

(formula given)

- For fan-assisted appliances, calculate volume using

Equation 24-2.

(formula given)

- For purposes of this calculation, an infiltration rate greater than 0.60 ACH shall not be used in Equations 24-1 and 24-2.

However, that is only for when the air infiltration rate is known and is known to be 0.60 ACH or less.

And how do you know it isn't known?

And i know you will come back with "How do you know that it is?"

That's why I said the designer may have used different methods to achieve compliance.

First you need to start at G2407.5 (304.5):

From the 2006 IRC.
- G2407.5 (304.5) Indoor combustion air. The required volume of indoor air shall be determined in accordance with Section G2407.5.1 or G2407.5.2, except that where the air infiltration rate is known to be less than 0.40 air changes per hour (ACH), Section G2407.5.2 shall be used. The total required volume shall be the sum of the required volume calculated for all appliances located within the space. Rooms communicating directly with the space in which the appliances are installed through openings not furnished with doors, and through combustion air openings sized and located in accordance with Section G2407.5.3, are considered to be part of the required volume.
- - G2407.5.1 (304.5.1) Standard method.The minimum required volume shall be 50 cubic feet per 1,000 Btu/h (4.8 m3/kW).
- - G2407.5.2 (304.5.2) Known air-infiltration-rate method. Where the air infiltration rate of a structure is known, the minimum required volume shall be determined as follows:
- - - For appliances other than fan assisted, calculate volume using Equation 24-1.
- - - - (Equation 24-1)
- - - For fan-assisted appliances, calculate volume using Equation 24-2.
- - - - (Equation 24-2)
- - - ACH = Air change per hour (percent of volume of space exchanged per hour, expressed as a decimal).
- - - For purposes of this calculation, an infiltration rate greater than 0.60 ACH shall not be used in Equations 24-1 and 24-2.

I believe what it will come down to is how you define "known".

"Designers" (that is the term you used, and appropriately so) use "design" numbers, not "known" numbers. "Known" numbers are only arrived at after testing of as-built systems.

A "designer" "designs" based on known "design standards", with known and unknown variables in the field based on field conditions, construction methods, quality and workmanship of construction, and properly applied (or lack thereof) sealants, weather stripping, tapes, air barriers, etc., as only a small portion of the known unknowns.

Hmmm

I'm thinking of measurements, senarios, two gas fired appliances, dryer sitting off to the right sucking air through the hall louver (which is a full louver door) where there is more than enough air, which allows air to the mechanical room for the WH and HVAC unit (not to mention the dryer is not running 24 7) . Technically the room for the WH and HVAC is plenty big enough with plenty of air flow. If it is deemed to not be quite enough air this is a pretty sinple fix.

Clothes hung on the door. Basket put in front of the door. Vents into an attic where someone is going to go up there and block off.

Just some observations. Just some observations. The builder does need to address the slight air flow concern but when convinced of how simple a fix it is I am sure he will go along with it.

This appears to be a second floor with an attic above. The builder does not have to address it he has to address it to the the HVAC company. I am sure if the figures were reasonable enough and the thought behind it was more than I am right and you are wrong I do not see the HVAC company having a problem with the minor fix for the air flow.

Originally Posted by Rick Hurst

Scott,

Are those poly lines next to the draft hood on the WH?

rick

Nope, they are PEX lines.

3 phone calls and counting. One from the builder, one from the builders HVAC contractor and one from the real estate agent. Folks are just having a hard time understanding that it could be wrong because the city gave them a CO!

Don't forget that in all of those calculations we have a laundry room with a dryer that will be sucking air out of the room like a little tornado!

The solution so far is a High/Low venting system with the air coming from the ventilated attic. One slight problem is that the attic space above this room is about a foot high due to the slope of the roof, going to be a tight working space! Oh well, I only report it!

As for the size of the room it would need to be right at 700 square feet or a room around 25'x30' with no dryer to use the natural room air for the makeup combustion air. From what I have discovered while doing a little research, with the dryer the room would need to be right at 35'x45' with an 8' ceiling. This is assuming that this is a basic residental electric dryer. You don't even want to know about a gas dryer, I would have to take my shoes off to count on my toes!

Originally Posted by Ted Menelly

Hmmm

I'm thinking of measurements, scenarios, two gas fired appliances, dryer sitting off to the right sucking air through the hall louver (which is a full louver door) where there is more than enough air, which allows air to the mechanical room for the WH and HVAC unit (not to mention the dryer is not running 24 7) . Technically the room for the WH and HVAC is plenty big enough with plenty of air flow.

"plenty of air"???

Let's see, the code states that the room needs to have a minimum required volume of 50 cu ft per 1,000 Btu/hr, which means that for the two gas-fired appliances in that room of 75,000 Btu/hr and 40,000 Btu/hr for a total of 115,000 Btu/hr / 1,000 Btu/hr = 115 x 50 cu ft = 5,750 cu ft to be sufficient code minimum volume without having to provide combustion air.

The room was, Scott said, 5 ft x 6 ft x (making a presuming here) 8 ft high, or, 5 x 6 x 8 = 240 cu ft of volume in that room.

I'm not sure about you, but, to me, 240 cu ft of space provided does not magically equal, or even come close to, the required 5,750 cu ft of volume necessary to not require combustion air.

If it is deemed to not be quite enough air this is a pretty sinple fix.

"if ... not quite enough"????

Not even close.

"this is a pretty simple fix"

Yeah, provide proper minimum combustion air.

G2407.5.3.1 (304.5.3.1) Combining spaces on the
same story.

Each opening shall have a minimum free
area of 1 square inch per 1,000 Btu/h (2,200mm2/kW) of
the total input rating of all appliances in the space, but not
less than 100 square inches (0.06 m2). One opening shall
commence within 12 inches (305 mm) of the top and one
opening shall commence within 12 inches (305 mm) of
the bottom of the enclosure. The minimum dimension of

air openings shall be not less than 3 inches (76 mm).

Okay, there are 115,000 Btu/hr for ALL appliances in that space, which requires 1 square inch free vent area per 1,000 Btu/hr, or, 115,000 Btu/hr / 1,000 Btu/hr = 115 or 115 square inches of free vent area per opening.

Okay, you say, I'll put in a nice standard 12" x 12" opening as that is 144 sq inches and throw a nice white metal grille on it to make it look better ... Whoa!, with that metal grille on there, that 12" x 12" opening is now only 100.8 sq inches due to the reduction of the vent area by the metal grille itself, and you need to have 115 sq inches, not 100.8 sq inches.

Okay, you can go with a 12" x 14" opening and grille and end up with 117.5 sq inches per opening.

No problem, by the way, the top opening needs to start within 12" of the ceiling and the bottom opening needs to start within 12" of the floor ...

This appears to be a second floor with an attic above. The builder does not have to address it he has to address it to the the HVAC company.

Close on that one.

The builder DOES have to address it. If his HVAC company does not THE BUILDER still needs to. No matter how you look at it, THE BUILDER *is the responsible party*.

However, as Scott says, once you open that up to the open space with the clothes dryer, one needs to be aware of, concerned about, and address the clothes dryer sucking air OUT of that space WHILE RUNNING ... those calculations are not based on "best case scenarios", those are based on "worst case scenarios". If that clothes dryer is like ours, it will be running half a day on a weekend and maybe some during the week evenings. Do you want spillage during those times?

Ted, your response seem real callous and lackadaisical to me, trying to justify something as being okay when it was far from being okay, even going to the extent of saying to the effect of 'Hey, the clothes dryer does not run more than several hours, it's okay to have spillage under those conditions at those times for however long those conditions exist.

Originally Posted by Jerry Peck

"plenty of air"???

Let's see, the code states that the room needs to have a minimum required volume of 50 cu ft per 1,000 Btu/hr, which means that for the two gas-fired appliances in that room of 75,000 Btu/hr and 40,000 Btu/hr for a total of 115,000 Btu/hr / 1,000 Btu/hr = 115 x 50 cu ft = 5,750 cu ft to be sufficient code minimum volume without having to provide combustion air.

The room was, Scott said, 5 ft x 6 ft x (making a presuming here) 8 ft high, or, 5 x 6 x 8 = 240 cu ft of volume in that room.

I'm not sure about you, but, to me, 240 cu ft of space provided does not magically equal, or even come close to, the required 5,750 cu ft of volume necessary to not require combustion air.



"if ... not quite enough"????

Not even close.

"this is a pretty simple fix"

Yeah, provide proper minimum combustion air.

G2407.5.3.1 (304.5.3.1) Combining spaces on the
same story. Each opening shall have a minimum free
area of 1 square inch per 1,000 Btu/h (2,200mm2/kW) of
the total input rating of all appliances in the space, but not

less than 100 square inches (0.06 m

2). One opening shall

commence within 12 inches (305 mm) of the top and one
opening shall commence within 12 inches (305 mm) of
the bottom of the enclosure. The minimum dimension of

air openings shall be not less than 3 inches (76 mm).

Okay, there are 115,000 Btu/hr for ALL appliances in that space, which requires 1 square inch free vent area per 1,000 Btu/hr, or, 115,000 Btu/hr / 1,000 Btu/hr = 115 or 115 square inches of free vent area per opening.

Okay, you say, I'll put in a nice standard 12" x 12" opening as that is 144 sq inches and throw a nice white metal grille on it to make it look better ... Whoa!, with that metal grille on there, that 12" x 12" opening is now only 100.8 sq inches due to the reduction of the vent area by the metal grille itself, and you need to have 115 sq inches, not 100.8 sq inches.

Okay, you can go with a 12" x 14" opening and grille and end up with 117.5 sq inches per opening.

No problem, by the way, the top opening needs to start within 12" of the ceiling and the bottom opening needs to start within 12" of the floor ...



Close on that one.

The builder DOES have to address it. If his HVAC company does not THE BUILDER still needs to. No matter how you look at it, THE BUILDER *is the responsible party*.

However, as Scott says, once you open that up to the open space with the clothes dryer, one needs to be aware of, concerned about, and address the clothes dryer sucking air OUT of that space WHILE RUNNING ... those calculations are not based on "best case scenarios", those are based on "worst case scenarios". If that clothes dryer is like ours, it will be running half a day on a weekend and maybe some during the week evenings. Do you want spillage during those times?

Ted, your response seem real callous and lackadaisical to me, trying to justify something as being okay when it was far from being okay, even going to the extent of saying to the effect of 'Hey, the clothes dryer does not run more than several hours, it's okay to have spillage under those conditions at those times for however long those conditions exist.

All I was saying is this is an easy fix. Fix the air flow and there is no need to even tralk about room size. With the size of the room out of the picture then the air flow is a no brainer. It appears that is was addressed as both to the biulder. Builders do not want to hear that you can do this because the rooms are to small and you need much more air flow in those rooms and it doesn't matter if the city gave a CO

Again. Way to much is being made of this situation. We know that no one is going to increase the size of the rooms so it never should have been brought up because it is an air volume problem.

Basically with out saying it they were all called dumb shits and they need to make a bunch of corrections.

There is only one correction that needs to be addressed.

Sometimes it is much better to

"keep it simple stupid"

And Scott

You turned to your client and said they did not need to be buying the home and the discussion or fix has not even been fianlized. Way to much of the attack mode going on here.

There are twice as many toes on my right foot where I have had disputes with builders about fixes needed. They may question but that is as far as it goes.

Therre is only one problem with Scotts senario. That is air volume and nothing else and that is a seriously easy fix.


Well unless he found other concderns in those 2 rooms.

Originally Posted by Ted Menelly

And Scott

You turned to your client and said they did not need to be buying the home and the discussion or fix has not even been fianlized. Way to much of the attack mode going on here.

No, not really an attack mode. I'm very soft spoken, but when a timid young first time buyer is being bullied by a builder and an agent, the Daddy in me comes out. Could be why I do not get that many agent referrals?

There are twice as many toes on my right foot where I have had disputes with builders about fixes needed. They may question but that is as far as it goes.

OK, I don't understand that analogy but I will go along with it... I think...

Therre is only one problem with Scotts senario. That is air volume and nothing else and that is a seriously easy fix.

Well unless he found other concderns in those 2 rooms.
[/LEFT]

Yes, air volume is the main culprit. The other would be adding a solid door and threshold to make the room independent of the laundry room.

Another issue is that this builder builds in 16 states and is using this same floor plan in those states.

Originally Posted by Scott Patterson

Yes, air volume is the main culprit. The other would be adding a solid door and threshold to make the room independent of the laundry room.

Scott,

If they do that solid door thing and the combustion air to the attic, they will need to remove the furnace and water heater so they can remove the drywall, install insulation in that room, then install, finish and paint new drywall, then reinstall the appliances as that will allow quite cold air into that room and destroy the energy calculations and the basis for everything they did energy-wise.

Of course, being as that room will now get to freezing and below at times, all those pipes and that water heater will need protection from freezing too.

Oh, wait, that PEX close to that draft hood and B vent should stay warm enough ... until it is moved away where it is allowed to be ...

The louvered opening into the mechanical room would be sufficiently large to provide makeup air to the furnace and water heater, if not connected to the laundry room with another louvered door. I don't think there's much of an argument against that statement.
Unfortunately, the louvered door from the laundry room into the hallway space does not have sufficient area to provide makeup air to the furnace, water heater, and dryer that will be installed.
This IS a simple fix. Change the door into the hallway, using a door with a KNOWN free area, that will allow the required free area to provide makeup air for all three appliances.