Thread: HVAC/water heater combustion air

I purchased a new home and in my basement is the utility room. It has the water heater and the furnace in there. To vent the room with fresh air they have installed a 6-8 inch round duct to the outside. The duct outside is only 5 inches from the graded ground. All summer I have been getting dirt and debris getting sucked into it and into my utility room. This doesn't seem right. I am also worried that when it snows it will completely cover the vent and not allow sufficient airflow.

Is there some code that should dictate this vent to be higher off the ground to account for debris and snow?

Here is an image: It is the white vent under the window on the right.


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Hello Andrew
Yes there are certain requirements for ventilation of an enclosed room with gas fired equipment....and your concern about the vent being covered during the winter with snow is a valid concern.

Typically, a minimum standard for venting and ventilation is to have two vents each of 100 sq. inches to provide both high and low vents into the room. In your picture there is only one vent opening - the white square plastic vent. I'm not from the snow country, but that looks too low, and inadequately sized. I dont have all the answers - I dont have all the information - size of room, size of heating equipment or whether there are other considerations. Voice your concerns to the builder, and let him know that you are going to contact a local HVAC (Heating, ventilating, air conditioning contractor) to get an independent assessment of the situation.

I also see another gadget - a metal vent - is that for a piece of equipment like a decorative gas fireplace in that ground level room?

Andrew,since it is a new home,contact the local building department,to ensure every thing is up to code.

Originally Posted by Andrew James

I purchased a new home and in my basement is the utility room. It has the water heater and the furnace in there. To vent the room with fresh air they have installed a 6-8 inch round duct to the outside. The duct outside is only 5 inches from the graded ground. All summer I have been getting dirt and debris getting sucked into it and into my utility room. This doesn't seem right. I am also worried that when it snows it will completely cover the vent and not allow sufficient airflow.

Is there some code that should dictate this vent to be higher off the ground to account for debris and snow?

Here is an image: It is the white vent under the window on the right.

Each appliance should have a manufacturer's ventilation requirement on a booklet included with each. Add these requirements and you should have the minimum requirement for the combustible air supply.

Read G2407.6.2 from the International Residential Code for a rough idea of the one opening method for combustion air. Also, read 2407.10 & 2407.11

Originally Posted by Chris Weekly

I also see another gadget - a metal vent - is that for a piece of equipment like a decorative gas fireplace in that ground level room?

Yes that is for a gas fireplace directly on the other side of that metal vent far right. Is there something wrong with that too? haha


Here are some more images:


As you can see from the first and second image that we have fresh air coming in from the above vent. To the left of the HVAC unit is the water heater. The room isn't walled in yet. Also notice the debris from outside on the ground.

Originally Posted by Harry Janssen

Andrew,since it is a new home,contact the local building department,to ensure every thing is up to code.

The City office is closed today so I will call them on Monday and see what they can tell me. Thanks for the suggestion.

Measure the actual size of the pipe. There is a big difference in volume between a 5 or a 6" pipe.
Normally that pipe would seem adequate, but there appears to be a lot of suction to draw that much debris. You are right to question it. Closing in the room and adding a door is going to increase the negative pressure.

Be prepared to have the drywall opened up so that the builder can install a larger vent pipe or two higher up the wall. The grill over the inlet reduces the air supply, BTW.

The vent measures 7.5 inches. The tubing says 8 x 5 on it so I would guess it is 8 inch tubing. My furnace is a 60,000 btu unit.

[QUOTE=Andrew James;212195]Yes that is for a gas fireplace directly on the other side of that metal vent far right. Is there something wrong with that too? haha


No, but it looked like a direct vent setup that might have a bearing on the equipment down below (like a direct vent water heater). I was just ruling out that from being a factor.

Since the heater is a high efficiency condensing type furnace that will also have an impact on the venting/ventilation requirements. The distance from grade is still a factor that looks to need correction.

What type venting is the water heater?

Up here just north of Montana we have a mandatory exterior-supplied combustion air requirement, but then we seal up our houses really well, and in the winter and probably don't open windows (could be for almost six months of the year). There is also a requirement for fresh air duct supply directly into the return air system. Both of these are insulated 6" flexible ducts (with a plastic VP over the insulation). They are fitted with dryer style hood vents with screens but no flappers. If neither water heater and furnace require room air for combustion then the HVAC guy only has to worrry about the make-up air requirements of thebig kitchen range hood.

What has this got to do with you? - That intake looks wrong, both in height and type/style. The duct should be insulated inside the home if the exterior air being drawn in is sufficient to cause condensation on the duct. There really shouldn't be that much air moving into the house in the summer that you are sucking in noticeably quantities of dirt, unless you've got some serioius exhaust vents (bathroom, laundry, kitchen), or some sort of stack effect drawing air out of the upper parts of your house.

The water heater has an exhaust out the top which goes through a pipe that leads through the house and out the roof.

As far as exhaust vents in the house, we only have fans in the bathrooms which we rarely use. And the clothes dryer I suppose.

I haven't chatted with the city yet. (I have been on a business trip)

Anyway, what happens if indeed the city sees this and says it is not right?

Originally Posted by Andrew James

I haven't chatted with the city yet. (I have been on a business trip)

Anyway, what happens if indeed the city sees this and says it is not right?

What happens may be that local AHJ will likely require that the corrections need to be made by a qualified professional - an HVAC or other qualified contractor.
Who pays for corrections? YOU, the homeowner may have to get a lawyer to help the builder see it your way. It seems the builder should make good on proper installation and corrections as necessary..... Getting a lawyer involved may be more expensive than just getting your own independent contractor. Sometimes it's costly being right.

I just spoke to the city code inspector on the phone and I described to him the issue with the combustion air vent. He told me it was a code violation but not to worry about it. He has seen people with pillows placed in the vent with no problems.

Should I accept this answer? What kinds of dangers could be present if the vent gets blocked up?

What was the building inspector smoking,when he said some people block the vent with a pillow,a vent should never be blocked no matter what
Many appliances will not operate at all if the vent is blocked

I agree with you Harry but what are the REAL concerns? Is it just that my furnace won't run at 90% efficiency or is it more like my family won't have air to breath when in the basement?

Andrew,the real issue,carbon monoxide,a real deadly concern.

Simply, if the duct is within 5" of the grade its too low.

Put an extender on the outside portion it to bring it up to 18" minimum above grade with an elbow on the extension to prevent water entry and screen.

To stop air being pulled in you can extend the interior portion of the pipe to within several inches of the floor and place a bucket under the open portion. The bucket will act as a cold air trap. And air will be drawn in when needed.

Combustion air: how to provide adequate combustion air for combustion appliances in newer tighter buildings and in older homes that have been made more airtight - Solar Age Magazine

Andrew;

Without ample combustion air the fireboxes and venting systems will over heat cause a possible fire, but surly will cause premature failure, called burnout of the appliance, be extra concerned, if one or both units are power vented as the lack of free combustion air will cause the reverse flow of exhausted carbon monoxide and dangerous odorless gas to re enter the area through the unused appliance. This inspector has the duty to protect the life and safety of others, with your duty is to report this under qualified person before he approves something to cause a death.