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Hi all - 8 years ago I finished my basement. The heat pump heating unit/AC is gas heat. Next to it is my gas water heater. It was in what is basically was a hallway. We walled this off, but I put 12x18inch vents in the drywall high and low leading to the space where the HVAC/WH is. On the other end of that hall is a 12x12 room (unfinished). The room is open to this unfinished hall where the HVAC/WH is. There is a door leading to this room from my finished area, and I put a 2x2 foot vent in the bottom of it.

I vented it as such because there was concern about combustion/CO2/etc. I wanted air to be able to get to the HVAC/WH. The finished area outside this in my basement is about 1500 square feet or so. There is no venting to the outside. When doing this project 8 years ago, someone suggested maybe I run a breather vent of sorts to the HVAC area.

The HVAC/WH vent into what seems to be 4-6inch diameter tin double-wall that merges and heads out a stack in my roof.

I have had no issues in 8 years. I keep a Co2 detector nearby the HVAC. Never went off.

Now I want to finish that 12x12 room. I would basically be adding a door which would close off the HVAC/WH hall. I could put vents high/low in this door if needed. While the room would now be drywalled, etc., everything else is the same.

My question is whether this would somehow reduce airflow to the HVAC hall and choke it off, or cause other problems/CO2 issues, etc. While I've had zero problems in 8 years, I'm concerns that maybe there is just enough air getting to these devices, and added a door (although vented) could tip the scales.

Thanks in advance for your thoughts...
 

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There are rules stating how much ventilation you need and when it's required.

Depends on the btu input of the equipment in the room.



I don't think finishing the room will make a difference.
 

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There is a lot to consider when installing provisions for combustion air. Most building codes are available for free viewing online. If your area has a code based in the International Residential Code, look it up. In NY, it is in Chapter 24 Section G2407, Combustion, Ventilation and Dilution Air. You can work through it with your specs and know it is safe.
 
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The gas you mean is CO, not CO2. CO is carbon monoxide, CO2 is carbon dioxide.
If your CO detector is UL listed it’s not for anything beyond an all out catastrophic event. It will not alarm unless CO levels get above 70 PPM for an hour or more. So you could have CO at a continuous 69 PPM and the alarm will never sound.
By contrast, most fire departments will not enter a structure without breathing apparatus if the CO is above ~20 PPM.
Low level non-UL listed CO detectors are what you want for monitoring.
 

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Hammered Thumb
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Can't picture the whole "hallway" situation, but in addition to the fuel gas venting reqm'ts Thomas directed you to IRC G2407 that you can follow along, don't forget about requirements for accessible space around the appliances and getting them in and out as well.
 

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retired framer
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All the houses here have air duct form out side to near the floor at the furnace .

Your next furnace will be HE so I would run the 2 PVC pipes for that now and let them supply air as needed.
 

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All the houses here have air duct form out side to near the floor at the furnace .

Your next furnace will be HE so I would run the 2 PVC pipes for that now and let them supply air as needed.
Only in certain areas is there a requirement to have combustion air from outside.

The intake duct or vent is not required in mine.

Few houses are tight enough to actually need the intake; the ones that are usually have direct vent furnace and power vent water heater in the first place. (the power vent uses indoor air for combustion but won't backdraft due to using a strong fan)

Mid efficiency furnaces are also still available in the states.
 

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retired framer
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Only in certain areas is there a requirement to have combustion air from outside.

The intake duct or vent is not required in mine.

Few houses are tight enough to actually need the intake; the ones that are usually have direct vent furnace and power vent water heater in the first place. (the power vent uses indoor air for combustion but won't backdraft due to using a strong fan)

Mid efficiency furnaces are also still available in the states.
So when your house needs air, you count on having a draft somewhere.

A closed furnace room is always warm in the winter, I can't think of a better place to have a cold draft. :biggrin2:
I still think if you are going to finish a basement I would put the pipes in for the next furnace. How much would that save when needed.
 

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Some power vent furnaces burning indoor air can be adapted to use outdoor air. The real problem is having a power vent indoor air burning furnace near a gravity vent hood water heater. The furnace can draw combustion air from the water heater vent. Even with seemingly enough air, I would be concerned.
 

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All I can tell you is that it's not a requirement in most cases to have the open intake to outside and units aren't starved for combustion air.

It may be a requirement in your area.

You said that all houses have the intake which is wrong.

There just needs to be vents to the rest of the basement.

The leakage is sufficient to supply enough combustion air, basement is under slightly negative air pressure. An appliance taking air from inside makes the basement slightly more negative, drawing in a little more air.

It's not optimal and personally, i prefer direct vent.

It's only necessary to put plastic pipes before hand if finishing will impact the ability to do so later.
 
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