Encapsulated crawl space

[DH_homeowner]

I am thinking of encapsulating my crawl space in the Atlanta area to reduce moisture and mold issues. I currently have a 80% gas furnace in the crawl space as well as a gas tank water heater. I am wondering if there will be enough combustible air to run these appliances after the space is encapsulated. The basement waterproofing contractors I have talked with said the crawl space will not be airtight after encapsulating, but they will seal off the foundation vents. Do I need to put in a new 90% or greater direct vent furnace before encapsulating?

[sktn77a]

You will need an external air supply for your existing furnace if you are sealing the crawlspace. Check the furnace manufacturer's installation instructions and get an HVAC company to confirm and do the necessary work. You shouldn't need to replace the furnace because of this.

[chuck78]

yes, code requires a lot more combustion air than just a little infiltration. not a good idea to totally seal off all major sources of outside air for combustion purposes.

How about you leave one or two open depending on size, and put a dehumidifier down there to REALLY reduce the moisture problem the right way? Cheaper than a new furnace and water heater, but then again, the efficiency of the 92% equipment will pay off in several years. Your crawl space will still be less humid with a dehumidifier.

[Shophound]

Even if you went with a 90% furnace, the water heater would still require combustion air.

Ask your contractor if your existing furnace and water heater can be provided with dedicated combustion air sources.

[micdundee]

for a true insulated/sealed crawl space at least a 90, sealed combustion and a tankless outside wh. seal all wire & pipe penetrations add one supply with motorized damp. to the rate of ,i believe 2 cfm/50 cubic feet of space. most will run dehumidifiers for a few weeks before final ground seal is completed. i don't know the desired rh needed. your contractor will.