This post, concerning heating system issues, is my fourth in the series of crawlspace inspections … and we’re in the middle of our crawlspace evaluation, with some more bad things on our way.

1. Cracked foundation / possible structural problems
2. Leaking foundation
3. Drainage problems / flooding crawlspace
4. Plumbing components issues – leaking water supply lines, drain pipes, crawlspace water heater installation problems
5. Heating system issues
6. Electrical components issues
7. Floor framing and structure support issues
8. Structural pest infestation – those are Termites, Powder Post Beetle, Carpenter Ants
9. Mold problems
10. Crawlspace ventilation and insulation

5. Heating system issues – if your crawlspace is subject to excessive moisture presence or flooding, every component / appliance installed in this area will deteriorate much faster than in a dry environment. A heat exchanger, which is one of the gas forced air furnace’s main components, is vulnerable to moisture, and excessive corrosion will compromise it over time; ex. it might cause it to crack, develop holes, block its interior or cover burners with rust flakes, which could create hazardous conditions.

Therefore, if you have an older furnace located in the crawlspace (I would consider 10-15 years as being older in moist conditions), have it checked on a seasonal basis by a licensed HVAC contractor. Ask them to evaluate your heat exchanger for integrity, and make sure that you always have a functional Carbon Monoxide detector installed in your house. When selling your property, have a written statement from the heating contractor confirming your furnace condition.

Metal air ducts of the furnace installed in the crawlspace also corrodes, sometimes severely, developing holes, and occasionally separating. Critical areas are:

Directly under the furnace, where the galvanized steel often corrodes due to a leaking air conditioning coil drip pan
Under the leaking humidifier
On duct connections

Try to locate moisture / leakage sources and check corroded areas for soft spots or holes. If there is a hole, it should be fixed, and the air duct section replaced or sealed properly. This is done for two reasons:

1. (holes and gaps on air return ducts) To prevent crawlspace air from being sucked into the air ducts and distributed through the house – if there’s moisture or mold – all that contaminated air will be infiltrating your living space.

2. (holes and gaps on air supply ducts) For dry and underground crawlspaces (you might also have a slightly elevated house structure and crawlspace / foundation walls exposed / above the ground, which will be explained in the Ventilation / Insulation chapter of Crawlspace Inspection series) there will be no impact from any open air supply ducts, except for wasting your money spend on heating. However, in poorly ventilated / saturated with moisture areas, additional heat creates a perfect mold growing environment. What’s even worse? With poor ventilation and air pressure building up in the crawlspace area, the air has to escape somewhere, and often travels into the attic of the house (through the plumbing walls, chimney pipe chase, wall cavities). In the attic, without proper ventilation, it will cause more mold and create further damage.

Other items to check for on your crawlspace installed furnace (some of them also apply to / are identical for the water heater):

Stable support under the furnace (shouldn’t be placed directly on the ground) or it might be suspended under the floor with proper mounting hardware and required clearances

  • Proper clearances around the vent pipe – at least 6” from any combustible materials for a single wall pipe and 1” for a double wall pipe
  • Proper slope of the furnace vent pipe – it has to rise continuously from the furnace to the chimney entrance at a minimum of ¼” per foot (except for the high efficiency furnaces)
  • Vent pipe secured properly – at the furnace, chimney, and along its run
  • The furnace gas supply connector must be heavy wall pipe – no dryer / kitchen range type flexible connectors are permitted in Illinois for furnace connections
  • Electrical furnace power supplying coduit must be properly secured

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