Environmental Issue & Sick Building Syndrome Blog

Most Common HVAC Errors, Mistakes and Issues that are Environmental Hazards

July 27th, 2013 10:40 PM by Dan Howard

Why does carbon monoxide only come back into the home some of the time?

Chimneys do not work as well when they are cold than when the weather is warmer. (That whole "warm air rises" and "chimneys are cold in winter" facts of physics) Also with the installation of higher efficiency furnaces that use fans to exhaust eh fumes in the furnace, these furnaces will draw fumes back from a hot water tank or clothes dryer into the home when the furnace is working   

Can my gas dryer or may gas “ventless” fireplace or space heater vent CO back into the home?

Your dryer can vent back into the home. A blocked vent with lint is one cause. As mentioned above, a furnace with a direct vent system can pull the fumes back into the home 

Aren’t I safe if I install a CO detector?

There is a delay built into residential CO detectors. The alarm may not go off until the CO has been at a dangerous level for hours or at an elevated state for months. I have twice seen a demonstration where a high quality Nighthawk CO detector was placed in an atmosphere of 100 PPM CO (toxic level) for an hour before the alarm went off.  The delay is designed to limit the number of times an alarm goes off due to background CO and CO from appliances like gas ranges.   

Where should a CO detector be installed?

Use a carbon monoxide detector with a digital readout and place it in the area likely to have the highest reading. That would be near a fireplace or hot water tank. To protect from heat exchanger openings, place the CO detector near a warm air register. 

What is an “orphan hot water tank”?

That term refers to a hot water tank that previously vented into a chimney with a furnace. If a direct vent (vent to the exterior side wall) furnace is installed, that furnace is not longer keeping the chimney warm enough to draw fumes up the chimney in cold weather.  That is an orphan hot water tank.

Why didn’t my heating person change the hot water tank vent when they installed a new furnace?

We don’t know without checking the conditions. The chimney may have been small enough to meet the requirements for proper venting. This is not very common, but possible. Another answer may simply be economics and convenience as well as the bidding process. The typical flue liner costs over $ 100.00, takes about an hour to install, and involves going to the very top of the existing larger chimney and installing the top of the liner and threading the flexible tube down the old chimney. Other methods such as installing direct vent systems may be more convenient, but have higher equipment costs. If a furnace installer includes the cost of changes, their bid will be higher, risking “losing the job.” For some that risk is more of a motivation than safety of clients.     

How do I know if I am having CO intermittent problems?                                                       

That is difficult to tell. Many professionals such as EnviroSpect have continuous CO monitoring equipment that logs the CO level across several days

Carbon Monoxide can be a Problem With Hot Water Tanks Too

Several  problems  can occur with hot water tanks occurs when a new high efficiency furnace is installed. When the new furnace that exhausts the fumes to the exterior using a venting fan, it can suck the carbon monoxide back down the chimney from the hot water tank into the air you breathe.

The Hot Water in the Home Smells Bad. What is the Problem?

When the hot water smalls like rotten eggs and the cold water does not small as bad, it is usually the result of organisms living in the hot water tank. Often this is Legionella which will survive up to 140.0 f, but can be other organic materials. The manufacturers offer replacement anodes that they will tell you “may” eliminate the problem, but often do not. Tank replacement is usually the answer. The bottom line is that turning your hot water tank to a low level for an extended time may be unhealthy for future residents and may create the need for tank replacement. 

Posted in:General
Posted by Dan Howard on July 27th, 2013 10:40 PM



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