Two Letters Re: “Cross-wire” Your Home Heating and Save Money

Mr. Rawles,
First, let me extend my heartfelt sympathy to you and your family on the passing of your wife. As a Christian, I am confident she is in a good place and free of her suffering, though sorely missed by the rest of us.

I have been a heating/ air-conditioning / refrigeration technician for the last 30 years. I own and use combustion analyzers to maximize performance of my customer’s appliances and both minimize the carbon monoxide (CO) they produce but also take a snap-shot of the ambient CO level in the building. I feel it is important to point out that while CO detectors are worthwhile (or at least a little better than nothing), they are not infallible! Far too many of them are improperly installed near kitchens, water heaters, furnaces and other combustion appliances! Nearly ALL fuel burning appliances produce CO at some point of their operating cycle. If a good, sensitive detector is placed too close to that appliance, it will “FALSE” on that short period emission of CO. False alarms desensitize the residents to the alarm, a very bad thing indeed. The solution to this problem by the Underwriter’s Laboratories (at fire department requests) has been to create a testing standard that is targeted to preventing FALSE alarms rather than insisting the device alarm when needed. I have seen this demonstrated, repeatedly, by placing a detector in a zip lock bag then filling the bag with 100 PPM CO calibrating gas. After an hour, none of the UL approved detectors did anything!! Scary, to say the least. IMHO they are unreliable as a result.

An AC powered detector will not work during power interruptions – a time when alternate, untested heat sources are likely to be in use! A battery powered device should always be present if any alternate heat sources not using utility power are used.

CO detectors have a finite life span, on the shelf or installed in the home. They can be “poisoned” by exposure to certain chemical fumes or very high levels of CO. Once poisoned, they will never respond to CO – at any level. My suggestion is to properly install a CO detector near all sleeping areas as high on the wall as possible. However, in addition to installing a detector, do not depend on it as they are, IMHO, unreliable. Far too many times I have measured high levels of CO in homes so equipped where no alarm ever sounded. In others, I have repaired serious heating plant problems where the alarm had sounded but the fire department condemned the detector rather than finding the problem !

Like most risks, proper understanding of the problem can be most helpful. In the case of CO, at least some things to consider are;

1. All un-vented heaters are extremely high risk. Oxygen depletion sensors do not address the problem AT ALL.

2. Cook stoves, particularly ovens, put out large amounts of CO and the standards consider it acceptable! Heed the warnings NOT to use them for space heating!

3. Space heating appliances that burn gas, oil, coal or wood can, and often do, produce high, unacceptable levels of CO in the flue gas. This can ONLY be measured and corrected by a properly trained professional – spend the money to protect yourself by hiring a well qualified technician to service your appliance(s). If he does not have a modern combustion analyzer, FIRE HIM !! Either get a printout of the readings or try to observe them on his instrument.

Note that LP gas is the most common fuel used (but certainly not the only fuel) where people are overcome by CO due to several factors including the higher carbon content of the fuel and it’s tendency to be difficult to burn cleanly. Gas can truly produce odorless CO! The most common warning I have seen is high indoor humidity. Fuel oil and solid fuels are, IMHO, the least likely to cause problems as a blocked flue or defective appliance will produce enough smoke and odor to warn of CO risk. In many cases, soot on the walls is a pointer to serious problems.

A lot of detective work can be required to find / correct CO problems. Sick appliance(s), exhaust fans, clothes dryers, inadequate combustion air, defective chimneys, improper installation, missing blower doors are just a few of the possible issues. With all due respect to firefighters, a CO problem often is not something that can be found during a short visit !! It requires a thorough knowledge of the systems involved and, quite often, a lot of time. It has been my experience that, in my area, the vast majority of systems are improperly installed or maintained.

Here is a link that echoes much of what I have written.

My combustion analyzers are less expensive than his (all four of them) but my results remain consistent and also prove the finite life span of the expensive detectors I use. Mine are sensitive enough to often tell if there is an active tobacco smoker in the house!!

Please use my comments in any way you feel will benefit your most useful blog!

Sincerely, – Mike G

Hello Jim,
It’s been a long time since we’ve corresponded, and I’m glad to see you’re still around and active. I was also saddened at the loss of your wife, and hope you and your family are otherwise healthy and prosperous.

I wanted to give folks a second option on intermixing their common combustion heating systems (e.g., Propane, Natural Gas, Fuel Oil), with the less common one (e.g., Wood, Pellets, Corn, etc). In order to do this, one must first understand how a conventional furnace functions. It is actually two independent systems, with an emergency interlock. The first system simply ignites a burner when the thermostat requests heat. That generally involves a series of steps, such as forced draft fans, pilot lights, electric spark, etc.; but the primary function is to safely light the main burner. Once the main burner is burring, the heat being produced heats up the air in the furnace plenum. The plenum is the large metal box to which all of the ductwork attaches. The plenum has three temperature sensors (usually simply b-metal switches) which operate as follows: The High On switch turns on the furnace blower when the temperature reaches some value (usually about 120 degrees F), the second low off switch turns it off when it reaches some other value (typically 80-90 degrees F), and the third sensor (typically 180-250 degrees F) is the high limit protection switch which directly turns off the main gas or oil valve to shut down the burner. This final switch should generally never be tripped. Finally, when the thermostat no longer requires heat, it drops its heat request, shutting down the burner. Since the plenum still contains latent heat from the burner, it will continue to run the fan until the low limit sensor turns the fan off.

With this simple explanation, we can see that the plenum system doesn’t actually know or care (yes I’m anthropomorphizing here) where the heat comes from; so, if you connect the forced air out of the wood/corn/straw burning device, into the furnace plenum, the plenum will automatically turn on and off in response to the heating of the air, regardless of where the hot air originated. You may have to place a gravity damper, or and electric damper connected to the alternative heat blower motor control to act as a check valve and ensure that heat doesn’t flow backwards through the secondary heat plenum when it’s not running. When no alternative heat is being produced, the conventional furnace operates normally.

I’ve installed this system in homes of several friends over the years, and it works quite well. – LVZ in Ohio