Pointedstick wrote:
jafs, if you have ducts in the attic, that's probably part of the problem. The attic is outdoors. The outdoors can get wet and grow mold, and it's more likely in a rainy climate like Kansas than it is in bone-dry New Mexico where I live. The fact that your guy sealed the ducts (with aluminum tape) means they were un-sealed before, which means they were leaky. They probably still are leaky, too. Most duct systems are, and especially most duct systems in the attic. The correct procedure to seal duct seams is with duct mastic, not foil tape, which eventually falls off.
Also, CO monitors are not actually all that useful. You see, they're programmed to ignore a large buildup of CO that dissipates over the course of a few minutes. Why? Because this is what all gas ovens do, and every time you turned one on to bake something, your alarm would beep and you'd freak out and evacuate the house. And for good reason! You're being poisoned! But this kind of poisoning is so commonplace due to the way gas ranges work (un-ducted with combustion by-products dumped into the house air) that it was decided that the detector should only detect conditions out of the ordinary--which means a sustained high level of CO that indicates that something's continuously spewing a high level of CO into the air. The monitor allows you to be slightly poisoned, but not majorly poisoned.
So your detector wouldn't necessarily go off if your gas furnace is leaking CO; the initial buildup would quickly get diluted throughout the house, and after the furnace turns off, the natural air exchange between your house and the outside (I am assuming you don't live in a Passivehaus with an ACH50 reading of < 0.6 pascals) would cause it to fall and the CO monitor might mistake it for a gas range doing its normal thing--only poisoning you a little bit.
The only real way to be sure is to buy a low-level CO monitor that actually displays the instantaneous reading of the CO level. These are expensive, $250 and up. I recently decided it made more sense for me to replace the gas appliances with electric ones that produce no CO rather than invest in more testing equipment to determine just how much the appliances are poisoning my family.
In much of Kansas, replacing the gas furnace with a heat pump makes sense, especially if your system includes air conditioning. One machine does it all, and most of the state has a climate mild enough for it to work well. But do check all the areas near your ducts, air handler, and register for mold, dead animals, mouse poop, termite colonies, etc.
</amateur building scientist>
The return air ducts are in the attic, and the heat registers are in the floor, with the ducts in the crawl space - we have a "downflow" system.
How is an attic outdoors? We have a roof that protects from rain, don't we? There are vents on each side and some in the roof to allow for air circulation, which seems to be the right thing to do. There was mold from some strange stuff before - the bathroom vent fan was venting directly into the attic. But we had them treat that when we bought the house, and our inspector checked it out before and afterwards and said it seemed to have been fixed. And, of course, we installed venting to vent the bath fan out of the attic.
Since the furnace/ac system is young, I'd hate to replace it with something yet - we should be able to get a lot more years out of it. But I've thought about a heat pump system, for sure - there are a lot of things I like about them.
Whenever our great handyman/contractor guy has been under the house, we ask him to check out the conditions there, and he always says it looks good and clean to him.
Don't the HVAC companies check for leakage of CO and/or CO2 as part of their annual checks?
We have a gas stove, but don't use the pilot light, and just use a lighter to light the burners when we use them. And we don't use the oven at all.
Experts? Yeah, right!
