I've been doing some reading, lots of reading, LOL, and came across an article saying that home designs like ours, two stories with a vaulted entryway and staircase are a nightmare for HVAC. It recommended two systems: one up, one down for real comfort and said it was really more economical than a two-zone single system. We've thought about putting a second unit in the attic, but it's something that probably has to wait until the house is paid off. In the meantime, I've been thinking and finally realized that there is a place we could put another supply duct. It would be on the far side of the door into the garage. The current duct trunk is on the other side of that door. It's right above the closet in the guest room, so we should be able to go through there and straight up to the attic--hope the attic joists aren't in the way. The run would be about 10"-11" x 24" in size and approx 58' long with 2 right angle turns. We're thinking it could handle about 900 CFM and hoping we could take our master bedroom and vaulted ceiling bath off the current duct and supply them with that. Our bedroom gets a little, but our bath is at the end of the current run and gets basically no air. With our master suite off the main trunk, I'm pretty sure the other upstairs rooms would have plenty. Does that sound like a duct that would work? Hubby is also thinking that if we did it with ductboard, he'd be able to do most of it himself, except for the connection to the plenum. He's pretty good with carpentry, plumbing and electrical, but has only worked on a/c in cars. And if I hadn't mentioned it, after measuring our house, we're really around 2,600 sq ft, not the 2,400 sq ft we had thought we had. Sorry, one more thing, if we have 1410 CFM now and add 900 CFM with another duct, going to about 2500 CFM, does that mean we'd need any certain blower size? Or do we just go with what the manual J says, assuming I can find the manual or a tech to do the calcs for us?

Yes, it's probably a scam. But you may have an issue with the gas valve, burners, or the exhaust being restricted. When you have a cracked heat exchanger, it's potentially very dangerous if you also have high CO in your system's exhaust because a crack could let exhaust gas into your home. Replacing a heat exchanger has no effect on the CO levels in the exhaust plenum of your furnace, it only isolates the exhaust from the inside of your home - in your case, that's already happening (from what you wrote, it sounds like the high CO is only in the exhaust which means the heat exchanger is OK). High efficiency furnaces and boilers save energy by condensing hot exhaust instead of sending that energy out a chimney. The liquid that is a result of this energy saving process is very acidic and, while careful selection of materials slows the process, that acid inevitably shortens the life of the furnace. At 22 years, you're going to need a new furnace soon, but you may want to explore getting it from someone else. It's possible that you misunderstood what he was telling you. If not, then you need a different tech because this one doesn't know enough about furnaces and how they work.

The biggest problem with HVAC zone systems is knowing when to choose it as a solution and when not to. Some HVAC companies it's about "sell, sell, sell" whether or not it works... there's more money in "sell, sell, sell" --- when it's only about money? So does the comment above mean I do it for free? No. If you think that you are reading things that aren't there. New construction? best to choose separate systems 9 times out of 10. In order for a zone system to work, you have to know what you are doing. Most HVAC companies staff (the techs they send you) are 20-30 year olds. How much practical experience could they possible have? It's best for HVAC zone systems to be an elegant solution. A HVAC zone system is a tool in the tool bag. Not all homes are suitable for zone systems. Some homes there is no other way, and in some cases complications to those problems will make an HVAC zone system design possibly more prone to problems. You have a problem now, do you want more problems. These decisions among others are decided "in person" --- so considering that becareful what information you decide upon from the internet. Just because it's here doesn't necessarily mean it's true. That said: Depending on equipment level chosen, how many different floors you have in your structure, how much room you have available... will all be factors that make you decide one way or another. From there it's in your best interest to pick a contractor that is skilled: especially when it comes to HVAC zone systems. (there's a lot of garbage out there.) (click to enlarge if necessary) I service the Katy, Texas area.

A few things... - Eliminate straight in line connections. This may sometimes require an extra couple of bends to create offsets. - Insulation within the ducts. - Silencers (e.g., from Fantech) work quite well. - Hang duct w/ perf strapping and don't let duct or fittings come in contact w/ framing or structural members of the house. - Insulation in walls. - Hang drywall w/ iso-channel, or do double layer w/ green glue or use pre-made acoustic drywall. ------------- Also (reduce noise at source!): - Sound damping materials in rooms that will have a lot of noise or that you want to be quiet. - Eliminate parallel surfaces. EG, ceiling sloped 5° so it's not parallel w/ floor. Opposing walls similarly un-parallel by a few °.