Duct clearances to combustibles

[DoubleB]

Hi All,

I’ve been lurking a while, first post now. We have a 2800 sq ft old farmhouse. 1100 sq ft on each story, plus a 600 sq ft room above the newer garage addition. The forced air ducts were added some decades ago so I hear. Fuel oil furnace with a/c coil over the top. Spending way too much on fuel oil and it’s time to go with (primarily) wood heat. Based on what I’ve read on here, this is my plan:

-Get a PSG Caddy with oil add-on for backup, putting both on my single 7” chimney flue. I already called the insurance co, building inspector, fire dept, and potential installer, and they all are ok with this since it’s per PSG instructions.

-Shield or remove the a/c coil from the furnace to withstand high temps in a power outage.

-Get a liner in my masonry chimney. Might not be required, but worth the money. My chimney is 35 feet.

I have two questions:

-It’s very important to operate in a power outage. I can't find a convincing answer about duct clearances to combustibles. The PSG manual, and other posts on this site, say keep ducts 6” from combustibles for 6’ from the furnace, then 1” from combustibles thereafter. Each of my ducts and/or registers goes through a combustible floor or wall, one duct does so 3 feet above the furnace. The potential installer said that ducts can touch combustibles, and the 6” for 6’ then 1” only applies to the main plenum. Is that true? Even if so, is that a good idea? So what’s the real scoop on preventing hot ducts from burning down a house in a power outage, or dealing with/interpreting the 6” for 6’ then 1” rules?

-Anything else I’m missing for the whole picture of installing the furnace?

Thanks much!

 

[laynes69]

Unless you've done extensive work to your home, I wouldn't install a Caddy. The Max Caddy would be a better fit.

Gravity heat is only as good as the ductwork. A system designed to have gravity heat would have oversized ducts with few bends. The large plenum opening would accommodate much better also. Your duct clearances are for your main trunk off the plenum. Heat will only go so far into the system during an outage and dissipate. There's a reason for the clearances, I'm guessing the hottest point of the system is within the first 6 feet. Your main trunk will contain most of the heat, those outlets off those shouldn't be as hot.