Seeking Guidance on Furnace Install

[SeanS]

Hi All,

Thanks again for all the wonderful info on this site...I have received some valuable insight form previous posts, but my install has hit a bit of a snag and I'm hoping someone can steer me in the right direction.

I have a Harman 2500A (1000 CFM blower, 120,000 BTU, 20 X 20 Plenum) that I was hoping to tie into my existing duct. I have had a couple HVAC guys out, but they seem to be a little overwhelmed by the project. While they have admittedly only dealt with smaller wood furnaces, their fear is that my stove is too big for my existing system. Perhaps this is the case and the dealer sold me more than I needed...now I basically just want to figure out how to start heating with wood and ensure I don't have an expensive paper weight in the basement. My house is 3300 sqft (new construction)...though it is 2 zones and the duct I want to tie into feeds about 2000 sqft.

Any insight to the following questions (or any additional info you feel would be beneficial) would be greatly appreciated

1) If anyone knows of an HVAC guy that's experienced with these types of installs please let me know. I live in Southern Massachusetts (Town of Rehoboth)

2) The concerns from the people that were out were in regards to the size of my supply trunk (i.e. afraid my furnace might overpower my existing duct). With a 20 X 20 plenum on the furnace, what size duct do I need to feed into. Does it need to be at least 400 sq inches to match the plenum, or is there some ratio to determine the minimum size.

3) If the size of the supply trunk is a valid concern, could I help to alleviate the issue by trunking off the plenum into 2 feeds. I could have half (or the appropriate size) of it feed into the supply trunk, and the other half feeding to a dedicated register. I know this would pump a lot of hot air in one room, but with my limited knowledge and lack of options from the HVAC people I'm grasping here.

Any other thoughts...I know this may not be ideal and that I may have gotten talked into the wrong system but I would like to find a way to make it work.

Thanks for your input and Happy Holidays!

Sean

 

[brenndatomu]

Hi Sean! Yep, it is usually hard to find someone that is willing to install a wood furnace anywhere, I had the same issue on my Yukon. I did the install myself, had my neighbor do the ductwork fab for me, I was lucky to have him, he does it full time for the local HVAC co, he's really good! Good thing, cause the duct/plenum/adapters were complicated!
Anyways, no, you don't have to have 400 in of duct. Most furnaces of that BTU size have (2) round 8" ducts coming off them. Some of the better built ones (especially if they can burn coal) have larger plenums so that they can gravity heat with power out and not overheat (if the duct system is built correctly) I know the Harmans are a big brand with the Amish, probably for this reason.
I'd build a 20x20 plenum, and then come off the plenum with round or rectangular ducts as needed, then put a safety heat dump, like this one,http://www.yukon-eagle.com/LinkClick.aspx?link=200&tabid=189 to make sure you don't overheat on power loss/blower failure.
Keep diggin, you'll find a tin knocker that can handle the job! The dealer you bought the furnace from doesn't install or recommend installers?
Pics would be good for more/better advice....

 

[SeanS]

Thanks for the info...I'm glad my situation does not seem completely lost. I've had a terrible time getting any info from the dealer...I will keep trying but it seems only the owner will be able to tell me more than "check the manual." Might try another local dealer too and see who they would recommend.

That heat dump seems like a good idea...perhaps it would help to alleviate some of the concerns from the guys that have checked it out.

I'll post some pics in the morning...

Sean

 

[laynes69]

While I'm no hvac expert, I have our furnace tied into an 8x18" trunk, and our plenum is around that size, plus our furnace has a 1300 cfm 4 speed blower. What's important it to maintain clearances in your ductwork, and have enough return on the woodfurnace so it doesn't overheat. Where things get tricky is with your backflow or backdraft dampers. You want to isolate the operation from your current central furnace. They both should share the same ductwork (must be all metal), so more than likely it will be a parallel install (side by side). When you say your home is 3300 sqft, does that include the basement, and how well is the house insulated? Just getting an idea on your setup. Make sure the installers follow the manual exactly. More than likely your insurance co. will want the install verified with the manufacturer of the furnace.

 

[SeanS]

Good to know...I believe my trunk is 10x17"...not positive since it is insulated. I would prefer to do a parallel install and one area the HVAC guys were sure of was the need for the dampers so I will be sure those get installed at all the necessary spots. I would also like to have a dedicated return air set up that will supply outside air.

The 3300 sqft does not include the basement. As far as I can tell it seems to be well insulated. I am in the process of re caulking some gaps on the window sills. The outside walls are 2x6 studs, so that should provide a little better insulation that 2x4. The attic was well insulated, and the ceiling of the basement is fully insulated as well (in addition to all ducting coming off the main furnace) so that would lead me to believe the overall insulation is fairly solid.

 

[laynes69]

Sounds like everything is okay then. Just follow clearances and you'll alright. Your ductwork is more than capable of handling the wood furnace.