Looking to install add on wood furnace.

[zpollard88]

I am new to the site, I have been looking at it for a couple years doing research into getting an add on wood furnace. I appreciate this website and enjoy reading the articles. So thank you!

I have arrived at a point that I am not sure which way to go. I have researched and not been able to come up with any similar set ups. So, I will give all the information that I have and ask for some advice around the situation...

I have a 1600 sq foot 2014 Redman MODULAR home, (not a double wide) on a full ICF foundation, there is no attached frame. It is a one store house. I currently have a 95% efficient Nordyne M7RL down-flow LP furnace installed on the main floor. I am looking to purchase a Napoleon HMF150 Hybrid wood furnace as a stand alone unit, It will be installed in the basement, nearly directly under my existing. I am trying to figure out how to tie my new furnace into my existing duct work. I have a chimney chase ready to go, I am most likely going with a metal chimney. Does anyone have anything close to this setup? I have been talking with a gentlemen from a stove shop in my area and he is telling me that I may need to upgrade my existing duct work?

If anyone has any insight or advice, comments, or anything. Please let me know. I am trying to figure out the best way to go about this. Thank you!

PS I have already checked with my insurance company and they are all set with me installing a wood furnace.

 

[Owen1508]

Is it because of the current duct size or another issue with the duct work? Pictures always help

 

[zpollard88]

It is the duct size. It is potentially not big enough to hand the load of the wood furnace. I would think as long as I have a one way damper set to they don't feed into each other I should be fine right? I just want to make sure that I don't need to spend more money than needed if my existing duct work will work just fine.... Here is a picture of where my furnace feeds down to my duct work and where I would like to potentially tie it in.

 

[begreen]

Yes, we need more information. If you can tap directly into the supply and return trunks then the modification may be limited to installing backflow dampers.

Edit: That is an odd ductwork plenum. Who installed this furnace? What is the trunk duct H & W?

 

[begreen]

Also why the insulation under the ductwork if this is on an ICF foundation? Isn't the basement fully insulated?

 

[zpollard88]

It is that is a vapor barrier from transport that I haven't removed yet. The duct-work was installed at the factory. the measurements are 5x14 roughly..

 

[begreen]

5" x 14" is tiny. This is a small gas furnace. What is the BTU output of the furnace? Are you sure you want to put something as powerful as the Napoleon HMF150 in the basement? With an average output of 70K BTUs looks like it would cook you out of the place. I would consider some alternatives.

 

[zpollard88]

my current furnace is a 75k btu unit

 

[begreen]

Something is still not adding up. Are you sure about the trunk duct dimensions? It's hard to see the trunk duct. It may be the photo but there appears to be an upper and lower section with a seam in the middle. The upper part appears to be reflecting the joists. Is this correct? If so, it looks much larger than 5" high. But again, this could be a camera illusion.

my current furnace is a 75k btu unit

What is the full model designation of the furnace? Is this the M7RL072A?

 

[firefighterjake]

Just curious why you have opted to go with an add on wood furnace instead of a stand alone woodstove.

I almost went that route myself.

 

[laynes69]

You'll cook yourself out of your home. Our caddy has a similar firebox/setup to the napoleon and we heat a much larger older home. If you want to go the woodfurnace route, then maybe a mini-caddy. Even though your central furnace is 75k btu, you will rarely if ever hit the maximum output of the furnace. My brother has a manufactured home, and I know for sure shortcuts were taken and hidden under the insulation, including disconnected ducting. If everything checked out okay with clearances and duct condition then backdraft dampers would need to be installed to isolate the central furnace from the woodfurnace. A woodstove that's sized correctly shouldn't be ruled out.

 

[begreen]

The M7RL072A is a 72KBTU input, 68K output furnace. The important difference between it and a wood furnace is that it cycles. When the thermostat's demand for heat is satisfied it shuts off. Not so with a wood furnace. It will continue to dump out heat at a steady state. For the HFM150 this is about 70-80K BTUs continuously which is enough to bake the main floor. It seems like the HFM100 would be a better fit with about a 35-40K steady output, but first we need to know more about the general plan. For example, is the intent to also heat the basement? If so, how many sq ft is the basement? With ICF walls it shouldn't take much and heating the basement will reduce the amount of heat needed to keep the main floor comfortable. A decent catalytic stove might be an alternative. If dead set on a furnace I would consider a pellet furnace instead. It can cycle on and off like a gas furnace.

 

[zpollard88]

I am doing a furnace because I have free fire wood. I plan on heating the basement as well. It is a 28x60 basement. Yes, that is the main trunk coming off from the furnace at that point. It may get larger or smaller I am not sure. I want the furnace because I want to distribute the heat through out the house. Maybe a smaller unit is a better option?

 

[begreen]

So 28x60 with ICF walls. That would bring the heated area up to 3200 sq ft. Is the floor insulated too? You might get away with a stove. It depends on how the heat gets upstairs. Is there a stairwell near the new basement chimney location? What is the upstairs floorplan like, open on one end and bedrooms off of a hallway on the other end?

The reason for the questions is that I am exploring a couple options. One being to use the furnace blower to circulate heat (probably not, it's noisy and the return is on the top of the furnace) and the other is to locate a fan that pushes heat up on one end and a return grille on the other end that allows it to come back. This is a good situation for a large cat stove like the BK Princess or King if the circulation issue can be solved reasonably.

The HFM150 furnace might work out with its own plenum and a splitter that dumped part of the forced air heat in the basement, but it could be hard to run in the milder weather without baking the house. Wood furnaces tend to burn hot or not, they are more steady state heaters. And ICF walls are pretty good at containing heat. A smaller furnace like the mini-Caddy or the HFM100 looks like it would be better sized. albeit with a shorter reload time. There still would be the need for backdraft dampers to be worked out.

 

[zpollard88]

I have an open concept upstairs, two beds on the ends and one master suite on the other. The stairwell up stairs is about 20 feet from the chimney and stove, it is also facing away from where the furnace will be.

 

[begreen]

Sounds like it would also work with a wood stove and circulation help if the furnace doesn't work out.

 

[zpollard88]

So how would I circulate the heat to the upstairs without cutting holes in my floors? Sorry for the delay, we've been away on vacation...

 

[begreen]

Some folks raise the temp in the basement to 85F to achieve a 72F upstairs temp via the stairwell convection. Not sure if that would work for you or not.

 

[zpollard88]

Should I make a couple grates in the floor?

 

[begreen]

If the basement is wide open then a floor grate at the opposite ends will aid heat convection. They should have fusible-link dampers as this is a floor penetration. Atlanta Supply Co. sells the dampers and floor registers.