Adding external blower to BIS Nova

[shyland83]

I recently installed a BIS Nova zero clearance wood burning stove at one end of my house in the living room. It is about 50 ft to the other end of the house where the bedrooms are. It gets a little chilly in the bedrooms when the stove is running so I would like to get some warm air down there. I started hooking up 6" flex lines to the central forced are knockout on the side of the stove. It is intented to blow air from the stove to another part of the house using a duct fan. As I was installing it I had an idea that I want some opinions on.

I want to run the duct to the bedrooms at the opposite side of the house but turn the fan around so it blows air into the stove. Here is my reasoning. This will allow me to use the duct fan to blow air out of the front of the stove. This will replace the built in blower fan so both do not need to run at the same time. It will also be quieter because the fan will be in the attic instead of in the stove. Pulling the air in from the opposite end of the house will cause warm air from the living room to be drawn to the bedrooms. I am also worried that if I try to blow hot air to the bedrooms by the time it makes it 50 ft through the attic it will cool down significantly.

Hopefully that made sense, if not let me know i will try to clarify. Does anyone see a resaon why this is a bad idea or have any input at all? Thanks.

-Scott

 

[babzog]

Can't speak to register temps, but I avoided those dealers who suggested putting the heating ducts into the attic. First and most importantly, you are putting warmth into what is supposed to be a cold space. Ice dams, etc are potential problems you might encounter. Another issue is, you are cooling your warm air by running it in a cold space, eliminating efficiency. Further, you will lose a lot of heat to unsealed ductwork. You can help all this somewhat by sealing and insulating (very well!!) the ductwork and the attic penetration points, but why go to that work when you can and should run the ducts inside the building envelope. Any heat lost from the duct is lost into your home.

I was cautioned against the BIS for my application, only due to the smaller 5" heat duct and smaller cfm blower fan. I too had about 50' to go and was told I wouldn't get the performance I was after. Perhaps if you are just putting in one run (I was looking at a dedicated trunk plus 3 registers) it would work alright. If it were me, I'd duct the heat directly to the cold room. The heat that is pulled off the fireplace is pretty impressive (was 50*C / 120*F when I checked the other night), so, even if some is lost heating up the duct, that blast of heat is going to persist for hours, depending on your burn.

Or, hook up the heat duct to your hot air plenum and run the furnace fan to distribute the heat throughout the house. That's the route I pursued and should see final hookup next week.

 

[shyland83]

-Running the duct inside the house is not an option, the attic is my only choice

-I considered tying into the return plenum but it's only the 2 bedrooms at the far end that get cold, its an open floor plan everywhere else so there is no need to pump hot air to those rooms.

-I do plan on Insulating the duct well in the attic, I guess i could try it and see what the temp is coming out after 50 feet. I could always turn the fan around later.

A big part of my reasoning behind blowing air the other way is both to save the electricity of running 2 fan motors at the same time(We pay over 20 cents a Kw hour here, so every little bit of saved electricity helps) and to make it quieter in the living room. The stove is right next to the TV and although the built in blower fan is not extremely loud it is a little annoying.

 

[mikeyd]

I had some of the same considerations on a recent install of my Lennox Ladera (same as NOVA). I didn't end up installing the forced air option as I was constantly told I'd be disappointed with the results. There was a poster on hearth who was a dealer and also suggested that the forced air and gravity vents are not top performers so-to-speak - hopefully he will chime in - his name was Gary I believe.

A couple of things to consider (whether they are of any material signficance or not is up to you I guess but will allow to continue to research).

1) the forced air option will now make your stove non-EPA compliant I believe
2) drawing all the air out of the stove using the FA option, as it's intended, will cool the firebox making it harder to maintain optimum temps is what I was told. I would suspect blowing air towards it would also contribute to this problem and perhaps even compound it if it's in fact true. With a ~2.0cu/ft I can see how this might be an issue.
3) not dismissing your Kw costs, the blower I believe draws 2amps (I could be wrong) so is not that much considering the amount of heat it's helping to get out of the stove

In the end it sounds like your trying to get some convection going ? For my application that continues to be a problem as the master bedroom sits adjacent to the room with the fireplace and is always cool. The upstairs rooms with a loft and vaulted ceiling are always warm. I actually did something similiar to your suggested set up but did not attach it to the stove. I placed a register in the MBR and one in the adjacent room with the fireplace on a separate blower that I will turn on once the FP room is up to temp. The ducting runs underneath both rooms and still in the buildng envelope which was helped with getting warm air into the MBR by pulling the cold air out.

One other option to consider, albeit a hydro hit as well, is to use a blower cycling thermostat. The CAG1500 from Lux will let you cycle your blower only from your furnace. Once I installed I seem to get much more even heat. It will cycle the furnace fan only up to 12 mins every hour - I set min to run 3 mins every 15 mins.