Question about BTUs vs Sq Ft

[newhomesteaderpa]

Hello!

I apologize if this is a newbie question, but I can't seem to find the answer despite searching.

I'm still doing (very preliminary) research, and I ran across two stoves with vastly different BTUs vs the area they are supposed to heat.
US Stove - 900 Sq Ft, 54,000 BTUs : US Stove, Menards
Morso 2b - 1200 Sq Ft, 25,300 BTUs : Morso 2b

Can anyone help me understand this disparity? I understand the BTU ratings can be ... unreliable, but this difference is huge.
Is either one accurate? Is this a difference in design? US vs European manufacture?

I found this conversion chart: BTU Chart
But I have a space about 1,250 sq ft, which would indicate around ~55k-70k BTUs... which doesn't fit either stove!

Thank you for your help!

 

[kborndale]

You have to take btu ratings with a grain of salt, especially saying this many BTUs will heat this many SQ ft. 25000 BTUs may heat 1200 SQ ft when it's 35 degrees in a well insulated house while 54000 may not heat 1200 SQ ft in a poorly insulated house in the teens. There is not a standard to go by, each manufacturer pretty much makes up their own rules on it.

 

[newhomesteaderpa]

Thanks kborndale!
So,... maybe as a general rule of thumb, take the smaller of the measurements as the "safe harbor" heating capacity?

Like, the US Stove should at least be able to heat the listed 900 sq ft, (as opposed to the ~1,000 sq ft its BTUs would indicate)
and the Morso 2b should put out ~25k BTU, which according to the chart would heat around ~500 sq feet? (Not the 1,200 indicated!)

This might mean the Morso 2b is very over-estimating the square footage it can heat, while the US stove is about accurate in the Sq ft compared to BTUs? (All things being equal) Not a specific comment on these brands/stoves.

Does this sound like a good starting point for comparison and estimating?

 

[stoveliker]

Those numbers are marketing and not engineering. The error bar is at least 75% of the value of the number...

To get better advice, it would help to provide a sketch of the floor plan; sizes, walls, (door) openings, and ceiling height.

What do you want to heat: tv room, one floor, whole home? Continuously, or only evenings, or only weekends? Only wood or as supplement to e.g. oil?

Second, do you have a chimney? Is it lined with an insulated liner (you'll most likely have to do this for code and safety)? Have it inspected by a professional for integrity and issues before you burn. How tall is it?

Do you have wood already stacked and drying? Modern stoves want dry wood, as in 20% or less moisture content. That takes at least (!) a year for most wood, and likely 2 for oak. I am on a 3 year drying schedule. Get wood stacked off the ground **now**, covered, facing sun, and seeing wind. Cherry, pine, maple if split small, are your best bet if you have to start now and want to have suitable wood coming heating season.

 

[newhomesteaderpa]

Thanks! I appreciate the advice.
I am hoping to heat a wing of the house, about 1,070 sq ft. Ceilings are 8 ft. Insulation is average?
I live in PA, and I'd like to supplement the existing heat pump/use in the case of losing power/extremely low temps as a stopgap.

The black rectangle in the hallway is the planned placement of the stove.
The alcove is only 2' x 3' - so you can see why I am looking at these tiny stoves.

We would run a new chimney, and install some sort of venting to draw the heat from the hallway into the bedrooms.
Suggestions appreciated, I am concerned with how "chopped up" the space is and how the heat would travel.

Thanks!

 

[begreen]

There is a big difference between the EPA tested heat output of a stove and marketing numbers. Morso's are the former and the US Stove numbers sound strongly like the latter. They are probably peak output numbers.

Heating from a hallway is going to have mixed results. The hallway will get hot, but that does not ensure good heating in the bedrooms due to convection issues. " install some sort of venting to draw the heat from the hallway into the bedrooms" - What are the thoughts here?

What is under this section of the house? Is there a floor below this where the stove could be located? That might ensure more even heating.

 

[stoveliker]

Any "venting" would likely have to be done by blowing cold air to the stove from the adjacent rooms. I.e. a fan on the floor in every door opening blowing slowly towards the stove.

Or better some thru the wall fans.
But it's going to be hard, as begreen says.

 

[newhomesteaderpa]

RE: Begreen - I somewhat suspected the US Stove numbers were inflated, but I was hoping with that price tag the "too good to be true" numbers were actually true.

This section of the house sits over a crawlspace, unfortunately.

RE: Begreen & Stoveliker - Yes, the idea was to install some through the wall fans/vents to draw warm air into the rooms from the hallways.
Something like: ThruWall Fan installed above the doors to the bedrooms, blowing rising warm air into the rooms, with cold air dropping and exiting under the door through the gap between the door and the floor back into the hallway. Does this sound like it might work?

Do you have any other ideas that might better circulate the air through this wing of the house?
Thanks for all the help!

 

[stoveliker]

I would instead have those fans near ground level pushing cold air to the stove, and cracking a door to let warm air in. Moving cold air is easier.

 

[begreen]

With three of those fans running it's going to sound like a beehive. Is this a tri-level where there is a living area down the steps? If so, heat will convect up from the main area if there is a stove there. The rest is up to the quality of insulation in the bedroom level.

 

[newhomesteaderpa]

Stoveliker - If you put a fan on the floor blowing cold air, how do you keep the rooms warm when the doors are closed? Or do you just default to the doors always being open?

And, "Moving cold air is easier." - Is that because you can blow it, whereas hot air you have to suck away from the stove?

Begreen - The house is all one level, this is a separate "wing" with all the bedrooms. And I prefer to think of the fans as a pleasant hum. :D
I will try to get ones with a low noise level, but I think the end result either way will be one big fan or a couple small ones.

 

[stoveliker]

You need to have flow of air, the best way to do that is to have an entrance and exit point, so yes, keep the door cracked open if you put a fan in a wall.

If you put a fan on the floor in the doorway opening it needs to be even more opened.

 

[stoveliker]

With the fan on the floor in the door, you need to run it on low, otherwise the air mixes too much. Keep a cold air flowing out at the bottom and warm air in to replace that at the top. Keep it stratified.

With a fan in the wall a bit away from the door you can run it harder.

 

[newhomesteaderpa]

Ahhh. I can see it now.
That makes sense. Thank you!

 

[kborndale]

Your really just using the fan to create a convection loop. Cold air is more dense so it's more efficient to push the cold air towards the stove room.

 

[begreen]

It looks like there is a 2-3 step stairway up to this area showing at the bottom of the image. Can a stove be placed opposite this area? If it had a blower the convected heat could be directed toward the hallway.

 

[begreen]

See comments in second thread

Recommendations for a small Child-Safe hallway stove/insert/fireplace

Hello! I would appreciate some recommendations for a wood burning stove in an area of new construction. The planned placement is in a hallway (see below - the solid black rectangle). The wife is concerned about the kids burning themselves on a freestanding stove as they walk past and we're...

www.hearth.com

 

[Woody Stover]

"Moving cold air is easier." - Is that because you can blow it, whereas hot air you have to suck away from the stove?

Your really just using the fan to create a convection loop. Cold air is more dense so it's more efficient to push the cold air towards the stove room.

With the fan on the floor in the door, you need to run it on low, otherwise the air mixes too much. Keep a cold air flowing out at the bottom and warm air in to replace that at the top. Keep it stratified.

Right; Your aim is to enhance the convection loop that's already happening naturally. You can feel this in any room with exterior walls; The cooler air falls downward off the outer walls, then flows across the floor toward the center of the room, displacing the warmer, lighter air upward in the center of the room. As stoveliker says, you just want to gently boost that, not have so much air blowing so that it disrupts the natural stratification.
We use this mini tower fan not to move heat, but to cool our "hotdog" when he's trying to sleep; He likes it a bit cooler than we do. 😏
It's only about a foot tall and has a small footprint, so it isn't in the way as much as an 8" fan might be. It doesn't move a whole lot of air, but might work well enough moving cool air out of a bedroom back into the stove room without having the door all the way open. It's very quiet as well, compared to the 8". I use a couple of regular size ones as well when I'm not running the AC, and it might be slightly warm and humid...one at my computer desk and another at the recliners by the TV.

 

[Poindexter]

A useful thing here is the historic heating bills over the last couple years. Besides boiler fuel, look for spikes in the electric bill suggesting electric heaters were in use. Do you smell kerosene exhaust anywhere in the house suggesting off books BTU consumption?

Once you know historic boiler fuel and wintertime electric usage you can get a handle on BTU requirements for the envelope you have, but you will never really know how warm the previous owners kept the space.

With a chopped up floor plan like you have supplementing the HVAC system you have with a wood burner is about all you can do, and the greyed out area is as good a location as you can hope for.

Best wishes.