Heat circulation

[Ashful]

I'm not sure if this is the correct forum for this question, but since it is ultimately about wood stove sizing and installation, I'm posting it here. Please feel free to move the thread if I have chosen the wrong forum.

We're looking at adding a second wood stove to our home, and are getting a wide range of opinions on sizing and circulation. This is a 1770's farm house with two cooking fireplaces, one being part of the original house and the other being part of the original summer kitchen, the latter now being part of a newer open floorplan addition to the main house.

The fireplace in the newer addition (old summer kitchen) already houses a Jotul 12 Firelight, a catalytic predecessor to the current Jotul F 600 Firelight, rated at 81,500 BTU. It's a monster of a stove, heating a space of only 1100 square feet (the newer addition), but between the non-ideal location (inside an existing fireplace, where circuilation is limited) and the high percentage of glass in the addition, it seems appropriately sized. There is currently no fan or rear heat sheild on the stove, to aid with circulation or directing radiation, but there are two ceiling fans in the room with the stove for general circulation in that end of the home.

The fireplace in the original part of the house is in a small room of only 200 square feet, which is adjacent to two other rooms (160 & 430 square feet) and foyer, making a total of 872 square feet interior space. I'm going to attempt attaching a quick floor plan sketch of this portion of the house below.



The exterior walls are all 18" thick stone, with plaster directly applied (no insulation), as is common to old farm houses in eastern PA. All windows (shown as rough openings in my sketch) are well-maintained 1770's double-hung, with modern storm windows, and can be considered to perform as the average modern double-pane replacement window.

We intent to circulate air from the 200 sq.ft. room containing the fireplace to the other rooms using a powered duct installed across the stairway, as shown in the sketch, forcing air from ceiling level in the small room containing the stove to floor level in the larger room separated by the stairway. Return air will be natural thru the doorways between rooms.

Meeting a representative from our local Jotul dealer at a recent home show, we received the recommendation to buy a stove for not more than 800 square feet heating capacity, given that it was to be installed in a room of only 200 square feet, and we would not want to have a too-large stove running so far below capacity on an on-going basis.

Upon visiting their store a few weeks later, we received a recommendation from another salesperson that we buy a stove sized for heating 2000 - 2500 square feet, and include a rear heat shield and blower kit to boot. Their reasoning was that the stove was to be installed in an existing fireplace, with a large mass of stone to heat, the overall interior square footage (872 sq.ft. net), and the thick un-insulated stone walls.

I suspect the ideal size may lie somewhere between these two extremes. Can anyone offer some guidance? We are also interested in opinions on a recommended CFM range for the blower to be installed between the 200 sq.ft. and 430 sq.ft. rooms.

We currently heat this portion of the house with oil, typically heating it to 70F for a few hours each evening, and otherwise at a constant 62F. There are bedrooms above, which are heated to 65F overnight and 70F each morning, but are otherwise at a constant 62F. They will receive some conducted heat thru the floors, but we have no plans to provide active ventilation between first and second floors.

We have not really figured out what would be the best burning schedule, for this portion of the house that sits empty at 62F for a very big majority of the day. Our primary objective is lowering the oil bill as much as possible, while enjoying the ambience of the stove. I am currently heating 1100 out of 5500 square feet with wood, and keeping up without trouble. If we can shift that up to 2000 - 2500 square feet on wood, I think I'll have the right balance of savings to convenience for our situation.

Thank you,
Joful

 

[begreen]

I think you should do this as a test. Set up a table or box fan blowing cooler air from the living room into the office with the stove. The fan should run on low speed and be placed low, on the floor. I think you will be surprised how well this will work at moderating the office temp yet improving living room comfort.

I'd keep the Jotul 12 for now. Is there a block off plate at the damper level in the fireplace?

 

[zzr7ky]

I use a tower stype fan from Walmart... works like a champ sending air from the cool area into the room with the stove.

 

[begreen]

The object is to move the cooler dense air which is at floor level. The lower the fan can be the better. If using a tower fan, point it low toward the floor.

 

[Ashful]

I'd keep the Jotul 12 for now. Is there a block off plate at the damper level in the fireplace?

Thank you for your reply! Just to be clear, there are two fireplaces, one in either end of the house. The Jotul 12 is installed in the fireplace at the far end of the house (not shown in drawing), and is performing well. The fireplace shown in the drawing currently houses a 40,000 BTU gas insert, left by the previous owner of the house, which I want to remove and replace with a free-standing wood stove.

I'm not sure what I'll find when I remove that gas insert, but my assumption was that I would be installing an insulated steel liner in the old flue (35' height) and connecting to a new free standing stove, set in the firebox. Here's the few facts I do know on that fireplace:

1. Previous owner stated they had problems with getting the open fireplace to draft, which is why they installed a gas insert. Gas insert has a 4" steel or aluminum flue liner, not sufficient for use on a wood stove.
2. Upper portion of chimney appears to have been rebuilt in brick (would have originally been stone) in mid- to late-1800's. This chimney is large (greater than 6' x 3' footprint at roof line), and houses two flues.
3. Peering thru openings in the gas insert surround, I can see the original fireplace has been lined with brick. This is likely a later modification, as the other fireplace in the house (and other local fireplaces of similar age) are all bare stone.

I suspect the firebrick lining and chimney repair are both part of some later rejuvenation of the fireplace and chimney. It is likely the chimney was re-lined at this time to a cross section too small to draft the 56" wide x 60" fireplace opening, which is why the previous owners had so much trouble getting that fireplace to draft, leading them to purchase the gas insert. The previous owner tells me there is no damper assembly in that fireplace, but I won't be able to inspect for myself until I pull the gas insert out. Assuming the best plan is to install an insulated steel liner bottom to top, most of these issues become irrelevant.

So, there are two primary questions on this new install:

1. What size stove to buy? With one salesman telling me to stay with stoves designed for no more than 800 square feet, and other telling me to go with a stove designed for 2000 - 2500 square feet, I'm not sure which direction to go.
2. How many CFM to push between the room with the stove and the cold room across the foyer. I do like the idea to do an experiment, but didn't want to deal with portable fans for the few months we'll need to see a full weather cycle, prior to installing some permanent ductwork. It would be nice to calculate a number and then install a variable speed blower that can cover 50% to 200% of the anticipated need.

 

[begreen]

BrowningBar has experience here and based on his reports of stoves in stone houses I would say go a size up from the norm for this size space. That would put you in the 2-3 cu ft stove range. I would put in an insulated liner, but downsized to 5.5" based on the height of the chimney. A damper sealing block off plate should be installed, or even lower at the lintel level if possible. If that can't happen get a stove with a blower.

As far as what stove, we need to see a picture of the setup. Ideally you want the stove as far out of the stove as is reasonably possible. Also, do you have a style preference?

 

[Ashful]

A damper sealing block off plate should be installed, or even lower at the lintel level if possible. If that can't happen get a stove with a blower.

What is a damper sealing block off plate? I'm familiar with cable-operated top-mount dampers, and standard fireplace dampers, but not familiar with a lot of other "stove technology".

As far as what stove, we need to see a picture of the setup. Ideally you want the stove as far out of the stove as is reasonably possible. Also, do you have a style preference?

Good point on placement. I actually need to figure out the hearth extension, as the wood flooring currently runs right up to the front of the firebox, which is not going to pass anyone's code inspection. I suspect I'll be removing some flooring and laying a stone hearth extension, which may have been there years ago, and removed by some past owner.

On style, this is the original kitchen of a 1770's farm house, now converted to a formal home office. We'll be going with something on the more traditional side, but haven't really made any formal selection yet. We do like building a fire and getting the place up to temperature quickly when we arrive home in the evening, so soapstone is likely not our first choice. The cast iron Jotul 500 series is attractive, and we already have a Jotul 600 series in the other end of the house that seems to work well, but I could be easily swayed toward something else.

I will try to post a photo of what can be seen with the gas insert in place tonight. It will probably be a couple weeks before I pull the gas insert and dig in further.

Thanks!

 

[begreen]

The 500 would be a nice stove to consider as long as it can be side-loaded conveniently. We need to see the fireplace and have some dimensions here for other suggestions.

Damper seal info here:
https://www.hearth.com/econtent/index.php/wiki/Why_damper_seal_is_needed/

 

[Ashful]

The 500 would be a nice stove to consider as long as it can be side-loaded conveniently. We need to see the fireplace and have some dimensions here for other suggestions.

Damper seal info here:
https://www.hearth.com/econtent/index.php/wiki/Why_damper_seal_is_needed/

The fireplace opening is 56" wide x 60" high, and the firebox depth is 27", as lined with firebrick. I do not yet know if the firebox is wider than 56", until i pull that gas insert, as sometimes the opening is narrower than the firebox in these old fireplaces.

Fireplaces this age do not typically have a smoke shelf, but rather the firebox just tapers up to the flue. They were for cooking, not heating the room, and typically had flue diameters that would make your head spin. My Jotul 600 in the fireplace at the other end of the house has a steel block off plate at the top of the smoke chamber, where the flue starts. It is similar to, but located much higher than, what is described in the link.

 

[begreen]

Is 56 x 60 the gas insert surround dimension? We'll need the actual firebox dimensions, but it sounds like you will be able to accommodate several different stoves.

In this case it's best to drop the block off plate as low as possible to reduce creating a heat trap in the smoke chamber.

 

[Ashful]

Sorry for the confusion. The 56" wide x 60" high is the fireplace opening, which has been framed into 34" wide x 24" high to fit my current gas insert.

Well, curiousity got the best of me, and I just had to pull the insert surround to look inside. The firebox is much smaller than I had anticipated. The OD of the fireplace is 92" wide x 34" deep, but the firebox is built in with brick to 48" wide x 26" deep. The brick work is much older than the gas insert, and shows signs of the fireplace being used prior to installation of the gas insert, but is obviously much newer than the original 1770's construction of the fireplace. I assume that someone converted this from a much larger cooking fireplace to a smaller heating fireplace when the new kitchen was built in 1894.

So, with a 48" wide fire box in the fireplace, it does not appear I'll have much room for side-loading a Jotul 500 or 600. If I decide to stick with cast iron Jotuls, I might do better moving my old Firelight 12 top load cat stove into this fireplace, and putting a side-loader 600 in the much larger fireplace in the other end of the house. Of course, there may be better options.

I'll upload some photos below. Sorry about the quality... some of them came from a camera phone.

Mendota gas insert, as installed:


With surround removed (note lack of hearth extension):


Looking up flue (note lack of smoke shelf mentioned in earlier post):


Looking at back side of upper surround for gas unit, framed with 2 x 4's and covered in ceramic tile on outside:

 

[begreen]

Thanks. The pictures are very helpful. To accomodate a wood stove there will need to be some serious surgery on the woodwork here. Maybe a complete tearout. Is that ok? If not, is there any possibility of putting a freestanding stove in the living room instead?

 

[Ashful]

Understood. A full tear-out is the plan. Depending on the condition of the flue, which the previous owners report as good, I might even try a little open-hearth burning for fun, between tearing out the old gas insert surround and installing the wood stove.

I had also wanted to install the stove in the living room, as that's the largest room, and where we're most likley to enjoy the stove. This part of the house originally had a chimney in each end wall, and I see shadow of the now-covered flue connector in our exterior living room wall, but some previous owner knocked that chimney stack off below the roof line when replacing the roof in the past. I suspect it may have been in poor condition, as it's obvious the upper stack on the one chimney we still have has been rebuilt. Cost to open up the roof, rebuild that stack, and install in the living room would be in the 5-figure range. So, we're considering that as our plan B, only to be considered if we can't make the fireplace install work.

It's amazing to me the hearth does not extend beyond the firebox, with wood flooring running right up to the front of the hearth. By modern expectations, we'd be nervous to use a fireplace like this for occassional use, and we have modern fire companies with pumps and tankers. This fireplace would have been the primary cooking appliance in the house from the 1770's until at least 1894. For at least the first 100 years of that period, this would have been an open hearth, burned nearly around the clock for most of the year. They may have installed a cast iron cookstove in the fireplace in the later part of this period. I believe modern code dictates I will need 16" inflammable surface in front of the stove, meaning I'll need to do some surgery, or install a portable pad. Inspection in the basement indicates there was never any hearth extension, as the fireplace foundation does not extend past the firebox, and the hewn beams on which the flooring sits look original in the location where a hearth extension would have to lie.

I just saw your sketch of air flow on my floorplan for the first time this morning. Thank you for posting that. I had seen the thumbnail before, and thought it was just a mistaken re-posting of the floor plan.

Perhaps I should start a new thread just for stove recommendations? I think the title I gave this thread has many people skipping over it. Now that we've done some investigation behind the gas insert, I have a better idea of what type of stove I need, but still questioning the sizing.

Thanks!

 

[begreen]

I caution against open hearth burning if that chimney is very old, especially if it is unlined. That could be hazardous. Note that the chimney will need to be clean before a liner can be installed.

Based on the depth of the fireplace, if there wasn't a hearth originally, perhaps they burned in the back of the fireplace for cooking only? Do you know what was the original use of this room?

What is above the living room? If you could go straight up with an interior chimney (metal) that would provide the best performance and ease of cleaning. If there is a room above, the chimney pipe would be enclosed in a chase.

 

[Ashful]

I caution against open hearth burning if that chimney is very old, especially if it is unlined. That could be hazardous. Note that the chimney will need to be clean before a liner can be installed.

The previous owners used this fireplace as open hearth for some time before installing the gas insert, but had so many problems with poor draft that they resigned to installing the gas insert. So, it's likely safe for use, but I had not considered the need for re-cleaning if we used it open in the interim.

Based on the depth of the fireplace, if there wasn't a hearth originally, perhaps they burned in the back of the fireplace for cooking only? Do you know what was the original use of this room?

I believe this was originally the kitchen. That fireplace is where they'd have cooked their meals 8 - 9 months of the year. There is a separate summer kitchen on the other end of the house, where I already have the Jotul 12 installed, which they would have used to keep the kitchen odors and heat (and bugs) out of the house in hot summer months. The high count of pie-plate flue holes in the various walls of the house (2 on each floor x 3 floors) indicate they had wood stoves for heat, as these large cooking fireplaces are very poor heaters.

What is above the living room? If you could go straight up with an interior chimney (metal) that would provide the best performance and ease of cleaning. If there is a room above, the chimney pipe would be enclosed in a chase.

There are two stories of bedrooms above, our master bed being right above the living room, and a guest room above that. It would be possible to do an interior chimney pipe and/or chase, but we had sort of set our minds on making use of that fireplace. It's something to consider, though.

 

[begreen]

Yes, I suspected that was a kitchen stove. That is a small room, and you are correct that heat will pocket there without powered assistance. Would an exterior metal chimney be out of the question?

If you go for putting the stove in the cooking fireplace, definitely try the fan trick as shown in the diagram. Your setup should work well with that arrangement. If you find it works well, there are ways of making this into a more permanent and discrete arrangement.

 

[Ashful]

Thanks! I think that's probably the way to go. Good new is that if we're not satisfied with the fireplace install, we can always move it to the living room. Not much is lost.