air intake

[greenkarson]

I've been digging around on here reading about getting the most out of woodstoves.  We burn wood exclusively except when we are away.  I moved our woodstove from our main floor living room to our basement 3 years ago.  And installed  3 floor grates to let the heat rise up from the basement.  In the central floor grate i installed a fan to boost the hot air flow. Our house is not very big its 900 square feet on the main floor and 450 on the second floor.  Its an older house but all well insulated and new fancy window very tight stucco finish no air leaks.  The stove is a large Newmak classic II  with a fire box 24"x12"x16" the 6" flue leaves the top of the stove goes up 24" turns 90 degrees and goes out through the concrete wall and up into the silkirk insulated pipe out side.  The stove should be more then enough to heat our little house.  Yet i can barely get the main floor up to 18degrees Celsius even the basement its self is not all that warm.  I'm burning good dry hardwood. 
 
I've noticed on here that the conversations keep returning to supplying the stove with out side air.  And I'm thinking this may help me so i was wondering because my stove is in the basement could i come in through my basement wall at ground level with a 5" duct and drop 6' and turn it into the bottom intake on my stove?  or would this vertical drop create problems or would this be OK?  and any other suggestions would be greatly appreciated
thanks
karson

[TomW]

Is there a way for cold air to settle back to the basement?

If not, try opening the door to the main house floor.

The cold air has to fall to the lower area to let the hot air rise. I would guess the basement gets plenty toasty?

Simple physics and probably the problem.

Just from here.

Tom

[MattM]

TomW mentions what the HVAC industry calls a 'cold air return'.  You want them to be along the exterior walls so that the cold that comes in goes down to the basement without compromising the warmth of the room.  This is why they typically get located in areas near windows and doors.  I gather you have a stairwell leading down to the basement.  If the stairwell doesn't get overly warm then its more than likely you have a heat escape issue on the upper floor(s).

Your stucco finish on the exterior is a good indication that the type of construction you have.  If the home is more than 50 years old then its probably does not use a continuous siding material and has a lot of air spaces behind the exterior wall.  These air spaces can sometimes be filled from the inside out, but from this chair its difficult to access properly.  The stucco is normally spread out on a lath sub-frame, not the best at keeping outside air out so people generally refit these walls with blow-in cellulose or non-expanding closed foams.  (The latter being better.)  Even if the stucco covers bricks or stone foundation walls, these wall materials are a poor substitute for insulation.  I would suggest you assess the actual insulation in the house using real measurements and eliminate guesswork.  Wood, brick, and block walls make poor insulators.  Today's walls are typically R19 in the temperate climates, even more in a colder climate.  The attic, where you may be losing more heat than the walls, should be at least R38 these days in temperate climates, even more in a colder climate.  HVAC guys in your area may have thermal cameras where they can show you the true leakage going on.

[ghurd]

I do not think it is just the cold air return.

My friend's house was built with 'tin box' around the basement stove to a 3'x3' grate over it.  No cold air return at all.
The basement was in the upper 90sF (35C).  1st floor was mid 60sF (18C).  2nd floor was plain cold.
I pointed out the issues, we cut a few cold air returns in ducts of oportunity, and an hour later it was all fine.

If it was only a cold air return issue the basement would be hot.

The wood is burning and making heat.  The heat is not upstairs, and not downstairs.
It has to be going somewhere.  The only place left for it to be going is outside.
G-

[DanG]

Newmac Classic II? Page five of that stoves "Installation, Operating and Service" states..

REDUCING EXCESSIVE DRAFT: Where permitted by the regulatory authority a hand operated flue pipe key-damper may be installed.

Maybe the stove is acting more like an incinerator than a heat stove?

On outside air intake it notes : For outside combustion air make-up, Newmac recommends that an opening, of 12 sq. inches (78 sq. cm.) free area be
provided to the room in which the heater is installed. If the air is ducted from outside, a 4 inch round duct (to a maximum
of 50 equivalent feet or 15m) should provide sufficient combustion air. If a duct is used, it should terminate at least 1
foot (0.3m) from the appliance and not be directly connected to it.

The manual gives specific reasons an outside air intake may be needed, not enough heat output is not one of them.

Page 17 shows an add-on circulation fan kit that may be what you need...

Edit: added the incinerator comment

[TomW]

Yep, without the flue damper most if not all the heat rockets up the flue.

Another one of those things I would have immediately caught in person.

Ain't remote troubleshooting fun!

Most older homes have plenty of leakage for the combustion air to get pulled in from outside.

It seems the newer super tight super insulated homes require this air.

Much of this stuff is more art than science so it is difficult to see the problem from text on a page and would be trivial in person to understand what is going on.

Tom

[electrondady1]

can you guys explain why the combustion air supply shouldn't be directly connected to the stove?

on my stove there is a 3" dia. tube coming out of the back of the stove where combustion air enters .
there is a metal disk that slides down over the end of this tube and the volume of combustion air is controlled by a lever.
i was thinking of plumbing some  aluminum tubing and elbows (dryer vent stuff) directly on to that opening. and running the other end outside.
i thought i could construct a butterfly valve to control the air intake.

[greenkarson]

Just to recap my first explanation my house is very tight all new windows and doors. and well insulated and vapor bairrer everwhere.  With a open stair well and 3 16"square floor vents  I would think that would be enough air flow both cold return and warm upflow.  And i have a damper in the flue to slow down the heat going out but it seems that it slows down the burn rate but it does'nt seem to effect the amount of heat radiating from the stove. sometimes it seems even with the fire going strong i can  hold my hand on the outside casing on the stove. 
  After reading up on here i have abandoned the flue damper for now. and it seems to work the best without the damper, fire burns a little faster but it throws a little more heat

[12AX7]

A couple of years ago I was looking to purchase a pellet stove.  The dealer was very willing/hot to sell me one.. up until the point where I told him I was going to install it in my basement.  He told me that +70% of the heat would be wasted keeping the basement walls warm,  the salesman talked me out of buying one.  Instead he wanted to sell me a Pellet furnace which would share the same duct work as my gas furnace.   The price of the pellet furnace was 3Xs the cost, and I dropped the idea.

[BrianSmith]

Maybe a lot of that stove heat is going into the basement floor? 

[birdhouse]

i agree about heat being absorbed by your concrete (guessing) foundation.  maybe a layer of foam insulation could help.  also, have you cleaned your pipes lately?  i forget how powerful my stove is after i clean the flue.  it's like it's brand new again.  and not just the pipes, but the stove too including all spaces soot can collect leading to the flue.  i find it very odd, that you can hold your hand on the side of the stove at full tilt.  my morso stove has convection sides.  ie- double walled with gaps at top and bottom to help move air, and i can't hold my hand at full tilt without being burnt badly. 

as far as a sealed home goes, try a blower door test (fairly cheap) to get true results.  very accomplished "green" builders have been humbled by this simple test.  or those heat sensitive cameras are cool too, as they let you know you worst heat leak spots.

i, too am curious as to why a fresh air intake should not be connected directly to a stove.  a direct connection would make the most sense to me.  turn it into a closed system.  no more pulling intake air from all the gaps in a house. 

hope this helps!

adam 

[MattM]

I believe there is a backflow danger from a direct link, the smoke and carbon di-/monoxides can leak into your basement.  This is from the gradient of air pressures in and out of the furnace, your house interior may become the path of least resistance.

[TomW]

Grasping at straws now.

I have had to burn green wood a few times and that made very cool fires because all the energy went into boiling off the water in the wood.

If you were nearby I would pop in and probably have better advice with a quick look.

Burning cordwood ain't rocket science but does need to be done correctly.

Never owned a modern stove and from what I hear most are a PITA to use compared to burning a fire in a steel box, especially if it has a catalytic converter on it.

Is it getting combustion air? Easy way to tell is run it full open awhile then crack the door a bit and if it kicks in burning a lot better with the cracked open door you may have a blockage in the inlet air? You should be able to hear a good fire as it burns wide open on the inlet air.

Best of luck sorting it out.

Tom

[greenkarson]

Thanks everyone for the suggestions. I've burned wood all my life in a bunch of differnt stoves over the years from a antique ornamental stove in my living room that was cast in 1847 to modern day glass fronted airtights with secondary burners.  I'm thinking now that I don't like the design of the stove i have now. While it doesn't have a secondary burner it still seams to be a PITA.  One fact that just popped into my head that i never included before is that this stove has on the air flow control knob a coil spring that a chain hangs from down to the actual air control door that opens and closes to adjust flow.  And as the stove gets hot this spring tightens or loosens allowing the door to close by itself.  and the vent its self is easlly plugged because of its location in the stove.
  And one other thought is that when we bought this stove maybe 6 or 7 years ago it came with a vent that attached directly to the air intake and went straight down.   it was meant for installations in Mobil homes and would go straight out the floor.
  I may haul this stove outside and use it for a shoot'n stove and find a big old steel stove to go down in the basement.  tried and true

thanks karson

[greenkarson]

New developments in this story!!!  after typing my last comments i went down stairs and did a little more studying of the stove.  I opened the ash door in the bottom of the stove and removed the ash pan so i could see the air vent on the side.  With the bottom door still open i lit the fire and watched the spring mechanisim start to move with the heat with in 2 or 3 Min's the vent had closed its self right off.  So that got me thinking again these stoves are promoted as a ten hour burner that's there big sales pitch. And they do this it seems by choking the air almost completely out.  By the looks of it the only air that can get in once it gets hot is what can seep in around the vent door which would be very little.

All this set off another train of thought.  I bought this stove on recommendation by my father.  A long time wood burner himself.  He was telling me about everybody having one of these back in Newfoundland.  And i remember my grandparents on both sides having one in there kitchen and a couple uncles as well.  This may not mean much to you mainlanders.  But this is where it all comes together. Most old houses in the fishing villages never had basements so the stoves would be in the main living area of the house which were normally small houses on one floor usually no more the 800 to 900 square feet. And there is no hardwood for firewood just spruce and fir.   All this equals not needing allot of heat while needing the wood to last as long as possible.  So they would be a ideal stove for there but it seams not for me.  I need a big firebox that can roar wide open when i need it to

Man that's a lot of thinking about a woodstove
thanks karson

[Fused]

Why not remove the spring and make it manual adjustment on the fresh air?

Just an idea. One that a lot of wood burners use.


Fused

[electrondady1]

it seems like a waste to shoot holes in it.
 perhaps you could disengage the thermostatic control and try to control it manually for a bit to see if could still suit your needs.

[greenkarson]

I've been playing with overriding the air intake today.  But its a little warm outside to really put it to the test.

[birdhouse]

a few notes-

karson-  i'd be a little careful with modding the thermal spring.  i used to live with a vermont castings stove with an almost identical mechanism for intake control.  as the stove heated up the air in would slow.  this stove also had a much smaller intake to keep the fire at a reasonable level. anyways, i decided to remove the thermal spring, with manual adjustment, and went to the computer for a while, when i returned, the flue collar and bottom inches of the stove pipe were red/orange.  it was firing very hard.  all i'm saying is these stoves are designed around these thermo control mechanisms.  maybe just try to cut out out a bit out the thermo coil to make it a little less reactive.  you don't want to melt your stove!

tom i don't know if i agree with you about newer wood stoves.  i find them to be great in the fact that they can create much more BTU's from the same amount of fire wood Via. secondary combustion.  with my stove, if i have a good hot coal base, and i throw a piece of really green 1x6 pine in there, immediately the air flow from the above chambers start to emit what looks like 30 little blow torches that has no connection to the flame from the wood.  this is basically igniting smoke, and thus gaining btu's per amount of wood.  this is the easiest way to "see" secondary combustion. 

as far as newer catalytic stoves, i completely agree with you.  though fewer and fewer manufacturers are going catalytic. 

i'm still at a loss about the not connecting a fresh air inlet directly to a stove.  if custom made, with a fiberglass rope gasket, even if the stove did back draft as the fire was out, or almost out, who cares.  no carbon monoxide should get into your home.  if a good sized pipe run is used, i have a hard time believing a newer wood stove could back draft until long after the fire is out, and then is is back drafting? or just moving air about. 

adam

[electrondady1]

i searched this out on the net.
it seems every one agrees that combustion air should be supplied to the stove.
there seems to be two schools of thought whether it is simply made available near the air intake or
it is fitted tightly.
i think i'm coming down on the tightly fitted side.
but what ever method it has to be better than -18c air being sucked into the shop at the entrance door at one end and rolling across the whole shop floor to enter the stove at the other end were the stove is.
the shop is not tight at all so i don't think there is a problem with it being a low pressure zone.
but in a normal house , there are issues if  the stove is in the basement if your house is sealed well and if your chimney is running up the outside of the house.

 

[DanG]

I've seen wind gusts here that got the door and window brass weatherstripping howling like harmonica reeds, as loud as the fire truck sirens are from out in the front yard.. . Unless everything is perfect with multiple back-flow prevention you could have the contents of your firebox evacuated in just a few seconds if the pneudraulic action of winds and wind shadow pulls a vacuum driving a piston of turbulent wedge of compressed air backwards through your air intake system.

[ghurd]

What Dan said.

A long time ago in a galaxy far far away, I was the designated pilot light re-lighter for many many homes.
One in particular comes to mind, a 2 story, with an attic, with the water heater in the basement.  That's a lot of chimney, if that is relevent.
Standard gas water heater with the 1.5" (?) gap between the heater and pipe.
That thing blew out regularly if the wind was strong and from the right direction.
Between the gap, and how the pilot sits in bottom of a water heater, I would almost bet it wouldn't be possible to blow out from wind, but it did.

Always happened at convenient times too, like 2AM Christmas morning.  11:30PM New Years Eve. 11PM the night before deer season. etc.
G-

[electrondady1]

i replaced that old fashioned weather striping years ago with modern foam and rubber gaskets )
but i do   play the harmonica and discovered right away they make a sound whether you suck or blow )

your scenario is dramatic, i appreciate that you are trying to convey to me just how wrong things can go.

i only  lit the stove for the first time on new years day, so i am a rank amateur in wood stove lore.

 if the pressure differential you describe occurred wouldn't the embers, flames, smoke and ash be be contained within the combustion air supply pipe as opposed to being sprayed like a flame thrower around my shop?
or are you suggesting  that such a pressure differential can not  occur if i leave a gap between the stove and the end of the combustion air supply tubing?







 

[DanG]

Having a house structure 'wind shadow' amplify the piddling 2, 3, or 4-inches opening of your air supply line hydraulic multiplication wise is bad mojo. Inserting the air gap is breaking a link in the 'chain' of a vortex that may stretch a hundred feet beyond the exterior opening of your duct. And, no, not having it direct connected is no guarantee you won't get smoke back in the structure when the wind goes wild - but it won't be the 50mph or better fire starter for debris in the duct or lint on the insect screen on the outside vent, or shoveling hot ash out into the yard.

Another example but on a much larger scale - the city sewers. We live on the main canals sixty feet down, wide enough to drive three or four buses side by side through. Vague barometric pressure differentials keep air moving through our sanitary sewer link 24/7/365 - sometimes just creeping and sometimes nearing a leaf-blower exhaust. It's not something I can negotiate, arbitrate or complain about - its always there. I >did< put a 4-inch flap style back flow preventor just before it exits the house to make sure there is never stack gas bubbling into the basement (neighbors arent looking too healthy though). You'd have risks of 'wind gone wrong' going with a direct intake vent unless there were passive dampers built in to the unit and the duct that passed the UL Labs and other safety tests.

[electrondady1]

I've been thinking a lot about this, and had an idea.
but it may be a solution for a problem that does not exist )
by way of a compromise, the cold outside air is ducted to a metal box with no lid.
the combustion air intake is ducted to this same box.
the stove draws air as required at room pressure.
the cold outside air, denser that the warm room air,is contained within the lidless box.

[birdhouse]

this is interesting.  i understand how wind could create a fairly strong negative pressure area on a particular side of a home.  if a directly connected fresh air inlet was located on this side of the home, it could make a stove perform poorly.  could it backflow?  i don't know as i haven't it as of yet. 

i have one of those wind directional caps.  the type that look like a viking helmet.  when the wind gets strong, this type of cap make my stove fire REALLY hard.  i typically choke it down a bit if it's super windy for fear of over firing.  it's almost like the stove's intensity of firing is directly related to wind speed.  this type of set-up would make me think that the pull from a directional cap plus chimney effect would greatly out weigh negative pressure created on a side of a home from wind.  but like i said, i don't know, but wanna try it!

i like the open metal box idea.  in my mind, that would work. 

adam

[97fishmt]

  I had a window sucked out on the leeward side of my cabin a few years ago.
I had to snow shoe in and made it there about midnight and it was quite cold
inside.  After building a fire and turning on the lights and seeing the fog roll
through I discovered I didn't have a window in the dinning room.

  I went out side and the glass was shattered and laying on the outside in the
snow.  The aluminum frame was still attached, the glass was just sucked out.

  I admit the window needed to be replaced but I didn't expect that.  I built my
cabin just from all the stuff I would haul home from work over the years ( I'm a
carpenter by trade) and the windows were free from upgrading homes in the city.

  This windows double pane unit had failed and the outer glass panel was cracked.  I broke the outer glass out so it was only a single pane picture window only held in by the glazing tape.  It was such a weird size I couldn't find one to just swap it out.

  I didn't have any tools to patch the hole in the side of the house that trip other than the chainsaw and a drill.  I cut some plywood and screwed it over the hole that night.

  I found a nice vinyl window about a month later that was an inch smaller in width and height and made it work.  I stays nice and warm inside now.  I can maintain 80 degrees inside when it's 10 degrees outside.

  I think an air supply to the stove is a good idea but I haven't done it yet either.
I do sometimes get smoke into the room even with out a supply.   I'm just very exposed on a hill top.  Sometimes the barometric pressure or a temperature inversion  makes it hard to even get a fire going.

  I've found out with a move of the wood stove that the stove pipe has a lot
to do with the health of you heater.  Straight up is best.  And an insulated pipe
at least on the outside is going to give a better draft.