Jotul 3CB takes a long time to warm up my small house

[steveh2112]

it takes at least a couple of hours of full firebox to get my 3CB up to the point where it heats a small space, about 300sqft. is this normal? i have a double wall flue pipe and i feel most of the heat is going straight out the chimney. the 3CB doesn't have an outside air option so i suspect its taking the warm air from the room out of the chimney.

i'm still renovating my house so its not a 100% sealed up at the moment but its not too bad. any tricks to make it feel warmer quicker?

thanks

 

[EbS-P]

how many degrees is it raising the temperature? What is the moisture content of your wood?

Blankets over windows and doorways.

 

[begreen]

Yes, it sounds like there is significant heat loss or the wood may not be fully seasoned.
What is the stove top temperature? What temperature was the house before the fire was started?
Is this small space a room in a larger house?

 

[steveh2112]

its not real cold right now, maybe 40-50 out at night. wood is 12% moisture. its a 800sqft house but only heating living room and bedroom, about 1/2 of the house

 

[begreen]

What is the interior temp before the stove has started? What temperature is the stove top?

 

[steveh2112]

not sure, i'll check this evening, thx

 

[stoveliker]

12 percent is unlikely. (Almost impossible unless in a dry desert climate.)
One needs to know the internal moisture content. It dried from the outside inward so the outside is the driest. I suspect that is what you measured.

Bring a split in the home for 24 hrs, then resplit, and then push the pins as deep as possible and parallel to the grain innthr freshly exposed surface.

Also,. have you done the dollar bill test of the door seals? A leak would result in much more heat going up the flue.

 

[steveh2112]

my moisture meter says 6 to 10% actually

 

[stoveliker]

Then something is wrong. The equilibrium moisture content of wood in your climate can't get that low.

 

[begreen]

my moisture meter says 6 to 10% actually

That is fully-dried, lumber moisture content. If the measurement was taken after splitting the wood in half and tested on the freshly exposed, middle of the wood, then the meter is possibly faulty.

 

[steveh2112]

its been running for a couple of hours and averaging about 330 to 380 measured on top of the stove a couple of inches from the flue pipe.

BTW, the moisture meter is brand new. i have no idea how accurate it is but the wood feels very dry. i have to cut it because 16" logs don't fit in the tiny 3CB, and when i run my dewalt chain saw through it, it seems really dry

 

[stoveliker]

https://www.fpl.fs.usda.gov/documnts/fplrn/fplrn268.pdf

12% is possible, but highly unlikely. (I have not seen wood (even pine) at 12% even after three years in sun and under a roof with zero rain hitting it - 14% is my lowest observation.)

Are your pins all the way in? And are you measuring with the "pin holes" poking into the same fiber, i.e. as in this orientation? (and *not* as shallow as this, as the pins in this pic don't make enough contact with the wood, leading to a higher resistance and thus incorrectly lower displayed moisture content)

Barring a measurement that makes sense, what is the history of your wood? I.e. when bought, and what happened between the delivery and now? (How was it stored.)
Or when did you cut, split, and stack it? (How was it stacked?)
What species of wood?

The reason why we ask is because if wood is too wet (and so far we don't know that that is not the case), you'll be using a large part of the heat to boil away the water in the wood. A split of 5 lbs at 20 % still has a full pound of water that needs to be boiled into vapor that can exit the flue. ALl the heat needed for that is not coming into your room. (And the fire will be cooler, and thus dirtier.)

Can you burn with the primary air mostly (and, of course, the start up air completely) closed without the fire choking to smoke only, or do you have to run fully open?

 

[begreen]

its been running for a couple of hours and averaging about 330 to 380 measured on top of the stove a couple of inches from the flue pipe.

BTW, the moisture meter is brand new. i have no idea how accurate it is but the wood feels very dry. i have to cut it because 16" logs don't fit in the tiny 3CB, and when i run my dewalt chain saw through it, it seems really dry

The stove top temp is low. I had this stove and ran it with a stovetop temp between 500 and 650º regularly. That's a large difference in heat output.

When you measure the wood moisture are you resplitting the wood, then testing in the middle of the freshly exposed face of wood?

Once the fire is burning well is the startup air intake close and are you turning down the air to encourage good secondary combustion?

 

[steveh2112]

i guess my meter is bad, when i measure the moisture between my 2 fingers i get 13%, i'm guessing that's way too low given that humans are mostly water. i got the meter a few months ago on amazon, too late to replace it now i think but i'll try.

i am measuring the wood as it come straight off the pile. i bought it already seasoned. i will try split it and measure.

when i close the main air intake down to about half it slows but burns ok, when i shut it off it pretty much kills the fire. no smoke in either case so i guess that's working ok.

i usually run it with primary air full open (start air closed of course). should i be running primary on half do you think?

BTW, i just cut a log in half and tested the end grain and got 13%

 

[stoveliker]

In most cases buying seasoned wood is not dry enough. Sellers have it in a large pile on the ground, both of which are very detrimental to it drying.
Best is to buy wood, stack it off the ground for two years, preferably top covered. That's a large investment up front but it allows drying and you only have to buy to replenish the yearly usage after that.

No (secondary) flame at the top of the firebox with the primary air closed indeed suggests wood that's too wet. (Btw, measuring in the end grain (i.e. the cut end) is not the right way. The orientation of the wood fiber matters; the meter is calibrated to convert the electric resistance into a moisture content only for the way of measuring I described above.)

Before buying a new one, do it as above, and see what it measures.

Yes, these stoves provide more heat with the primary air (nearly) closed.

 

[Todd]

If you’re burning mostly wide open you’re sending most of the heat up the flue. Start out with high air til the load gets flaming good then bring the air down in a couple increments like Med then Med low. The whole process could take about 15-20 minutes. A flue thermometer is a great tool to guide you through this and also tells you how much heat is going up the chimney.

 

[steveh2112]

ok i split one of my bigger logs and tested along the grain and get 15%

its warmed up a bit here in upstate NY so not sure i need the fire tonight but next time i'll try with lower main air next time

i have a flue thermometer but on a double wall flue it doesn't do anything. i moved it to the stove where it actually provides some info

i'm hoping house warming season is done soon so hopefully next year the half FC i have now will be bone dry. i'm splitting some felled trees from my garden today, i cut them about 12" long and split quite small so hoping will dry out good enough for next season if i keep them dry.

BTW, i got a $300 electric log splitter from amazon and the thing is a monster, its plowing through 20" rounds like a knife through butter

 

[begreen]

BTW, i just cut a log in half and tested the end grain and got 13%

You are doing this wrong. Never test the end grain of wood for moisture content. That is a meaningless reading. Wood dries from the outside in. In order to get an accurate reading one must first split the wood in half. Then test in the middle of the freshly exposed face of wood. For the most accurate reading, the wood should be around 72º before splitting.

 

[stoveliker]

You are correct about the flue thermometer. For double walled you need a flue probe. Condar sells them; same reading front but a metal rod that has to go into the flue. I.e. you have to drill a hole.

 

[steveh2112]

i tried my stove last night with more wood and the primary air about 1/2 open and definitely better, average about 400. it was a warmer evening than usual however so i'm sure that helped made it feel warmer too.

 

[begreen]

400º is still cool for this stove. Next load, add some dry 2x4 cutoffs to the firebox.