placing chimney pipe in masonry chimney

[jonasp]

Hi,

So i'm trying to figure out what my best option would be to place a chimney pipe inside a masonry chimney.
The masonry chimney is 200mm but for a new rocket mass heater I would at least need a 180mm pipe.
Unfortunately I can't fit a insulated pipe in there.

What's the best course of action to insulate the 180mm pipe inside the masonry chimney?

[fuegos]

Hello and welcome to the forum.Working on old stone houses in Wales some years ago we used to break holes in the chimney & insert ceramic liners, mostly to stop leaks and reduce the sometimes large diameter to give more draw.We would fill the gap with a perlite mortar.

[jonasp]

Thanks, so much valuable information on this forum!
Sounds like a lot of work. The chimney doesn't have any leaks (as far as i'm aware of) and is pretty straight.
In my inexperienced opinion running a 180mm pipe through it seemed like a good and easy solution. I was thinking filling up the empty space with perlite for insulation.
would this be a viable solution?

[Vortex]

I was going to suggest that but with a 180mm pipe in 200mm chimney your only going to have 10mm gap around the pipe. It would be difficult to properly fill such a small gap with perlite or vermiculite. Do you really need a 180mm system?

[jonasp]

Nov 15, 2022 9:30:44 GMT -8 Vortex said:

I was going to suggest that but with a 180mm pipe in 200mm chimney your only going to have 10mm gap around the pipe. It would be difficult to properly fill such a small gap with perlite or vermiculite. Do you really need a 180mm system?

I think a 180mm system would be perfect for my space. I calculated 4.8 kW for the colder days (probably a bit more than that even)
In a year or 2 the house should be better insulated and would probably only need around 3 kW or less.

The house is also build with expanded clay bricks so the chimney already has a bit of insulation, not sure if that will make a difference.
The first 2 meters off the chimney would be properly insulated and then roughly 6meters in the chimney.

Would the not perfectly insulated parts cause that much difference?

[Vortex]

I'm not much good on the math side of it, but I remember 4-6KW being the rated output of a small wood burning stove, which are usually 5"/125mm system size, so it sounds to me like a 150mm system would be fine for you, then you'd have 1"/25mm gap all around the pipe to fill with perlite. Use the straight rigid stainless as well, not flexipipe.

[fiedia]

The first 2 meters off the chimney would be properly insulated and then roughly 6meters in the chimney here

I see some possible issues. If you insulate just the bottom of your flue, hot fumes coming from your stove will do it fine in the lower part of the chimney but will get cold in the upper part. It may produce condensates which will run down the inner flue walls. Best case, you get some dirty stinking liquid dropping down from your chimney, worst case this liquid accumulates inside the perlite and burst into flame one day if it gets too hot.

In a year or 2 the house should be better insulated and would probably only need around 3 kW or less.

Could you warm your house with just a cheap electrical radiator ? I built a 5" batch rocket (3 to 4 kW). It was not big enough to heat a 35 m2 room (I admit the insulation is very bad). I do not know much about your house insulation and volume, may be you can rely on the power you need to heat your house presently.

 

[jonasp]

Nov 16, 2022 7:24:23 GMT -8 fiedia said:

The first 2 meters off the chimney would be properly insulated and then roughly 6meters in the chimney here

I see some possible issues. If you insulate just the bottom of your flue, hot fumes coming from your stove will do it fine in the lower part of the chimney but will get cold in the upper part. It may produce condensates which will run down the inner flue walls. Best case, you get some dirty stinking liquid dropping down from your chimney, worst case this liquid accumulates inside the perlite and burst into flame one day if it gets too hot.

In a year or 2 the house should be better insulated and would probably only need around 3 kW or less.

Could you warm your house with just a cheap electrical radiator ? I built a 5" batch rocket (3 to 4 kW). It was not big enough to heat a 35 m2 room (I admit the insulation is very bad). I do not know much about your house insulation and volume, may be you can rely on the power you need to heat your house presently.

 

That sounds like a situation I want to avoid, thanks for the input!

At the moment i'm warming my house with gas boiler but it's hard to heat up the house at colder temps and gas prices are so high... We really like the look and feel of a mass heater so the conclusion to make a mass heater was a no brainer. Electrical radiator uses too much electricity imo..

[jonasp]

Nov 16, 2022 2:34:23 GMT -8 Vortex said:

I'm not much good on the math side of it, but I remember 4-6KW being the rated output of a small wood burning stove, which are usually 5"/125mm system size, so it sounds to me like a 150mm system would be fine for you, then you'd have 1"/25mm gap all around the pipe to fill with perlite. Use the straight rigid stainless as well, not flexipipe.

I've taken a view steps back to recheck what I would need.

The information found on batchrocket website suggests it's better to go bigger rather than smaller.
If I trust my estimates of kW I need to warm up the house, a 150mm system wouldn't be enough assuming I would fire it twice a day.

(figures from batchrocket.eu 2 fire a day)
150 mm -- 6,0 kg -- 1,9 kW 
175 mm -- 9,5 kg -- 2,9 kW

I don't have any experience with this so please correct me if i'm wrong or overseeing things.

[fiedia]

According to my measurements on a 125mm batch rocket, you may get 30% more heat than your estimates. I measured that my bell radiated 3 to 4 kW with 4 burns a day. Heat radiating from the firebox was not measured.

Is there a tag on your gas boiler which could give some information (power, part number...) ? 

[jonasp]

Nov 17, 2022 0:12:08 GMT -8 fiedia said:

According to my measurements on a 125mm batch rocket, you may get 30% more heat than your estimates. I measured that my bell radiated 3 to 4 kW with 4 burns a day. Heat radiating from the firebox was not measured.

Is there a tag on your gas boiler which could give some information (power, part number...) ? 

Oh looks like the chart I'm following is not correct or I'm misinterpreting it. According to the chart you would get 2.2 kW from a 125mm system when fired 4 times...

The nominal output of the gas boiler is 21kW but I can't rely on that number at all..

The space I want to heat is roughly 80m2. Mostly insulated, double glass (not HR), heatloss to other rooms which 1 is poorly insulated...
I would roughly at the moment need 4-5kW to heat it up when properly insulated more like 3kW

Even with an increase of 30% a 150mm system would give 2,5 kW at 2 fires a day so I'm still considering a 180mm system even though the chimney is still a problem to solve.

[Vortex]

I have a 40m2 cabin with fairly poor insulation- 1" in the roof, 2" in the walls, 4" under floor. My 6" Vortex stove is total overkill for it, live with the door open most of the time in the winter, and that's just one 3/4 load a day, it's quite mild where I live though, where are you?

[jonasp]

Nov 17, 2022 5:32:49 GMT -8 Vortex said:

I have a 40m2 cabin with fairly poor insulation- 1" in the roof, 2" in the walls, 4" under floor. My 6" Vortex stove is total overkill for it, live with the door open most of the time in the winter, and that's just one 3/4 load a day, it's quite mild where I live though, where are you?

Oh wow I guess I'm underestimating the power of rmh (or in your case the beautiful vortex stove, I would stare into that double vortex until the fire dies).
I live in Belgium so not that bad but in the winter it can get around 0 Celsius, average temperature in the winter months is probably 3-4 Celsius.

[fiedia]

The nominal output of the gas boiler is 21kW but I can't rely on that number at all

Now you have to estimate how often the gas is burning when it gets really cold, 4 hours a day? 6 hours?

Is your boiler also providing hot water?

[jonasp]

Nov 17, 2022 8:09:39 GMT -8 fiedia said:

The nominal output of the gas boiler is 21kW but I can't rely on that number at all

Now you have to estimate how often the gas is burning when it gets really cold, 4 hours a day? 6 hours?

Is your boiler also providing hot water?

It's hard to calculate that I'm running in the space 1 wall radiator and the rest of the heating is done by floor.
I'm quite convinced the setup is not optimal, loss on heating pipes and water distribution (65 vs 40Celsius circuits). The gas boiler does not provide hot water.

Unfortunately it's a older gas boiler so no way to check how many hours it's running a day, unless I stand next to it a whole day.