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1186 posts

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DR

  #2496991 2-Jun-2020 19:18
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benokobi:

 

Pellets are just compressed waste wood, schools are replacing their coal boilers with pellet boilers as they burn super clean.

 

 

 

 

Which is part of my query.  Why burn briquettes or bagged kiln dried log wood when pellets can be burned in the wood stove, and they burn hotter and cleaner.  And apparently even cheaper!


276 posts

Ultimate Geek


  #2497047 2-Jun-2020 20:44
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gchiu:

 

Ge0rge:

We grow our own trees to replace the ones we cut down for wood each year, so for us the time is the only cost, plus petrol for the saws and splitter. We're on slightly over an acre.

We turn our hot water cylinder off once it gets cold enough to need the fire on - the wet back means no water heating bill for winter. We also cook stews, soup and sauces on the fire when it's going, and a fiar bit of that is bottled and lasts for a year or two. We also do preserves on the fire too.

Has anyone got a recipe for heat-pump plum sauce?

 

 

 

With the Covid-19 people are reassessing their lifestyles.  Looks like you're there already.

 

BTW, is an acre enough to grow enough trees to replace the ones you burn in winter?

 

Has anyone got a recipe for heat-pump baked potatoes? 

 

 

You might be struggling on an acre if you want space for much else. I have a line of about 60 or 70m of gums beside a creek. I take down one or two trees a year for firewood. They are the copicing type which just regrow from the trunks.

 

 

 

 


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  #2497087 2-Jun-2020 22:13
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Pretty much all wood's (incl the likes of pallets which are compressed sawdust) sit at around 15 and 20 MJ/kg

 

https://cfnielsen.com/faq/calorific-values-for-different-raw-materials/

 

It doesn't really matter if it is hard or soft, Hardwood simple fits more weight (and energy) in less space.

 

If we run with say 17.5MJ/kg, that works out to 4.86 MJ/kWh. Burnt at 70% efficiency, thats 3.4kWh/kg of usable heat.

 

Using the 20kg firetime pellet bag cost from OP (66c/kg), this works out to 19c/kWh of usable heat.

 

The other option listed by OP work out to 30c/kWh for Briquettes and even more than that for the dry round wood.

 

 

 

Regarding the bulk wood, Macrocapa's density is 485kg/m^3. If we assume a thrown cube is half air and half wood, that means the 3 cubes that OP purchased for $400 weighs about 730kg.

 

3.4*730 = 2,474kWh. This works out to 16.1c/kWh.

 

 

 

Given the marginal cost of power at my place is 15.7c/kWh (incl GST), none of the above options make financial sense for me. I can run a cheap resistance heater for roughly the same price as the bulk wood, or run my heatpump at roughly 1/3 of that cost. All without the the effort & time associated with wood handling, storage, fire lighting, chimney sweeping etc.

 

In my mind using wood for heating is only a cost effective solution if you have access to wood for free, and only if you consider the time spent gathering, chopping etc to be recreational. (Plus people who are off grid or who have very expensive power)

 

With that in mind those buying wood to burn are unlikely to be doing it for financial reasons. Likely aesthetics is a key driver (fires do look great). Such buyers may prefer the aesthetics of logs rather than pallets.

 

Logs & Briquettes from hardware stores and supermarkets are very expensive. My assumption is that they are only purchased by people who only use the fire on special occasions (I.e. gathering at the house), or those who have been caught short with their wood supply and want something to bridge the gap until their next bulk wood delivery arrives in two days time...

 

I guess the wood pellet marketplace is a lot more competitive as people with pellet fires will buy a lot of them and hence shop around.


276 posts

Ultimate Geek


  #2497169 3-Jun-2020 06:35
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One good thing for fires is they help reduce the peak load on the electricity system. Also for many poorly insulated homes they can make them comfortable easily. There’s no comparison with the output of a small wood burner compared to the largest domestic heat pump.

 

The affect on health from particulates is the big issue esp in the urban context.


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  #2497207 3-Jun-2020 08:56
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@Scott3 I would say a thrown cube is more like 1/3 air 2/3 wood. 2m^3 dry Macrocarpa thrown on to my trailer is around 600 - 650kg not including the trailer.




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  #2497213 3-Jun-2020 09:20
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Some other things:

 

An efficient wood burner might be 70% efficient, and get 3.4kWh/kg of heat, but some of that heat is used to drive the draught and that goes up the chimney as lost heat.

 

Some wood can be free - heat treated pallets are left lying around the city to be picked up and used as firewood.  Some people do this and on sell it as firewood after cutting and bagging it.

 

The ashes are a source of potash for the vegetable garden, and a wood burner is also useful on the rare instance of a power blackout.

 

But the main issue is PM2.5, and its environmental effect both inside and outside the house.  Wikipedia says black carbon can persist for 100 years in the atmosphere.


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Master Geek


  #2497284 3-Jun-2020 10:55
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An interesting topic.

 

I have recently moved from a well insulated doubled glazed home with a gas fired radiator heating system. This was a brilliant system especially when we had gas capped at $129 month with Genesis (they stopped this plan last year).

 

Our new house is in a semi rural location with a wood burner with wetback heating a hydroponic floor as its only heating source. The previous owners used to cut their own wood (not on the property) and used about 3 or 4 cords a year.

 

At around $380 a cord split and delivered that's around $1000 - $1200 a year for heating alone. 

 

Is it even possible to burn briquettes or pellets in a regular wood burner? I've not seen this done.

 

I think solar will be our next move.





Life is a daring adventure or nothing at all...


308 posts

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  #2497307 3-Jun-2020 11:54
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bluedisk:

 

Is it even possible to burn briquettes or pellets in a regular wood burner? I've not seen this done.

 

 

Pellets are meant to be burned in a specific pellet burner. However you can get a pellet tray or a pellet basket that lets you use them in a standard wood burner - Azwood (who makes pellets) used to sell one but I can't say I've seen them around recently.





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Geek


  #2497326 3-Jun-2020 12:51
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My place has a pellet burner installed by the previous owner. Even though it is cleaner and supposed to be efficient, I would not recommend it at all

It's noisy due to the fan running to spread the heat, the constant machine noise to feed the pellets every 2-3 seconds, and of course it requires electricity to even get started which we all know NZ is still suffering power outages every single winter due to the windy/rainy weather with the overhead power lines...

And a bag of pellets is just....Not lasting at all.



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  #2497330 3-Jun-2020 13:02
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antonknee:

 

Pellets are meant to be burned in a specific pellet burner. However you can get a pellet tray or a pellet basket that lets you use them in a standard wood burner - Azwood (who makes pellets) used to sell one but I can't say I've seen them around recently.

 

 

 

 

You can see their page on the wayback machine  but I don't think they advertise it anymore on their site.

 

I normally add pellets to an existing hot fire as they can be hard to burn by themselves.  Just wrap them up on some newspaper to make a log.  But with dwindling sources of newspaper I may have to get myself a pellet tray.




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  #2497332 3-Jun-2020 13:08
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bluedisk:

 

At around $380 a cord split and delivered that's around $1000 - $1200 a year for heating alone. 

 

Is it even possible to burn briquettes or pellets in a regular wood burner? I've not seen this done.

 

I think solar will be our next move.

 

 

 

 

I am consoled by the winter energy payment which is about $600 I think.

 

Solar using PV panels are likely to be too expensive to achieve the same amount of heating.  Solar works best on a highly insulated home.

 

You don't get 14kWh on a winter's day to fill up a Tesla battery with 3-5 kW of panels which is then only going to get your 2kW heater going only for less than a third of the day.  But you have slab heating and water heating.




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  #2497335 3-Jun-2020 13:10
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kipkip: 

And a bag of pellets is just....Not lasting at all.

 

How long does a 20kg bag last?  What's the kW rating of the heater?


276 posts

Ultimate Geek


  #2497375 3-Jun-2020 14:01
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gchiu:

 

bluedisk:

 

At around $380 a cord split and delivered that's around $1000 - $1200 a year for heating alone. 

 

Is it even possible to burn briquettes or pellets in a regular wood burner? I've not seen this done.

 

I think solar will be our next move.

 

 

 

 

I am consoled by the winter energy payment which is about $600 I think.

 

Solar using PV panels are likely to be too expensive to achieve the same amount of heating.  Solar works best on a highly insulated home.

 

You don't get 14kWh on a winter's day to fill up a Tesla battery with 3-5 kW of panels which is then only going to get your 2kW heater going only for less than a third of the day.  But you have slab heating and water heating.

 

 

The answer, in my view, is we should be moving to zero energy/passive house construction for new housing, given that the technology is reasonably mature and if we are serious about global warming...just straying completely off topic.


33 posts

Geek


  #2497383 3-Jun-2020 14:08
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gchiu:

kipkip: 

And a bag of pellets is just....Not lasting at all.


How long does a 20kg bag last?  What's the kW rating of the heater?




A 15kg bag can last for 15-20 hours of burning. Not sure about the rating but it was an insert to an open fireplace for a ~16 square metres enclosed living area.

FPR

147 posts

Master Geek


  #2499670 6-Jun-2020 14:48
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gchiu:

 

antonknee:

 

Pellets are meant to be burned in a specific pellet burner. However you can get a pellet tray or a pellet basket that lets you use them in a standard wood burner - Azwood (who makes pellets) used to sell one but I can't say I've seen them around recently.

 

 

 

 

You can see their page on the wayback machine  but I don't think they advertise it anymore on their site.

 

I normally add pellets to an existing hot fire as they can be hard to burn by themselves.  Just wrap them up on some newspaper to make a log.  But with dwindling sources of newspaper I may have to get myself a pellet tray.

 

 

 

 

 

 

Why do you wrap them up in some news paper to make a log and not just throw a small coal shovel load in the burner.


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