Deleted

redbuzzard

Deleted_User said:

FreeBear said:

Deleted_User said:

We have a 4 bed bungalow. A new boiler was fitted about 4 years ago - it's 34KW

This year we're (so far, and despite days of freezing weather; -5 last night and STILL not above freezing)  managing to heat the whole house comfortably with a 3kw woodburner.

If I run the woodburner flat out for 13 hours that's 13 x 3kw = 39kw.

A couple of points - Your wood burner may well have a nominal rating of 3KW, but "flat out", I would expect it to be producing quite a bit more heat than just 3KW.

My stove has a nominal output of 6.4KW, but will produce anything between 1.5KW and 9KW when using wood.

Your gas boiler, even although rated at 34KW, is probably not pumping that much out when running the central heating. The amount of heat that can be extracted from your boiler will be limited by the number & sizes of the radiators. If you have a smarter thermostat, it may well be modulating the boiler down to 7KW as the property gets up to temperature.

Fair comment re the woodstove - but for most of the winter it's probably idling at 1kw for most of the day. Although yes - right now it's going full pelt.

We aren't using the gas CH this year. But out of interest (and in case we do things differently in future) can you expand on 'modulating the boiler down to 7kw as the property gets up to temperature'? That just went right over my head!

If you want to know how much your CH is consuming, just read your gas meter.  You can ignore anything used for cooking.

FWIW, I have a 5kW log burner.  The specification says it can produce 2kW-7kW.

[Deleted User]

I know I won't get a reply directly, but maybe someone else can comment - how would central heating need more energy to raise the temperature of the same things by the same amount?

Isn't that claiming that central heating is less efficient than a woodburner?  I find that unlikely, but have admittedly not made any measurements myself.

Mstty

Deleted_User said:

I know I won't get a reply directly, but maybe someone else can comment - how would central heating need more energy to raise the temperature of the same things by the same amount?

Isn't that claiming that central heating is less efficient than a woodburner?  I find that unlikely, but have admittedly not made any measurements myself.

Maybe we can reply to each other.

So a newish boiler(I think this one is 4 years old) could be said to be 90% efficient for these purposes.

Some log burner a can also reach an efficiency of 90%.

Should be a dead heat

[Deleted User]

Mstty said:

Deleted_User said:

I know I won't get a reply directly, but maybe someone else can comment - how would central heating need more energy to raise the temperature of the same things by the same amount?

Isn't that claiming that central heating is less efficient than a woodburner?  I find that unlikely, but have admittedly not made any measurements myself.

Maybe we can reply to each other.

So a newish boiler(I think this one is 4 years old) could be said to be 90% efficient for these purposes.

Some log burner a can also reach an efficiency of 90%.

Should be a dead heat

I'll follow your pun with my own - I'm surprised a log burner wood reach so high.

I would have expected more to be lost in the flue gases.  Perhaps that's the big difference between open fire and purpose-built stove.

Mstty

Deleted_User said:

Mstty said:

Deleted_User said:

I know I won't get a reply directly, but maybe someone else can comment - how would central heating need more energy to raise the temperature of the same things by the same amount?

Isn't that claiming that central heating is less efficient than a woodburner?  I find that unlikely, but have admittedly not made any measurements myself.

Maybe we can reply to each other.

So a newish boiler(I think this one is 4 years old) could be said to be 90% efficient for these purposes.

Some log burner a can also reach an efficiency of 90%.

Should be a dead heat

I'll follow your pun with my own - I'm surprised a log burner wood reach so high.

I would have expected more to be lost in the flue gases.  Perhaps that's the big difference between open fire and purpose-built stove.

This thread really is heating up.

It does appear older Stoves (previous technology and open fires 60-80% efficient) same can be said for older gas boilers so I stick to my original pun.

But don't let me dampen down your flame.

ariarnia

Deleted_User said:

I know I won't get a reply directly, but maybe someone else can comment - how would central heating need more energy to raise the temperature of the same things by the same amount?

Isn't that claiming that central heating is less efficient than a woodburner?  I find that unlikely, but have admittedly not made any measurements myself.

would it make a difference that the boiler is heating cold water but the stove is heating room temp air? 

i've already proved i'n bad at the physics thing but i'm remembering the painful conversation from last week about freezing air or water. 

but i still think the biggest problem is the timescale. if it takes the stove 4 hours to heat the house 2 degrees then i think the better test (if the point is a head to head) is how much gas the boiler uses to maintain that 2 degree increase over 4 hours. 

and obviously we can measure the output of the boiler (with some wiggle for converting from volume to kwh) but can't actually measure the output of the stove in this situation. 

[Deleted User]

ariarnia said:

Deleted_User said:

I know I won't get a reply directly, but maybe someone else can comment - how would central heating need more energy to raise the temperature of the same things by the same amount?

Isn't that claiming that central heating is less efficient than a woodburner?  I find that unlikely, but have admittedly not made any measurements myself.

would it make a difference that the boiler is heating cold water but the stove is heating room temp air? 

i've already proved i'n bad at the physics thing but i'm remembering the painful conversation from last week about freezing air or water. 

but i still think the biggest problem is the timescale. if it takes the stove 4 hours to heat the house 2 degrees then i think the better test (if the point is a head to head) is how much gas the boiler uses to maintain that 2 degree increase over 4 hours. 

and obviously we can measure the output of the boiler (with some wiggle for converting from volume to kwh) but can't actually measure the output of the stove in this situation. 

Yeah, I'm not sure.

The anecdotal evidence is clear - in this situation the woodburner appears to be doing a much better job than the central heating would be.

I just can't work out how to generalise it.

ariarnia

Deleted_User said:

Our wood is mostly free. I don't yet have enough experience to tell you how much wood we're using over a season. So I can't really tell you what it would cost if I had to pay for the wood at current rates. I'm not trying to 'sell' this approach to everyone. It's more about lateral thinking - trying to find better ways of living in the current, energy scarce era. 

we can use between 3 and 4 cubic meters of wood that we use to supplement our heating via gas. i would estemate that would go up to about 5 if we were swapping it round and mostly burning wood with suplementing gas. we (and most other people) can't get that much wood free. we could buy a plot of land but then we also dont realistically have the time to chop and season it (been there and done that growing up). because 'free' wood quite often isnt free if you price up your time and swet. 

i think most people (those that can have wood burners) would be in my camp not yours. so thats really i think the basis i'm at least coming from looking at your hypothetical about if this is a 'realistic' alternative for any significant number of people.

that means having a good idea of how much wood is actually being burnt/how much heat is being given out by the stove to give a decent comparison of costs. and i think for it to work you need a very specific set of curcumstances.

luckily that's you but probably only a tiny number of other people. but its interesting working out how it compares and WHY it works for you. 

Apodemus

Deleted_User said:

ariarnia said:

Deleted_User said:

I know I won't get a reply directly, but maybe someone else can comment - how would central heating need more energy to raise the temperature of the same things by the same amount?

Isn't that claiming that central heating is less efficient than a woodburner?  I find that unlikely, but have admittedly not made any measurements myself.

would it make a difference that the boiler is heating cold water but the stove is heating room temp air? 

i've already proved i'n bad at the physics thing but i'm remembering the painful conversation from last week about freezing air or water. 

but i still think the biggest problem is the timescale. if it takes the stove 4 hours to heat the house 2 degrees then i think the better test (if the point is a head to head) is how much gas the boiler uses to maintain that 2 degree increase over 4 hours. 

and obviously we can measure the output of the boiler (with some wiggle for converting from volume to kwh) but can't actually measure the output of the stove in this situation. 

Yeah, I'm not sure.

The anecdotal evidence is clear - in this situation the woodburner appears to be doing a much better job than the central heating would be.

I just can't work out how to generalise it.

Perhaps I am missing something, but is the answer not simply the total area under the graph of temperature versus time for each of the two scenarios over the chosen time period, divided by the total energy expended?  The units might be a mess (degree/hours per kW?) but we would lose these when we divide Scenario 1 by Scenario 2 to give a simple comparative efficiency?

ariarnia

Deleted_User said:

ariarnia said:

Deleted_User said:

Our wood is mostly free. I don't yet have enough experience to tell you how much wood we're using over a season. So I can't really tell you what it would cost if I had to pay for the wood at current rates. I'm not trying to 'sell' this approach to everyone. It's more about lateral thinking - trying to find better ways of living in the current, energy scarce era. 

we can use between 3 and 4 cubic meters of wood that we use to supplement our heating via gas. i would estemate that would go up to about 5 if we were swapping it round and mostly burning wood with suplementing gas. we (and most other people) can't get that much wood free. we could buy a plot of land but then we also dont realistically have the time to chop and season it (been there and done that growing up). because 'free' wood quite often isnt free if you price up your time and swet. 

i think most people (those that can have wood burners) would be in my camp not yours. so thats really i think the basis i'm at least coming from looking at your hypothetical about if this is a 'realistic' alternative for any significant number of people.

that means having a good idea of how much wood is actually being burnt/how much heat is being given out by the stove to give a decent comparison of costs. and i think for it to work you need a very specific set of curcumstances.

luckily that's you but probably only a tiny number of other people. but its interesting working out how it compares and WHY it works for you. 

It's easy to get data and info about things that everyone does - not least because generally speaking everyone does what the data and info guides them towards.

People that want to try something different need to figure it out for themselves, and bouncing around ideas with others is the best way to do that. Often I get new ideas to try from conversations with others doing things that would never work for me, but something they say gives me an idea that will work in my situation. 

The old ways of doing things aren't working - not just energy prices, but net zero goals. So sooner or later everyone has to find new ways - either that or be stuck with whatever new ways government and industry come up with. Personally, I'm not liking what I'm seeing from them so far so I'm working hard to develop an independent approach!

i get that. really. but i think this links to what i was saying on the vent thread. this is a thread you started but its not a blog about your learning and journey. so people who join the discussion or read it later will take differnt things away from it that are about there situation. and for most people that will include a more direct comparison to the alternative which is gas even at a higher price (or to work out if there better having a stove installed vs having a heat pump etc) 

so for me its about what makes it work for you. and if your point is this is an alternative people should think about. then its about making the info and data available to other who are also trying to figure out something new. and i think that means pinning down some of the things we've been talking about.

 i mean you say your wood is free. but the questions i would ask (and have asked about the wood we can get free and cheap) is if your wood supply can sustainably provide enough wood not this year but for the next 10 (ours can but not ALL we need. we get maybe a cubic meter free and can get another cubic meter ish cheap then pay locally to a farm for the rest at lowish end of market price)?

and what about when you guys get older. if you are processing the wood yourself would you need to switch back to the gas or is it saving you enough that you could afford to pay something towards the wood (or some of the wood) and where's the break even point?

then theres actually knowing your gas system (the stuff about modulation and flow temp plus using trvs to control individual room temp). unless you set your gas up efficiently to give a similar pattern of heat to the fire (giving it 4 hours to heat the house not comparing a blast to a slow heat) then other than the wood being free how do you know which is actually using the most energy?

that might not be relevant for you given your free wood but that's what other people would need to learn from the thread to work out the relative costs for them. and yes they can do it for themselves but then this is a less helpful thread for people trying to work out there own way if you see what i mean?