Deleted

[Deleted User]

By only doing short spells are you not using the boiler at its worst?

It's like (well not really at all like but I can't think of a better analogy) including the time and power output of loading the wood and finding the matches in the calculation of woodburner output.

It seems like your existing setup works very well for you - I'm jealous.

drsquirrel

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.

But it's not running flat out - sometimes is spends a few hours damped down and burning slowly. Every so often I'll put a home made paper brick on it and leave it for an hour - so that it almost drops out of the green zone - before stoking it up again. 

The point is, and I don't really know what to make of it yet, my woodburner is running all day using less energy than my boiler would use in an hour.

The pattern of heating is different - more really cosy rooms with the woodburner, but more cooler areas in the house too. We definitely get up to colder rooms, but they quickly get EXTREMLY cosy. Swings and roundabouts - both work well...I prefer the woodburner. 

This isn't about cost as I get most of my wood for free. But I'm just trying to get my head around all the factors involved in switching to a more energy efficient way of running the house.

It is possible the wood stove can put out more than 3kw of heat, that figure is nominal.

Consider where it is drawing the air in from, do you have a dedicated air feed? If not the air is being dragged into the room via gaps around the house.

InvertedVee

Deleted_User said:

M0KBJ said:

@Deleted_User Wow, 14.6kW for an hour is certainly a blast!

Is that higher than you expected? 

I deliberately switched it on when the house was at it's coldest to make sure it was having to work hard.

Question is - if I had a smaller boiler (or throttled this one in some way) would it be more efficient? As things stood - it only managed to increase temps by 2 degrees (roughly) across the whole house. A smaller boiler might cost less to run for an hour but presumably it would be even slower to warm the house from cold?

If anyone has any other tests to suggest I plan on experimenting with SHORT spells of running the boiler (not willing to see how long / how much it takes for CH to get the whole house up to 20 degrees!! LOL). Might as well do tests during the cold spell to help keep the fabric of the house warm.

I wouldn't want to suggest you're doing anything wrong. You just have a different approach to me and it seems to suit you well for your situation.

You asked about restricting the boiler output. Boilers are generally sized to give the predicted hot water demand. Running the boiler at low output over a long period is the most efficient way to use it in a well-insulated home. I referred to the Worcester Bosch installers' manual to limit mine from the default 24kW max central heating output to 7kW and I use a 48C flow temperature. It's raises the temperature of the house very slowly. (When I go away, I let the house fall to around 12C and with these settings it takes up to 24 hours to get it thoroughly warm again in winter. I can set my thermostat from my phone while I'm away, which helps).

Normally, I set my thermostat to 19C in the day and 17.5C overnight. This means my boiler purrs along very gently and efficiently from 6am to midnight, with an output of an average 2kW. My approach might be ineffective for your home/location/lifestyle but it suits me perfectly.

HeatGeek has some good consumer info on all this, aimed at consumers: https://www.heatgeek.com/should-your-heating-be-left-on-all-the-time-or-not/

InvertedVee

Deleted_User said:

So when the logburner is my workhorse (it has to be - wood is free) the only sensible way to use CH to supplement is (correct me if you think I'm wrong) a short, sharp burst?

Sorry, I can't really guess what might be right for your situation. And even though our boilers are very similar, there are lots of complicating factors such as the rate of heat loss from the home, the radiator positions and sizing, the kind of thermostat you're using etc.

But if you're interested in an experiment you could live for a week in winter with something like:

• Boiler flow temperature set to 50C
• Gas CH programmer set to 19C from, say 6am to 5pm, then 17.5C until the next morning.
• Wood-burning stove lit from 5 or 6pm to 10pm.

Ignore the gas consumption figures for the first couple of days, which are bound to be high as the fabric of your home becomes thoroughly warm and dry.

But I can see that all your freely available wood and the cosiness of a real fire is very appealing!

ariarnia

Deleted_User said:

1 hour later the hall temp is 11.5 degrees and having checked various other rooms I'd say that it boosted the whole house by aprox 2 degrees. I took a quick look at the boiler display (haven't looked at the manuals yet) and it said 'eco' and 64 degrees (no idea yet what that means).. 

id recommend also checking the rads are getting good and hot in that time. if you arent using it often ad its going from stone cold to hot when you do use it then thats a recipie for air pockets. a radiator key is a couple of quid and just make sure you have a flannel or something for when the air/water starts to spit. 

Effician

Deleted_User said:

drsquirrel 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.

But it's not running flat out - sometimes is spends a few hours damped down and burning slowly. Every so often I'll put a home made paper brick on it and leave it for an hour - so that it almost drops out of the green zone - before stoking it up again. 

The point is, and I don't really know what to make of it yet, my woodburner is running all day using less energy than my boiler would use in an hour.

The pattern of heating is different - more really cosy rooms with the woodburner, but more cooler areas in the house too. We definitely get up to colder rooms, but they quickly get EXTREMLY cosy. Swings and roundabouts - both work well...I prefer the woodburner. 

This isn't about cost as I get most of my wood for free. But I'm just trying to get my head around all the factors involved in switching to a more energy efficient way of running the house.

It is possible the wood stove can put out more than 3kw of heat, that figure is nominal.

Consider where it is drawing the air in from, do you have a dedicated air feed? If not the air is being dragged into the room via gaps around the house.

There is no dedicated air feed (and it's not something we'd consider changing regardless of potential benefits because of the hassle) but I think it's better this way. We can boil water on the stove all day, dry the washing and the whole house is kept nice and dry. So it's sucking cold, damp air from all over the house.

We have direct air feed on our stove & to dehumidify the house we let the warm damp air out through the highest window in the house whilst dragging cold dry air in from the lowest window opening in the house, 10 mins is normally plenty otherwise the air can get too dry.

Even on cold misty days the windows get opened as the relative humidity will plummet once the incoming air is warmed.

Qyburn

M0KBJ said:

@Deleted_User Wow, 14.6kW for an hour is certainly a blast!

If the boiler's rated at 30kW, that's only a 50% duty cycle, not that surprising starting from cold. In fact it suggests the radiators or circulation are the limiting factor rather than boiler output.

Qyburn

drsquirrel said:

It is possible the wood stove can put out more than 3kw of heat, that figure is nominal.

The standard for rating used to limit how frequently the stove was refuelled.  For example out Rayburn was 35,000BTU rating with four hour fuelling cycle as the standard at that time specified. Actual maximum output was 55,000.

Qyburn

Deleted_User said:

So when the logburner is my workhorse (it has to be - wood is free) the only sensible way to use CH to supplement is (correct me if you think I'm wrong) a short, sharp burst?

I don't know what sort of controls you have but I would think it should be possible to set thermostats and TRVs so that when the woodburner gets into its stride the CH progressively shuts off. You'd need the thermostat somewhere regularly occupied but least affected by the woodburner, and at a relatively low temperature.

So the CH only supplements the heating until the stove's fully operational, or if for some reason you can't run the stove.

BUFF

M0KBJ said:

Deleted_User said: ...I took a quick look at the boiler display (haven't looked at the manuals yet) and it said 'eco' and 64 degrees (no idea yet what that means).

64C is your boiler flow temperature. It's set well outside the range for efficiency and it won't be running in condensing mode. But if you're going down the short hot blast route I guess you don't have much choice but to set it so high.

At 64C flow his boiler should be condensing (return needs to be under ~56C) but certainly if it can be tweaked down to 55C or even lower then efficiency should improve.
He whould be aware that dropping the flow temperature may/will increase how long it takes for the system to raise the house temperature by the same amount under the same climactic conditions.

If the op has TRVs what were they set at? Obviously can't expect the system to raise room temps above that at which TRVs are set to close.