Performance and power of a wood stove, definitions?

[Christophe]

I've been wondering how the power is defined for a while and on the other hand the yield (the 2 varying "together") of a wood stove but also of a wood-burning boiler ...

Under the woodburning file that I am doing (which I would like as complete as possible), I would like to clarify this point!

Because as much on gas or oil is easy (= fuel flow), as much in wood heating, it is difficult to give a power ... except maybe in pellet or wafer heating where we also have a " fuel flow "which can give an idea of ​​the power ...

But in the case of logs or briquettes? Is there a standard? A law ? Or does each manufacturer give power as it sees fit? In this case according to what definition?

Here are the powers that can be used in the case of a wood-burning appliance:

- maximum power (peak)
- average power over X h
- average power of a complete cycle = PCI of loaded wood / burning time
- instantaneous power reached Y h after starting
- ....etc., etc...

Same thing for the yield: this depends mainly on the instantaneous power, so as it is defined in the commercial docs? This is obviously a "maximum" performance ok but under what conditions ...

[Christophe]

A first response element (this is the first time I see it) on the Deville site, they give: nominal power and maximum power for each device.

Examples: http://www.deville.fr/prdt.php?c=21&s=99&p=25

Features
• Nominal power: 9 kW
• Maximum power: 22,5 kW

It remains to be seen how this nominal power is defined ...

[Did67]

AFNOR sells (very expensive; around a hundred euros) the standards in question. The answer is undoubtedly in there!

To give you at least one idea (for free), I am going to go dig in the German / Austrian homes. In general, their test protocols are available online and free of charge.

I would like to take this opportunity to remind you that if the Flamme Verte label is decisive for the tax credit, it is only an A MINIMA standard. And not a "distinction", as this is somewhat presented and implied by the manufacturers.

Elsewhere, this standard makes people laugh so much that it is undemanding.

(for tax reasons, it is of course necessary to disseminate the information; but to insist that it is not at all glorious as a performance!)

[Christophe]

To give you at least one idea (for free), I am going to go dig in the German / Austrian homes. In general, their test protocols are available online and free of charge.

Thank you! On my side I found this: https://www.econologie.com/normes-et-reg ... -4225.html

It sums up well the legal framework of wood heating, I think everything is said but ... there are no details ... figures!

I would like to take this opportunity to remind you that if the Flamme Verte label is decisive for the tax credit, it is only an A MINIMA standard. And not a "distinction", as this is somewhat presented and implied by the manufacturers.

I just spoke about it in a specific subject: https://www.econologie.com/forums/label-flam ... t9210.html

Elsewhere, this standard makes people laugh so much that it is undemanding.

No understanding ...

[Did67]

except maybe in pellet or wafer heating where we also have a "fuel flow" which can give an idea of ​​the power ...
...

Affirmative.

And the "controlled combustion" log boilers (microprocessor) too.

I have just leafed through the BLT reports for log boilers of this type.

So, yes, you "fill" the boiler and the electronics "control" the combustion, by regulating the primary and secondary air admissions and the smoke extraction.

So in this case, the powers are very clear. The processor is in control and regulates.

Note that in the two PVs that I just went through (an ETA and a Guntamatic), the power measured is very very close to the nominal power announced by the manufacturer (so the piloting is not kidding!). The yields with beech logs (analyzed before the test; C, H, O, N content and humidity; hence the theoretical PCI of the dry fuel and then converted into the real PCI of the fuel) are between 90 and 92%. The filling corresponded to test durations of about ten hours (the heat contained in the boiler water at the end is taken into account in the calculation of the output).

The tests were also done at half power and at the lowest power.

So, in these "piloted" devices, everything is clear: the powers, the yields ... Whether it is pellets, chips or logs ...

For the others, I don't know how the quantity, the quality of the wood we put and the "draft" are determined ????

[Christophe]

Found (thanks Philippe) also on the Deville website: http://www.deville.fr/page2.php

Nominal Power

Deville commits to the announced performances and powers.

The DEVILLE laboratory was the first in France to obtain NF BOIS authorization. Thanks to this authorization issued by AFNOR, DEVILLE can affix the NF BOIS mark on its products and, by this fact, undertakes to respect the performances it announces for its devices. (Performances which are regularly checked by bodies notified by AFNOR).

Deville announces real power: nominal power

The only power announcement in accordance with standard NF D 35 376 (standard concerning all wood / charcoal insert fireplaces) is the nominal power. This nominal power is the TRUE power obtained by the user under normal conditions of use and this nominal power is the ONLY one that meets the needs of users. Certain announcements referring to maximum or instantaneous powers can deceive the purchaser of a hearth or an insert since these powers have only a very ephemeral character.

We notice the power differences between the “nominal” and “maximum” powers, which can, if necessary, cause great dissatisfaction among the user who in fact relied on an “illusory” power.



It is easy to see through this standard operating curve of a fireplace or an insert that the maximum power obtained can reach 250% of the advertised nominal value, i.e. for a device with a nominal power of 10 kW, a maximum power of 25 kW (obtained in a very short time).

This curve also proves that the power restored to the habitat, therefore to the user, is an average calculated according to the standard over a period of approximately 3 hours.

Standard NF D 35-376

DEVILLE fireplaces and inserts are all, without exception, in compliance with standard NF D 35-376.

Acquiring a DEVILLE device is the certainty of obtaining the best guarantees of reliability, security and comfort that only a large manufacturer like DEVILLE is able to offer you.

A rating plate affixed to each device indicates its nominal power and its specifications.

I am very satisfied with these explanations. It remains to be seen what the other manufacturers are announcing ... and how the performance is defined!

[dedeleco]

First of all, the DTU and AFNOR freak me out because if we don't pay full price, we never have their full text, to the point that we wonder, given the price, if the professionals have read them, seen certain installations where they do not respect basic physical common sense !!! (even with a legal expert),
The DTU on performance remains secret to me !!!
We note the absurdity, "put large vents, 300cm2" to the point that in very cold and windy, it is absurd to heat, everything goes outside so as not to risk CO.
Result 300mts per year in France by CO, according to the TV, even in a church !! The poorest people close these absurd air vents with cheap devices, with basic errors, and suffocate !!
And this continues, the Lobbies and insurances say: it is their fault they did not respect the rules, they closed the air vents of the rooms !!!
A heating, good, even totally closed vents, should not risk suffocating its occupants, otherwise it should be out of the norm and prohibited !!
We should measure the CO in the worst possible conditions, with air vents, and wind preventing the chimney draft !!!
This is not the case !!!!
In addition to the DTU of the building being secret, we cannot verify if the professional knows and respects them !!!
Also; the performance is subsidiary in my opinion compared to the life of the users.

For a stove or an exchanger, the efficiency decreases with the heating flow as with the temperature of the burnt gases which leave in the chimney, waste heat.
So if we assume that everything is burnt, the temperature of the gases leaving the exchanger gives the efficiency by relating it to the temperature of the hot gases before the exchanger and to the flow of incoming air .
At low combustion speed the efficiency is always much better if the burnt gases do not come out hot !!
An insert, or stove, often with a bad exchanger has a very poor performance with high combustion with many logs. It becomes good with slow combustion and little wood for sure !!
I don't see a manufacturer giving this crucial information !!!
Installers often apply rules that they misunderstand and therefore do not realize when they make application errors.
We ask ourselves basic questions without ever having clear, coherent answers.
The operations at 9KW and 22,5KW have nothing to do with temperatures, the last one being loud, function of the air flow of the circulator with very poor efficiency to see the exchanger pretty rudimentary !!