clearances: all science or some manufacturers more conservative than others?

[mar13]

I read the article about clearances ( https://www.hearth.com/talk/threads/wood-stove-wall-clearances-primer.147785/ ) which was informative about how clearances are determined. I begin to wonder, however, if certain manufacturers are more conservative than others when listing clearances and don't necessarily follow the method described in the article. Or do the designs make that big of a difference?

In my research for a low-clearance mid-size cast iron skirted steel firebox I 've done a lot of comparisons. For example, the Jotul F45 has corner clearance (double walled pipe) of 11 inches to combustibles. The PE Super Series/T5 have only 4 inches, yet have a higher max BTU ratings than the F45 (epa.gov). The Napoleon 1400 series (steel only and cast iron skirted) are both at 4 inches. The PE Summit Series is only 5 inches. The cast iron clad Blaze Kings (Ashford 20 & 30) also have lower max BTU ratings, yet wider clearances. The firebox volumes don't seem to explain it all.

I could easily believe either story: (1) It's purely design and identical lab methods were used to determine clearances; or, (2) all companies use such testing methods but then some add a fudge factor to play it extra safe.

This is just hypothetical thinking as I'll stick to what the stated clearances when seeing what fits. I would be curious, nonetheless, to know what makes such differences in their designs other than simply steel vs. cast iron.

Thinking too much....

 

[PaulOinMA]

Up to manufacturer with, I expect, LOTS of input from their legal department.

Federal regulations are in the Code of Federal Regulations (CFR) at 16 CFR 1406.4: " ... Appropriate distances are to be determined by the manufacturer …" (footnote to 1406.4). This is the section of the CFR that's the Consumer Product Safety Commission (CPSC).

https://www.gpo.gov/fdsys/pkg/CFR-2018-title16-vol2/pdf/CFR-2018-title16-vol2-part1406.pdf

The company needs to have data available on how recommended clearances were determined, and that has to be provided [16 CFR 1405.5(c)] : " … (c) Rationale. Manufacturers shall provide to the Commission a statement of how the distances to combustibles required to be stated by § 1406.4(a)(1) were determined …".

This is the type of stuff I did for a career. Fun, huh?

 

[PaulOinMA]

If there's a trade association for manufacturers (I have no idea) this this is the type of topic I'd typically see addressed by a working group to come up with some guidelines for industry.

 

[PaulOinMA]

Just thought of something. The footnote to that section of CFR gives the Federal Register (FR) references to where the regulations were finalized and amended. It is:

[48 FR 50706, Nov. 3, 1983, as amended at 62 FR 46667, Sept. 4, 1997]

Wow. Old regulations. Can search to find those Federal Register references, which should contain a preamble that gives the background of how those regulations were promulgated, including industry comments and government reply and decision. I may get more coffee and do that.

 

[jetsam]

Oh lordy, I'd rather assign a random numeric value to every letter of the alphabet and then total up every character in the phone book with a pencil.

Since you are kindly translating this stuff... the only standard is "the manufacturer says X distance is safe, and has a piece of paper explaining why they think so" ?

 

[PaulOinMA]

Here's 11/3/1983 FR: https://cdn.loc.gov/service/ll/fedreg/fr048/fr048214/fr048214.pdf.

This is interesting. You can submit a Freedom of Information (FOI) request to ask for how the clearances were determined for whatever you are interested in. The process is generally one of:

(1) you ask for any and all information relating tp the determination of clearances you're interested in (don't cast too wide a net … will take forever to get a reply);
(2) CPSC gathers what they plan to send out to address your request;
(3) that gets sent to the company to redact anything that company deems confidential (may be a back-and-forth between company and CPSC); and
(4) reply gets sent to you.

 

[PaulOinMA]

Since you are kindly translating this stuff... the only standard is "the manufacturer says X distance is safe, and has a piece of paper explaining why they think so" ?

Pretty much. Though we like to think it's more sophisticated than that.

Here's an example … You know all those nutritional supplement ads on TV with the disclaimer in fine print on the bottom of the screen for a millisecond that the data hasn't been reviewed by FDA? That's because of the Dietary Supplement Health and Education Act in the 1990s, affectionately known as DSHEA.

https://en.wikipedia.org/wiki/Dietary_Supplement_Health_and_Education_Act_of_1994

The manufacturer just has to have data available which THEY BELIEVE supports their claims. Ain't government a wonderful thing?

 

[PaulOinMA]

Looks like the data does have to be submitted, though. I'd like to think that if I submitted PaulOinMA's Magic Stove with data showing that I can overfire the thing to 1,000 degrees 2" from a combustible that it'd raise a red flag at CPSC.

 

[jetsam]

Here at the Jetsam Stove Company, our process is not confidential and we don't mind sharing it with you, because it is also awesome.

First, we are always hiring. You know the candidates who are remarkably terrible? Maybe they lied about every item on their resume, or during the interview they told a long story about how every boss they've ever had was out to get them? Well, we hire that guy as a Quality Observer, which is a work-from-home position.

We then install our development stove in his house, as well as the Quality Assurance Couch, which is flocked in the finest Rayon. We load the stove with a full load of energy logs. Our Quality Assurance Technician calibrates the couch distance to 48" and carefully adds two gallons of Quality Assurance Fluid (kerosene) to the firebox. The Quality Assurance Technician then returns to the office and lights the stove with the Quality Assurance Remote Detonator. The Quality Observer remains on-site to observe.

The next day, if the Quality Assurance Couch is still there, it is moved one inch closer to the stove and the process is repeated. This kind of real-world safety testing is just one reason that everyone is talking about us!

 

[PaulOinMA]

Jeez, I thought you were serious for a second.

I've seen enough screwy stuff in the past that had me shaking my head in wonder.

Here's a story from my late dad:

He was an aeronautical engineer specializing in survivability. Needed ballistics testing on a item from a supplier in the 1970s. Went down to the supplier and they set up the item downrange at firing range. Guy shows up with a rifle, lays down, and takes aim at the piece. My father was dumbfounded and asked what they were doing.

Ballistics testing.

My dad had to explained that it needed to be a controlled environment where they know muzzle velocity, projectile weight, and a ton of other parameters.

 

[jetsam]

I was in the military and saw an unfathomable amount of nonsense related to things being "mil-spec". Like a $90 transistor, available at Radio Shack for a dollar, same part, same manufacturer, maybe even the same lot. However, ours was MILSPEC, tested to meet ridiculous combat-ready parameters devised by someone who has never actually seen combat OR a transistor.

The difference between those identical parts is an insane certification process whose actual purpose is to see if your company's owner has a friend or relative in DC or not.

Things were probably a lot more sane in the 1970s if they were just testing stuff by shooting it!

 

[begreen]

Low clearances are a competitive advantage. It's in the manufacturer's interest to have the lowest, safe clearances possible. This requires extensive certified lab testing which is not cheap. Many manufacturers will do this internally first and then have the certified lab corroborate their results.

 

[bholler]

Ok guys yes manufacturers spec out the clearances they feel are safe. But then the stove is tested to see if those clearances are infact safe. If they pass great ifvthey dont they have to paybto be retested at a different clearance. So yes i am sure they add a bit of a margin to the clearances. But you want a bit of a margin anyway.

 

[bholler]

And like bg said above me they are not pickingbthose numbers out of thin air. They determine them by inhouse testing so they can get as low as possible while still being sure they will pass the tests and be safe.

 

[mar13]

From a footnote: "Appropriate distances are to be determined by the manufacturer. The Commission expects that test procedures utilized by a nationally recognized testing organization would be suitable for determining appropriate distances."

 

[KennyK]

Low clearances are a competitive advantage. It's in the manufacturer's interest to have the lowest, safe clearances possible. This requires extensive certified lab testing which is not cheap. Many manufacturers will do this internally first and then have the certified lab corroborate their results.

I spoke to Tom at Woodstock (the owner or one of the owners I believe), about why the Fireview has such large rear clearance requirements. To summarize, he basically said that they did the testing a long time ago when they didn’t have the capability to do as much metal work as they now do in house, and would certainly be able to build a rear heatshield nowadays that would significantly reduce clearances. However the time, effort and money to get all this tested has been something they just haven’t been able to do with all the other business they have. I suppose that with the popularity of their newer stoves with much closer clearances they fill this need a bit.

 

[webby3650]

I spoke to Tom at Woodstock (the owner or one of the owners I believe), about why the Fireview has such large rear clearance requirements. To summarize, he basically said that they did the testing a long time ago when they didn’t have the capability to do as much metal work as they now do in house, and would certainly be able to build a rear heatshield nowadays that would significantly reduce clearances. However the time, effort and money to get all this tested has been something they just haven’t been able to do with all the other business they have. I suppose that with the popularity of their newer stoves with much closer clearances they fill this need a bit.

My Fireview has a rear heat shield. The clearance is still pretty far with it installed. Can’t get much closer anyway, since it’s a rear exit only.

 

[PaulOinMA]

… I spoke to Tom at Woodstock (the owner or one of the owners I believe), about why the Fireview has such large rear clearance requirements ...

Just thought of something …

The fact that I didn't find set, specific testing clearance requirements all products must meet (they may exist, I just haven't found them), shows that Tom and other owners are doing the right thing. We live in a reactionary regulatory environment here in the U.S. in many ways. That is, something bad happens and government steps in and sets regulation.

What I mean by that is … people getting killed in cars? Seatbelts. Deaths still too high? Airbags.

Self-regulation for these products has been working so far, as highlighted by the fact that the last FR notice reference for promulgation of regulation for these products was over 20 years ago.

What would happen if a product(s) were shown to lead to house fires and deaths when installed as recommended by the manufacturer(s)? Probably an investigation to see if that is a one-off event or there is a fault in the system as it exists. That may lead to regulation specifying the tests all products must meet.

For example, that's what you see on the E.P.A. side of regulating these products. [Dealing with multiple regulatory agencies for a product? Oh joy!] Atmospheric pollution is an issue, so we see E.P.A. stepping in an area they have jurisdiction over and setting standards for products.

Does Tom and other owners want to go before a public, senate committee investigating deaths (worst case scenario)? I'd rather stick a fork in my eye.

In short, our system is many ways hand's off (though a lot think otherwise) unless there is a reason for government to step in.

 

[begreen]

It's not self regulation. The stove is tested to a standard in order to get UL certified.
https://standardscatalog.ul.com/standards/en/standard_737

 

[PaulOinMA]

Thanks. So, there is a specific test with stated temperature at certain distances from a device to determine allowed clearances? Then there is a set standard for all products? I'd like to read the U.L. test requirements.

 

[PaulOinMA]

Who came up with the U.L. tests?

If industry worked with UL to develop the appropriate testing for the products, that's what I mean by self-regulation. It's not government-mandated regulation specified in the CFR like for a lot of products.

 

[Rearscreen]

We live in a reactionary regulatory environment here in the U.S. in many ways. That is, something bad happens and government steps in and sets regulation

The Government doesn't step in as far as electrical code. It's actually a flexible system and I believe a good one. Aircraft, trains etc. yes they do step in. Many lives at stake. But a house fire caused by electrical problem? The NEC updates based on causes and learns from them. What is interesting, the code can change year to year. One year they can say (for instance) all electrical wired to a bathroom must be GFI protected including lighting. Problem is, if it trips using your hair dryer, you are in the dark. So, they changed it.

 

[begreen]

Yes, you are correct, you mentioned Tom specifically at first and I was thinking you meant his company acted individually. The testing standards for many products, tools and materials are a collaborative effort between industry, stakeholders and science. In the US two big testing labs are UL and OMNI.
https://www.ul.com/aboutul/

 

[PaulOinMA]

Yeah, that's how I'm using self-regulation. If it doesn't work, then Big Brother steps in.

 

[KennyK]

My Fireview has a rear heat shield. The clearance is still pretty far with it installed. Can’t get much closer anyway, since it’s a rear exit only.

A Fireview without a heatshield has a rear clearance of 30 inches, with the heat shield the rear clearance is 18 inches - still a pretty large clearance. I believe the Fireview 205 UL testing was done in 1995 or so (I think the 205 came on the market in 1996). The optional FV heat shield is pretty small, and I believe what Tom was saying was that with their much greater ability to work with steel now, they could design a heat shield now that would allow the Fireview 205 with heat shield to pass UL testing with a much closer rear clearance, however the whole stove with new heat shield design would have to go through an entirely new UL testing process.