Oh, I was thinking again about draft hoods.....Boilerpro

Boilerpro_3

I suspect that draft hood design has a big impact on standby losses into the room on a stack damper equipped boiler. I have noticed 3 common designs, the classic mushroom, the low built in type with the relief opening just below the top of the heat exchanger, and the very low built in type with the relief opening which is below the heat exchanger (like on some Lochinvars, for instance). With the tall mushroom, a strong draft continues to be present during the off cycle to pull heat off the heat exchanger and then dump it into the room. This draft height is probably about the same as the connection to the chimney. With the lower built in types that drop partially below the heat exchanger, the draft is reduced through the boiler during the off cycle since the relief opening is lower than the breeching connector, this should reduce standby losses to the room. With the design where the relief opening is below the bottom of the heat exchanger, where the inverted "U" formed creates a heat trap when the damper is closed, there is little or no draft during the off cycles. I suspect that standby losses on this type of drafthood would be at a very minimum.

Just thinking a bit here.

Boilerpro

bill clinton_3

drafthoods

Have had similar thoughts and believe you are correct. My understanding is that efficiency advantages wouldn't show up in AFUE ratings because, when vent damper is closed, you get draft hood spillage into the room and this is counted as useful heat.

However, if so, why haven't manufacturer's of superior designs been touting the advantages?

Bill

Boilerpro_3

I was thinking the same thing

won't show up on AFUE and won't show up on commerical boiler ratings, since cycle efficiency isn't measured.

BP

Kal Row

because

manufactures have had enough of lousy venting and co poisoning , and are dragging us kicking and screaming into the world of sealed combustion - where all this is moot

jim sokolovic

This is going to drive some people crazy...

but here is how the AFUE tests are run:

With the "mushroom" hood, temperatures are taken in the flue pipe at set time periods during the off-cycle portion of the test, which are factored into the calculation. Generally, the faster the "cool down", the better for the final AFUE result. There is no alteration of the relief opening during this test.

With the integral hood (at whatever height relation to the heat exchanger) the relief opening is blocked off completely (at the end of the on cycle part of the test) and a slight blockage is imposed at the end of the stack pipe (to reproduce in the stack the same CO2 that the boiler normally produces in the flue). Temperature readings are taken during the same time periods of the off cycle portion of the test, in the portion of the stack pipe that has now essentially become the flue pipe. Once again, a faster "cooldown" is better for the AFUE result.

No actual vent damper is installed during any of these efficiency tests. The dimensions, open areas, and other specifications of the particular vent damper that would be used in the field are entered into the computer calculation.

I would tend to believe that the "mushroom" hood is favored by these methods, but the observations that are presented in this post on the integral hood make sense to me.

Enjoy!

Unknown

What is interesting

is that typically the draft hood located above the equipment versus built in has a lot to do with the Kinkead method of creating some rise before introducing dilution air in order to have some self venting action.

My experience with built in draft hoods is that it is much more difficult to get draft within specified time in order to prevent excessive spillage into the room. It varies with manufacturers. I suspect this has to do with how tight the sections are on their equipment.

Years ago we had three types of design which compensated for increased wiping action into the boiler. The were full revertible flue passages, semi-revertible and top drafting.
Many of the full revertible had difficulty when converted over to gas or oil with venting. Especially the full revertible converted to gas.

As we have tightened up boilers and changed combustion gas travel through the packages, draft hoods have become a problem in many repects. We would in many cases be better off with barometric draft control. We would then see some increased efficiency just because we can control O2, flue gas temps and overall draft.

jim sokolovic

Round and round...

we go, Timmie. Until every single installer of gas equipment is mandated to be proficient in testing the combustion and performing the necessary adjustments, that will probably not happen, in my (limited) view.
In the meantime, we strive to safety test these integral hood designs beyond what the required Standards impose.

Kal Row

sealed combustion should be the law

on the other hand i recently put in one of your sx-150's, when what i really wanted, was to put in one of your vsph's, but could not provide the needed pitch and clearance along a 14ft horizontal run

what we need, is an oversized blower and fresh air bypass option, so that fresh air can be bypassed around the boiler and tee'd back into the exhaust flow with a ventrie tube as not to obstruct the boiler flow,

this way i wouldn’t have to worry about temperature clearance - since the bypass air will cool it, and as long a i have a condensate drain and trap at every low point - i can pitch it up and down six ways to monday

jim sokolovic

And they say kids...

say the darndest things!

Mark Hunt

It may be closer than you think


and why has it taken so long?

Wouldn't it be something if manufacturers along with concerned contractors started pushing for this?

What is the difference between an untrained homeowner and an untrained PHVAC tech?

Answer..........no difference.

Solder joints don't leak, gas pipe or oil line is tight, flue pipe plugged in. See ya'!

It's that easy right? So why would anyone hire a pro if they can do the same installation? No testing, no knowledge of combustion or PROPER venting. What the he** do they need a pro for?

Quoted from Slant/Fin Galaxy manual:

"WARNING: This boiler, gas piping and accessories must be installed, connected, serviced and repaired by a trained, experienced service technician, familiar with all precautions required for gas fired equipment and liscenced or otherwise qualified, in compliance with the authority having jurisdiction."

All manufacturers have similar warnings.

Who is that warning for? The homeowner, the contractor, or both?

What "training" should the "experienced" installer/service tech have? I have attended "training" from nearly every boiler manufacturer there is for their products. Does that mean I am "trained"? Never once was PROPER combustion or PROPER venting discussed. Not ever.

Draft tests consist of putting a match near a drafthood. If the smoke goes up, it's venting. Really?

Timmie posted a situation here a while ago where that match would have been sucked up the chimney, but the APPLIANCE was not drafting. Air from the room was, but the boiler was not.

I agree that our industry is under-trained, but our industry keeps it that way. It's time for that to change.

I don't care how many "CO Experts" alarms a person has in their home. Their CONTRACTOR should be the CO Expert! And the combustion expert. Customers already ASSUME we are! Shouldn't our job be to make sure the "CO alarm" remains silent?

I had to get certified to play with R-22. Seen any deaths from R-22 leaks lately? Not combustion appliances though! ANYONE can play!

Manufacturers put roll-out switches and spill switches on their equipment. WHY? Who told you to and what was the reason? Why weren't they always there?

BTW, can anyone tell me how to test a roll-out switch without destroying it?

Yah, our industry needs to get with it. You are the first manufacturer rep that I have ever heard that come from.

"Until every single installer of gas equipment is mandated to be proficient in testing the combustion and performing the necessary adjustments, that will probably not happen, in my (limited) view. In the meantime, we strive to safety test these integral hood designs beyond what the required Standards impose."

Very well put sir, but you and I both know that "required standards" do not apply to all situations. Manufacturers should not be held accountable for contractor ignorance, let me state that right up front. Manufacturer's legal departments make sure that they have addressed potential liabilities before any document goes to the printer.

"Trained"- Trained for what and by whom?

"Experienced"- For how long and in what?

"Familiar with all precautions"- Where would find these precautions?

"Liscenced or otherwise qualified"- Liscenced by whom, and what does "otherwise qualified" mean?

I am not trying to single out Slant/Fin here, they are a good company. My point is that almost no-one meets those requirements yet thousands of boilers and water heaters and furnaces are installed each day. Thousands more are serviced by unqualified service techs. The industry remains silent.

Better days are coming though.

You can count on it.

Mark H







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Murph'_5

the reasons

The main reasons why I will not choose equipment made by folks who know the difference but choose to stick thier heads in the sand in the name of profit$


RC.

Mad Dog

Gosh!!!! That was a mighty long rant............

whadya just get back from Giffy's, with a few in ya??? Md

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Kal Row

it's going to go down like this

cause once the gov gets involved, then the epa, gets involved

you know, the oxygen sensors you have in you car - in fact many cars now have multiple upstream and downstream of air injection system and on both sides of the engine, plus you have a barometric, and intake pressure, and temperature, and mass-air-flow – all this feeds the computer for perfect combustion

well – stay tuned - “it’s coming soon…to a boiler near you…” – and manufactures are not putting it in for free – lucky – we can second market it from the auto world, that should save a bundle, but it will still cost ya

ps 1-2% oxygen in the flue, guarantees – no CO – yeah – it will run slightly cooler – tough!!

jim sokolovic

Mark and Kal...

Mark - I appreciate your stand on these issues, but once again, I'm just one of the lab techs here. There are questions you have that I am not qualified to answer, in terms of company policy. Interaction in this forum allows me to understand some of the problems that happen in the field on various equipment in certain real-world situations. I can encorporate this knowledge to the standardized tests that are performed as equipment is developed, in hopes of producing better products. Occasionally, when a subject is discussed here that I feel I can contribute to, I do so. Even this limited interaction does not go without grief, from those who do not understand an honest effort to widen one's view of things.

Kal - please offer a more thorough explanation of your "no CO" guarantee, I'm not following the message? Thanks.

Jim Davis

Drafthoods-Compromise plus Compromise

If one would investigate the true developement of drafthoods they would find their original design dealt with keeping pilots from blowing out versus any good venting actions. All drafthoods were round and top mounted and were designed to be moveable. Once installed at minimum recommended heights, some type of none functional draft test was supposed to be taken. If it was felt that this test did not verify adequate draft, the drafthood was supposed to be raised additional height and retested. The built in drafthood design came about in order to install equipment in mechanical rooms with low ceilings. Nothing in the design of a drafthood ever concerned itself with venting issues that occurred in the real world or true efficiency. Drafthoods were technically never approved for use in mechanical rooms with negative pressures. Any device that allows a chimney to be totally clogged and the appliance still operate cannot not be considered a great invention!!

Boilerpro_3

A little more thinking on the safety issue of drafthoods

I would suspect that the very low draft hood design would be considered the safest. Since its opening is about at flame level, a clogged chmey would cause flame rollout. A roll out switch would then provide considerable protection from the equipment operating with a clogged chimney.

BP

jim sokolovic

Blocked Chimney safety...

Our testing shows that the spill switch (usually located on or below the hood) is the safety device that would shutoff the boiler in an event of a clogged chimney or severe downdraft. The rollout switch (usually located above the burner compartment) is the safety device that would shutoff the boiler in an event of a clogged heat exchanger or flue portion, or severe over-firing. Hope this helps.

Boilerpro_3

Jim...

I was referring to drafthood designs like that on the Lochnivar RBN boilers. The relief opening is about at burner level, not near the top of the heat exchanger. There are no spill switches on these boilers only roll out switches.

BP

jim sokolovic

I haven't seen that boiler...

but I can picture the design, as you describe it. Is a single thermally activated safety device located at only one of the two points of possible relief a reliable safety assurance enough for you?

Boilerpro_3

Good question....

However, its approved. I understand even regular spill switches don't work under certain spillage conditions, so the idea of power venting is looking better. It is hard to get away from the simple reliablility of atmospheric draft hood equipped appliances.

BP

Jim Davis

Low hood

Actually these test to be consistently more dangerous in the field because they tend to bring more room air than flue gases.

Kal Row

simple

CO happens when there is not enough O2 to go around,
the causes of this "rich" mixture are many - some really vexing,
at the fine level,

typically O2 left over correlates to CO2, the lower the O2, the higher the CO2, until you get down to zero left over O2, where you are forming CO, because the is not enough air to go around, so just a little over 1% left over, at the sensor, should guarantee, that there was enough O2 to go around all over the combustion chamber,

but, THE BIG BUT, things are not that simple – a problem I call micro-mixture, you’d think that if you have too much air, there would be 100 guarantee of no CO, not true, because when you get into the lean miss conditions (ie the HydroCarbon and O2’s and Heat, are so spread out that they don’t connect – indicated again by rapid rising HC or O2 – (co rise will be much slower)) – you will also get CO, since 1 HC’s (it’s really H2C+junk) might just happen to connect with just one O2, and not the 2 O2’s required to get 2-H2O’s and CO2 – so you get instead h20 and CO, OR, if you are lucky, 2 h2c’s connect with 1 o2, to give you 2-h2o’s and 2 carbons – lucky because, the soot, at least, you can see – so it wont kill ya!! I really should have said Up to 2%, because, probably after 1.5% left over O2, it’s already to lean – and I suspect that number varies with fuel/air temp/press flow speed and Heat-eX temp

Then there is the localized speed and mixture temps that affect the whole heat+fuel+air connecting thing – a clump of cold fuel molecules could suddenly pop apart and demand air that’s just not there, OR, separated fuel molecules hit a cold heat exchanger and clump together (or should I say condense , then on the outside of the clump burns rich, because there’s not enough O2, while the inside of the clump, stays unburned completely, – then, there is the actual air flow, the secret has always been to slow it down as much as possible – so with some excess air, most of the fuel/air/heat connects, that’s why those gas/ceramic/radiant heaters do so well – or the ‘sticker shock city’ vitodens from viessmann

Here, is were, the science get weak – the data is more experience based, than science based, I know, you hate tech analogies, to the auto or jet world – but those engineers have more data on the vagaries of flame fronts than anyone else – auto is akin – because gas/propane combustion dynamics are explosives like gasoline – you can run a car on them, so a lot of the flame front dynamics apply even though the pressures are not the same, and cold engines are like cold boilers – everything condenses
Turbine engines are also akin – because they are external combustion like boilers – with steady continuous flame, (actually oil-burners can gain more from jet engine combustor technology)
so while we are way different from both dynamically, their focus is rapid expansion, whereas, our focus, is heat extraction, there has just got to be a lot of science we can get from both, but, the flame front data has to be carefully extrapolated, to separate the affects, that either engine type’s pressure/flow dynamics, have on the flame data

Hey, even us humans are carbon based life too, we eat HC’s, take in O2 and breath out Co2 and when we get renal failure, the blood can’t carry enough o2’s and things start to get black, real fast – dust to dust… but our combustion is enzyme driven and the temps are to low to be useful – could be good for slab radiant though – hook a bunch of guys up to pex and put a put a picture Catharine Zeta Jones in front of them… ;-) she is sooooooh hot – it will work even if they are gay

jim sokolovic

Wow - queer radiant for the straight guy!

O.K., you added the term "extra" to your low number Oxygen percentage and the CO statement makes more sense. Guaranteed, though - maybe, maybe not. Some burners may need even more excess air. We discussed this a few months ago. I like to see what the richest and most lean CO2 I can run without an elevated CO occurrance (or other negative byproduct, like lifting, flashback, no ignition, etc.) and split the difference for setting the best CO2 for all combinations of efficiency, reliability, and safety.

Kal Row

see i am always learning -

forgot all about lifting, flashback, no ignition, etc, though, this is where we will need new burner technology to make a REAL difference, we have exhausted the burner rail technology – what are you getting – say 9% co2, would be nice to get 12% steady, shaped heat exchangers, down burning with active combustion control is next,
the R and D is so expensive - I can almost (mean almost) justify the cost of the viessmann, don’t know how SF is going to do it, it may be more economically expedient to capitalize on what you already have, and take the mix-down cast iron concept like the Burnham’s revolution or the WM’s CV-gold one step further and offer sealed combustion boiler’s with primary/secondary/injection/teckmar 361 built in, and modular add-a-zone with variable pump per zone manifolds built right on all wired and ready to roll, plus, sell your baseboards with trv’s and bypass tube built-in -- all this combine to save more on a heating bill than just a high-tech condensing boiler will

and even a cast boiler with a corrosion proof coating to handle condensing would do more than fine in the above scenario, not to mention if you modulate, and perhaps even stage sections internally

Kal Row

also check out system 2000 at energykinetics.com

Kal Row

all the new boilers come with a flame rollout protector

so i wonder why we cant just put another vent damper below the hood - this way the chimney and the boiler are closed

jim sokolovic

By \"another\" vent damper...

do you mean a second one, in addition to the one that is on the stack pipe already?

Kal Row

yep

the motors would be wired in paralel and the switches in series - question is, will heat from an air trapped boiler kill the one shot rollout most vendors are using

- might have to switch to the auto reset clicker being used on the hood - with a clicker it would not matter, since it after the dampers open and the pumps run - the boiler will cool down, and the clicker will reset

jim sokolovic

I got your thought now...

I had to go back to remember what the original subject of this post was - with all that talk on CO, training, and Katherine Zeta... :^)

Well, if the vent damper in the flue pipe (on the mushroom style hood) were to fail to open, the spill switch on the hood would not be able to protect against disaster, so you would be counting on the rollout switch over the burner area. If you make the rollout switch auto-reset, the burners could cycle on-off very rapidly - combined with a full blockage of the flue, this would produce one of the worst CO conditions that could exist.

With the occurrence of a vent damper failure in a standard installation, I believe that the burners can still cycle off of the spill switch, but at least there is a point of relief (the hood opening), to allow less hazardous combustion to take place.

Hope I got that right to answer your question.

Unknown

We have enough problems with one

vent damper now you want two. The service people are already leaving the dampers disconnected and jumping out the control to get the system to run. If you put a second damper there will be a real nightmare out in the field.

hr

Say NO to additional dampers!

I agree with Timme, 50% maybe nore are locked open??

Another reason you see them locked oper, even though they still operate, the heat left in a cast iron boiler when the damper slams shut can, and does, cause the spill switch on the divertor hood to pop.

So now the call back options are to move or disable the spill switch, or lock open the damper. One is a liability issue, the other an efficiency issue.

Also vent dampers seem to fail a lot more often than spill switches. Even the IMPROVED versions.

Throw in a low mass or low water content boiler, multi zoned, micro loaded, that cycles hundred's of times a day, and plan on a yearly, or less, vent damper failure call. Or.... lock em open.

So now it becomes a money decision also. My call back labor, or the owners fuel cost difference.

Unless the damper manufactures want to pay reasonable labor allowances?? I thought not! I suspect manufactures and contractors are of different opinion on this

hot rod

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Mark Hunt

Is it possible


for flue spillage to occur on one side of a draft hood and not the other, making a spill switch obsolete?

Mark H

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Unknown

Mark, tht is why often

if I retrofit a spill switch on a unit I will use two of them in series. One on each side.

bob_25

spill switches

yes. some power venting kits like tjerlund come with two manual reset spill switches. you wire them in series. that is what is required for just a little 3" diverter.

Kal Row

ok, ok, so...

we are back to horizontal diverter with a long drop tube as the only simply way to contain the boiler heat?

Unknown

Kal, What is a

"long drop tube"????

jim sokolovic

He's talking about...

the integral draft hood that extends down below the bottom of the heat exchanger, that theoretically contains the heat within the boiler during off cycles.

Kal Row

well

that's what i thought Boilerpro's first ideas was,
to use a horizontal diverter, with the vent damper past it of course, but then to extend the downward facing open end, down to almost the floor, so when the damper is open exess draft can come up through it but then the damper is closed the hot air from the boiler will be trapped at the top of it

jim sokolovic

On your diagram, Kal...

I notice you included a baffle, extending downward, right over the "drop tube" - have you actually seen that on a hood? That's a bad place to put one, I imagine. But some would say, there is no good design for these anyway!

Kal Row

seen some with, and some without

they are about 1/3rd the diameter

Kal Row

i was raking my memory trying to remmeber

when i saw one like that last and i realized the it had
been made out of two elbows cut out 1/3rd on the side and screwd together (UGH!) so that might explain what i thought was a baffle - (dont worry - i did replace it - but it stuck in my memory - just some of the crazy things you see out there)