Draft hoods, Stack dampers and Standby losses

Unknown

on Draft Hoods

Boilerpro

Draft hoods, Stack dampers and Standby losses

Looking at a steam boiler install where standby losses are a major issue and it got me thinking again (Oh, no!). I understand that stack dampers help eliminate losses through the stack through the draft hood relief opening from the boiler room. However, even with the stack closed on most draft hood designs, heat from the boiler still spills into the boiler room. This still seems to be quite a waste, especially when there are other boilers or fired equipment in use in the room and they take this heated air and use it for combustion or for the operation of thier draft hoods. The Lochinvar RBN series boilers have a draft hood relief opening that is below the heat exchanger, which should create a heat trap, reducing the standby losses. For "mushroom" and built in draft divertors, has anyone ever seen a design where an additional stack damper was used to close off the drafthood, or some other method of helping eliminate this standby loss?

Boilerpro

Bill Clinton

stack dampers

Ah, boilerpro! You raise an issue that has bugged me for ages. Viesman makes, or at least at one time made, a boiler with optional damper that closed before the dilution opening, sealing heat in. I've also seen commercial water heaters with motorized dampers before the dilution point.

On the other hand, I suspect the low relief opening you mention on the Lochinvar helps a good deal. Other boilers have adopted them too. I've asked why the trend that way, and get few answers, but I think this is the reason.

Bill

Boilerpro

Say Bill..

What are some of those other makes with the low relief opening? The Lochinvar is the only one I've seen so far. The built in divertors on the residntial Dunkirk's, Weil's etc. Don't drop down to the combustion chambers.

Boilerpro

Steamhead

Interesting question

yes, the air drafting thru the boiler and out the draft hood when the damper is closed is a loss, but nothing compared to a three-story coal-designed chimney sucking air thru the boiler during the off cycle. And that off-cycle air drafting thru a non-dampered boiler has to come from somewhere- most often the living space we're trying to heat.

I'd still go with the damper.

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Boilerpro

I would too, but maybe two! NM

Steamhead

I remember

some old, old gas conversion burners had air-inlet dampers. This would seem to be the best place to put a damper to prevent the sort of drafting you describe. But I've yet to see an atmospheric boiler that could be set up that way.

I doubt you'd have that problem with a sealed-combustion unit. Maybe that's the way to go in your situation.

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Boilerpro

Yep, I take care of a big old steam boiler with one of those.

I just like to keep my equipment simpler than sealed combustin units....all the additional components to go wrong. Induced draft and sealed combustion has been a boom for forced air.... all sorts of service work that wasn't necessary on older units. I bet a big chunk of all the energy they save goes to making and shipping replacement parts and the fuel for the service trucks.

Boilerpro

[Deleted User]

The saved energy

probably goes to make replacement dampers for those that fail.

One of our Techs was at a gas water heater distributor's shop the other day. He was shown a new shipment of dampers that included the jumper to use when the damper failed. That is what I call "value engineering."

Boilerpro

Haven't seen that problem with the Effikals..

mainly with the Honeywells.

Boilerpro

John Ruhnke1

Get rid of the draft hood

Boiler Pro,

Try getting rid of the draft hood and install a barametric draft control in its place. Not only is that excess heat costly in fuel bills but it is very dangerous in CO. IT CAN KILL SOMEONE GIVEN THE RIGHT CONDITIONS. Buy a co meter and draft gauge. Take a class to know how to use them. Why take a chance with other peoples lives. Draft hoods are often dangerous because it is very difficult to control draft with them. The only problem you might have is with a standing pilot. The reason draft hoods are installed is to stop the pilot from going out. Thats the only advantage they have. Very seldom is the pilot going out an issue. If that happens, install a star cap on the chimney.

JR

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

hot_rod

I'll take a

sealed combustion over a vent damper any day. In addition to the decreases flue loss you get rid or the combustion air requirements that constantly suck heat from the boiler. Regardless of whether the damper is open or closed.

I've seen large commercial boiler rooms in Utah with piles of snow inside the boiler room next to the louvered combustion air grills. Talk about heating the "great outdoors" May as well have the boiler sitting outside!

hot rod

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

John Ruhnke1

DANGER! Excess heat is the flue gas flowing in wrong direction

Very Very Dangerous.

When heat poors out of the draft hood that means you are getting flue gas leakage. FLUE GAS CARRIES CARBON MONOXIDE. The flue gas should NEVER EVER poor out of the draft hood. The flue gas should go up the chimney 100% of the time. You have a serious venting problem. Even if 99% of the time the flue gas doesn't build up to a dangerous level, it only takes one time to kill someone. One time only. NO SECOND CHANCE, THEY ARE DEAD. Sorry to shout, I just don't want to see any more deaths.

JR

JR

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Boilerpro

John...

Heat poors out of draft hoods when the burner is off and the damper is closed because the boiler is still drafting through the hot heat exchanger when the draft hood opening is above the combustion air inlet to the burners. I have not been speaking about heat pooring out of drafthoods when the burners is on....YES THAT CAN BE VERY DANGEROUS... if it continues for more than a minute or so for the chimney to warm up and begin drafting.

Boilerpro

Steve Levine

The boilers are approved

with the draft hoods they are supplied with. They should not be altered in any way. Boilerpro is correct, the spillage shold only occur after the burner shuts off, and then the vent damper closes. If there is spillage while the burner is on, there is a vent damper or chimney problem. Unfortunately, the spillage is not listed as losss of efficiency, as it is 'assumed' the the spillage contributes to the heating of the space. I guess most wpould agree that this is essentially true in many residential applications, but I'm sure not in all.

Steve

Steamhead

Found a ruined Honeywell damper today

on a small Slant/Fin Galaxy steamer in a rowhouse. The motor had burned out. The damper blade was stuck- fortunately in the full-open position. But the damper itself was NOT the cause of the problem.

SOMEONE HAD SCREWED THE GAS REGULATOR ALL THE WAY DOWN!

I stopped the Testo when the stack temp quickly rose past 650 degrees. Obviously this was the cause of the burnout. And you could see where the gas had burned inside some of the burner tubes. This was due to all that excess gas on startup. Sometimes the flame would roll out momentarily and enter the air shutters- but not enough to trip the rollout switch.

Fortunately we got to this one in time. The owner realizes how lucky he is.

Moral: If you find a bad damper, check everything on the boiler to be sure something else isn't wrong. I'm sure that's already standard procedure for Wallies!

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

John Ruhnke1

You can't get proper draft with a draft hood.

Steve,

You can't get proper draft or venting with a draft hood. The flue gas can easlily run backwards through the draft hood and out the bottum of the heater. I have seen this with my own eyes. Even with a power venter, it still won't work. The heavier air, room air gets drawn up the chimney and blocks the lighter flue gas air. The flue gas air then actually flows backwards. When this happens, no venting correction will solve the problem. THE ONLY SOLUTION IS TO GET RID OF THE DRAFT HOOD AND INSTALL A BAROMETRIC DAMPER. I know the problem doesn't always happen. It does happen alot though. CO KILLS, I REPEAT CO KILLS. I don't care about your stupid codes and regulations. I just want to keep my clients living. Remember TEST TEST TEST and TEST. If you properly test for draft you will see what I mean.

JR

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

Boilerpro

Steve.....

I've been thinking of enclosed boiler room applications with dedicated outdoor air with modular boilers. Virtually all this spillage, along with the heat lost from the poorly insulated jackets found on most boilers, would all be waste. A different drafthood design, dual dampers, etc. and better boiler insulation would certainly help reduce this waste. Wponder what a "typical" number for this loss is? I bet it could be done with little increase in cost and complexity of equipment. In the rural areas that I serve, induced draft boilers, electronic ignitions and boiler controls tend to be a major source of headaches, especially when mixed with propane and unstable power supplies.


Boilerpro

Boilerpro

Thanks for the tip... NM .... Boilerpro

Steamhead

Didn't come thru

try again, Tim.

To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"