When did this come about? Draft hood question

GW

I’ve never seen this, maybe I’ve been napping.

DZoro

Oh yeah, you have been napping. That is the invisible offset. With that offset you now don't have to look for CO gases or others it is right there in front of you! Simple and convenient for the death investigators to help find the cause

ch4man

you must be well rested....those have been around for a long time.. you had one heck of a nap Mr Vanwinkle

GW

hahaha I don't do many water heaters anymore, they have drifted into the commodity category. OK thanks for the update, back to rest now.

captainco

If you are referring to the downdraft disc inside the drafthood, it has been there quite a while.

icy78

> @captainco said:
> If you are referring to the downdraft disc inside the drafthood, it has been there quite a while.

Downdraft disc is a backdraft damper of some type? Powered? (Like is supposed to save you off cycle tank losses?)

Bob Harper

The round disc inside the draft hood serves two purposes: it deflects downdrafts out the hood (not very aerodynamic, is it?) and it retards the escape of flue gases and thus buys a fraction of one efficiency point. They went from bad to worse.

GW

Ok thanks. This is an install that is causing me lots of time and energy. We didn’t install the water heater but we did install a new Buderus GC144-3. The lady is getting some bad fumes, likely inadequate draft. She tells me she has 5’ snow drifts, which is the primary reason why we didn’t install a High Efficiency boiler. Boiler draft drifts between 0 and neg 03.

The chimney is an odd 23’ tall exterior “side of the house” set up. It’s a small cape. Top of chimney seems close to peak of roof (elevation that is). Horizontal distance is maybe 15 feet

We are discussing installing a fields booster. It’s so bad she is not running the boiler. The chimney contractor installed a 5” ss liner prior to my involvement. They are not interested in the lack of draft.

The other day the lady emails and says she’s getting the noxious odors again, with the boiler off.......so I’m still scratching my head

She seems to think the boiler’s gas valve is leaking gas. It’s been a real struggle. I shut off the gas shutoff.

That’s when I noticed the friendly little baffle.

So maybe we have a backdraft issues going on.

It’s been a real pain

Bob Harper

If you have a suitable boiler, why not just install an indirect tank and let the boiler vent alone? Sniffers should be able to distinguish btw fugitive gas and aldehydes (and ostensibly CO). If this was a gas conversion to oil, you can still get oil exhaust odors down the chimney around the liner into the building. If that's what it is, they might be able to stop it by insulating the liner with a cementitious UL listed liner insulation such as Thermix. At 74 MBH input derated 20% for a corrugated liner a 5" liner at 20+ feet should be ok even using a single walled connector with a long lateral offset, according to the GAMA sizing tables in the code. However, codes do NOT guarantee performance, which is why we must test.

GW

Thanks. It’s been gas from the beginning. We removed the 50 or so year old gas boiler. At one point I myself sensed the gassy odors, and I picked up a few ppm Co in the basement too.

I’m just afraid that if we do the inducer the problem won’t go away.

Pic of the system attached

Jamie Hall

The vague concern I have, Gary ( @GW ), is that that chimney just isn't pulling enough consistently. And no, I don't know why. The idea of an induced draught fan isn't a bad one, but you'd want to have it after the junction between breeching for the boiler and the breeching for the water heater, so it pulls on both -- otherwise I see a potential for it blowing down the water heater breeching rather than going where you want it to.

Have it wired so that it runs whenever either the water heater or the boiler runs -- you'll need a relay or two there.

And you -- or somebody -- did such a nice job on that breeching that it seems a shame to have to fiddle with it.

Just an idea...

GW

Yes Jamie thanks, we need to redo the vent run. It’s been a real pain.

Bob Harper

You can't create positive vent pressure on CAT I venting. You can put an exhaust fan at the flue gas outlet on top of the chimney interlocked to the gas controls. Even an "inducer" creates positive vent pressure on lateral connector runs and the first few feet of chimney so you have the potential of blowing flue gases out the joints. If the liner is sized properly and there is no competing air/ depressurization issue it should vent by gravity alone. What you can do is to block off those draft hoods and install double acting barometric dampers with spill switches and set the draft then perform combustion analysis. "Picked up a few ppm.." could be from curtain effect on that WH draft hood, which the baro. would correct.

Bob Harper

From the Father of heat and building science back in 1795 from Woburn, Mass. :
“Those who will take the trouble to consider the nature and properties of elastic fluids, of air, smoke, and vapour, and to examine the laws of their motions, and the necessary consequences of their being rarified by heat, will perceive that it would be as much a miracle if smoke should not rise in a chimney, all hindrances to its ascent being removed, as that water should refuse to run in a syphon, or to descend in a river. The whole mystery, therefore, of curing smoking chimneys, is comprised in this simple direction; find out and remove those local hindrances which forcibly prevent the smoke from following its natural tendency to go up the chimney; or rather, to speak more accurately, which prevent its being forced up the chimney by the pressure of heavier air of the room.”
The Collected Works of Count Rumford, Volume II. Practical Applications of Heat. Page 224. By Benjamin Thompson. 1795

ch4man

Bob, thats awesome.....

GW

Very good I love the smart old dead men. I did block off the boiler’s hood (no effect on draft) yet I didn’t also try blocking the water heater

I’m familiar with the fields MG1 and the spill switch’s

What’s super odd is she’s getting an odor when the boiler was shut off.

I have never heard of a fan on top of the chimney. Where can I get more info on that?

Bob Harper

https://enervex.com/

https://www.exhausto.com/products/Fans

http://www.fieldcontrols.com/chimney-top-draft-inducers?page_id=434