Spill switch tripping is a flue inducer necessary here?

Doone

My collector hood spill switch keeps tripping, on new W-M EG 55. I installed a cap on the chimney after the first incident a week ago and system worked fine for the next week even through the 0 degree temps and high winds. Then this morning it tripped again. I feel cold air coming out of the vent when the damper is open. There are no fans or other negative pressure items running. Chimney, clay lined, is not obstructed and I never had this problem with the old system. Is a flue inducer called for?

Jamie Hall

"Cold air coming out of the vent...". Somewhere, somehow, something is pulling air down the chimney and it's going out somewhere else. You really need to find out what and where, and solve that problem before you begin to think about inducers or anything like that.

You also absolutely must have a CO detector there. If the spill switch is tripping, it's because combustion gas is coming out of the draught hood into the house -- and that's lethal.

KC_Jones

Doone said:

Chimney, clay lined, is not obstructed and I never had this problem with the old system. Is a flue inducer called for?

Did the old boiler have a spill switch? If not you could have had this problem for years and not known. Is this chimney an interior or exterior chimney?

Doone

Outside brick chimney, clay liner. 12 feet of inside 7 inch pitched flue pipe. There wasn't a spill switch on the old boiler and yes I have a co detector. Chimney man says chimney needs cleanout, he will also install an access door at bottom of chimney (there is none there now) for future cleaning and inspections and replace standard cap with a turbine cap, but I am wondering if I should also install flue inducer as added measure to move combustion exhaust at cold startup. Thanks for all thoughts and advice.

nicholas bonham-carter

Is the crossesectional area of the chimney large enough for the boiler flue pipe?--NBC

Doone

Its the old 7 inch steel flue pipe going in to a 9 inch chimney flue

Jason_13

Check combustion air. Is there a window you can open temporarily to see if problem goes away. I was on a job a few months ago that had about 7 ft of vent pipe in basement to chimney. Man had a big bucket under draft hood to catch all the water and had ignition issues. His bigger problem boiler was short cycling so bat the top of the chimney never got warm enough. A company suggested an inducer. He finally changed boiler to properly sized and problem went away. Boiler is not running 2-4 minutes anymore. Now running 10-12 minutes but problem is gone.

Bob Harper

I've never seen any 9" ID terra cotta square flues--is this round TC? A std. "8x8" flue as used in 99% of homes with masonry chimneys typically measure about 6.5" square which is less than a 7" round in capacity. 12 feet of cold exterior chimney isn't helping. Cold backdraft at standby means you need to fix the house and the chimney should work. Draft pressure? Combustion analysis? I see it is rated for 200 MBH input--why so big? It also calls for a 7" x 20 ft min. chimney. The manual calls for performing a worst case depressurization test before installing. You cannot use anything that will pressurize the flue. You can use an exhaust fan at the flue gas outlet as long as it has a draft proving switch tied to the gas control. Seal the upper envelope of your home first. Ensure adequate makeup air and consider extending that chimney or better yet raze it and replace with a solid packed insulated stainless steel chimney, which performs better outdoors than B-vent. With that short chimney, your house is probably acting as a better chimney than the masonry one.

Doone

Let me clear up a few things: it is an 8x8 TC flue inside the brick chimney that never had a cap. The 200k btu boiler replaced the old 220 k btu that was there with 12 properly gorton vented radiators. Its a one pipe system with proper Hartford loop and there is no water hammer and no hissing at the valves or vents. New boiler will be skimmed Monday. Its a 3 story brick, 3 family about 145 years old, the exterior brick chimney is 33 feet high and clears the building by 2 1/2 feet. The 12 feet length is the galvanized flue pipe running inside the basement to connect the draft hood to the chimney through the exterior brick wall. It is pitched. The old boiler ran flawlessly for 34 years with this setup. I never get water in from the rain, even when it had no flue cap. No short cycling, it runs to 1 1/2lb c o and 1/2 lb c i from cold start. Plenty of combustion air inside the basement of 8000 cubic feet. The old unit did not have an auto damper, it was always open. I switched the new auto damper above the draft hood off to stay open and now there is no backdraft. The chimney guy will replace cap with a vacu stack tomorrow and put in a clean out access door at the bottom below the flue connection and clean out the chimney which has never been done in 34 years.

Bob Harper

Ok, a few things to consider: Your chimney is a little undersized. The vent connector is right at the min. for your btu input and is ok IF you have 2-3 feet of vent rise from the draft hood to the centerline of the chimney breaching. I hope it is supported every 4-6 feet and at any offsets. The cleanout door must be within 12" below the chimney breaching and not at the floor level. A VacuStack is ok for correcting wind effect and keeping out rain but it isn't magical. Your 8K Cu.ft. will support 160 MBH per the code. It all could be due to a blockage and just needing a sweep but keep in mind terra cotta and Portland cement mortar don't hold up well against flue gases and you will need to install a listed liner soon. Since you have such a huge boiler, you can either install a 6" smooth walled liner and hope it works or bust out flue tiles and install a 7" smooth walled liner or demo. the chimney and install a listed 7" insulated factory chimney or b-vent. Your flue should extend 3ft. above the roof plus 2ft above any point within 10ft. horizontally. The VacuStack is a copout solution for adverse wind effect on short chimneys. Anyway, good luck with it and please advise what your chimney guy finds.

Doone

Thanks for the detailed answer. The new door is within the 12 inches you describe and above floor level, there was no major blockage, however some minor debris came out during the sweep and then the entire bottom was cleaned out of all accumulated debris of which completely filled a sandbag. There is just over 3 feet of vent rise and it has the supports you cite. I think that the vacu stack is taking care of the down draft issues and the spill switch hasn't tripped again. The sweep thought that both the masonry and the liner were in excellent condition for their age. Considering adding a 3 foot extension to the stack after the winter. Thank you for your advice.

Doone

Installed tjerlund d3 flue inducer inline on 7 inch steel duct. Included optional control unit circuit board and fan proving sensor. Nice product that does what its supposed to do and no more spills. Unit reaches initial cutout quicker heats rads and house faster too.

EBEBRATT-Ed

Hard to believe that a chimney 33 feet tall won't pull enough draft but glad you have it fixed

Doone

Thanks.
Only under certain conditions at cold start did the chimney not pull. And as another replier stated it may have been happening for a while under the old system.

A one min purge of the vent line is an adjustable setting included in the controller which prevents any flue gas from being drawn back in by negative pressure or a backdraft after cutoff. The addition of this appliance improved burn efficiency, as well. System now reaches cutout at 37 min instead of 43 min, no other changes or adjustments were made to the boiler

gerry gill

Just out of curiosity, was the old boiler standing pilot and the new boiler spark ignition? second question, did old boiler have a flue damper motor and i assume the new one does.

Doone

Old was a standing pilot, no damper. New one electronic ignition off it's own control board, and motor controlled damper.

gerry gill

I've had a similar problem here and i am conducting an experiment where i just locked open the damper to allow residual boiler heat to keep the chimney warm. So far so good.

Bob Harper

Your system is firing for 37 minutes continuously and that's a good thing? I think you have greater problems. As for the chimney with the cold backdraft, fix the house and the chimney will work. FYI, those "draft inducers" generate positive flue gas pressure. Therefore, the code requires they discharge into venting that is listed for positive vent pressure. That excludes masonry chimneys, 95% of all chimney liners and 100% of all unlisted single walled snaplock vent connector. If there was debris in the base of the chimney that was comprised of masonry such as flue tile chips and mortar then no, your chimney is not in good condition and yes it needs a liner-period.

Doone

> I've just locked open the damper to allow residual boiler heat to keep the chimney warm. So far so good<

Gerry, I tried that too, but regardless, the problem returned in my case. The D3 did what it it's supposed to and problem cleared. Burner flame looks better too. Good luck.

Doone

> @Bob Harper said:
> Your system is firing for 37 minutes continuously and that's a good thing? I think you have greater problems.<

Clarification: that's 37 min from cold start to 1st cut out, after 7 hrs setback of 4 degrees, at 630 am on a 28 degree day in a single pipe 3 story, 12 rad system balanced with properly sized Gortons through out. Then its 3 min on 2 min off after the p trol takes over with about another 15 to 20 min until tstat on 1st fl is satisfied. That's a rise of 4 degrees in the whole brick bldg that's 140 years old. Do you think my setback is too great? Thanks for your input.