Bad Cold Weather "Flue" Season! : (

RickDelta

Motel utility room environment:

2 Laars VW0325CN12CBACX "Mighty Therm" water heaters (325K BTU each unit) w/ 8" exhaust vent ports w/ atmospheric draft only.

1 18" x 18" clay lined vertical chimney (40ft) out thru roof w/ metal cap and open 360 degree bird screen.

Entry into chimney from utility room is a 16" round duct with a 16" side "T" (to connect the second unit)

From there, the pipes are reduced down to 8" flue pipe (left and right) to service the two units.

Both units have internal draft diverters …… but each unit had an external draft duct installed as well.

Hello HeatingHelp Community! : )

I was called in to investigate why the newly installed Carbon Monoxide detectors w/ digital read outs installed in the motel staff laundry area were most of the time reading zero emissions …… then at times going off scale.

The motel just recently installed the detectors because of staff complaints of sick feeling and respiratory issues.

In my troubleshooting, I noticed one of the units had High-Temp tripped out (probably been off line for months)

When the other working unit fired up, it would heat the tank storage water up just fine and then cycle off.

The problem was this unit was spilling all of its flue gasses out the external draft vents! : (

I noticed that even after a few minutes of firing, the large 16" pipe into the chimney was still cold to the touch!

Inspecting the chimney, it was clear of any obstructions.

What I found was that the large volume of very cold air within the vertical chimney effectively blocked any chance of the chimney from developing a natural draft up thru the chimney.

My thoughts to resolve this issue:

Eliminate all the 16" pipe and "T" connection including the external draft hoods, and drop down from the roof two 8" flex chimney vent pipes servicing each unit independently.

……thoughts on this?

Thanks!

SuperTech

Pictures would be great. It really sounds like a lack of combustion supply air. Mechanical room too small? Laundry room? Lots of dryers pulling the area into a negative pressure? My initial thought is to bring in combustion supply air from the outside. A "fan in a can" or something similar. Is the terracotta lining of the chimney in good condition?

Eliminating the draft hoods and installing double acting barometric dampers with spill switches is not a bad idea.

RickDelta

@SuperTech

Hi!

Has two large 3ft x 3ft air supply grills thru to the very large staff work area and this room has a 4ft louvered fan always open to the outside air.

I don't think it would be an air supply issue.

Clay liner looks fine …… I'm thinking the chimney top is exposed to the prevailing winds too much. ….. maybe put on a turn over cap looking the other way??

SuperTech

That wouldn't affect it. The main things that cause bad draft is lack of combustion supply air and poor venting. Plenty of terracotta chimneys out there without any caps work just fine. But if the terracotta liner is in bad shape the chimney won't work properly.

If you have the opportunity please post pictures of the boiler and the flue pipes, as well as the venting for combustion supply air. It's early and I haven't finished my coffee. I'm having a hard time picturing everything based on your description.

RickDelta

@SuperTech

……… thinking:

What if I address both fault possibilities, Install two dedicated 8" insulated vent pipes to each unit and use the remaining chimney volume for a fresh air supply (ie: coaxial venting)

RickDelta

……… mmmmmm re-thinking!

I'm thinking you may have the stronger probility to this issue.

With the 4 commercial dryers running and the exhaust fan running too, Its sucking the flue gasses right out of the small utility room.

Atmospheric venting should never see a competing pressure differential.

RickDelta

…… so, resolve:

Seal (isolate) the two utility room air intake vents from the dryers and outside wall fans in the adjoining room.

Install twin 8" insulated exhaust pipes inside existing chimney (40ft) and use the unused chimney volume for its fresh air intake for the utility room.

….. thoughts on this?

RickDelta

……. down draft problem persists! : (

Today I replaced the typical 360 chimney cap with an turn over style duct cap (see pic) pointed away from the prevailing winds.

This only resulted in a small improvement to the chimney down flow.

so, …… in troubleshooting this further, I shut off all the dryers and large outside wall fan. I closed the door to this laundry room area as well.

Checking the downdraft now, it remained pouring down the chimney into the utility room! : (

The downdraft force is about twice the strength of any upflow firing draft …….. so flue spillage into the utility is almost 100% ! : (

Observation:

When I shut off the powerful outside fan for the tests, after stopping its spin direction, it begins to spin un-powered the opposite way with in a steady counter rotation! ….. the air from the outside is pushing the fan blades in a fairly strong manner. (but, with no real wind outside to speak of). You can feel this same amount of air flow ingress as coming from the chimney draft vent. : (

I'm guessing the with the very cold weather were having, the cold air is creating an overwhelming pressure in thru the chimney and wall fan and not allowing for a normal atmospheric updraft to form.

….. thoughts on this?

RickDelta

………. pondering:

The existing 18" x 18" chimney is feed high (near the ceiling) from the two boilers.

There is an "in the wall" chimney clean-out door at floor level.

I have a main trunk blower fan (from a typical warm air furnace) …… could I not just connect this to the clean-out port to emulate an induced upward draft for this over-sized chimney?

This would surely negate the downward air flow and aspirate (create a negative pressure) to the top of the two exhaust duct hoods

….. thoughts on this?

RickDelta

RickDelta

@EdTheHeaterMan

………. where ya at ED when I need ya? : (