Vent cap required for gas boiler vent?

lbeachmike

Seven weeks ago the top of our chimney was reconfigured to install a lock-top damper for our fireplace. The old furnace vent cap was removed. Below are before/after photos.

A few days later, during an extremely windy day, the boiler spill switch tripped. It has not tripped again since, and it never before tripped during the five years we've lived here.

Is a vent cap required?

EBEBRATT-Ed

@lbeachmike

Lets see if I got this. You have a two flue chimney. 1 for the boiler and 1 for the fire place. You remove the cap from the boiler flue, put on a top of the flue damper for the fireplace and then put a cap that covers both flues.

IMHO
if it's an 80% boiler no cap is required but you could have the issue you had. If it is a 90% boiler the exhaust would have to penetrate the top cap.

You might have to have your boiler flue raised to penetrate the new cap and then put a new cap back on.


Best bet if the problem persists is a chimney liner for the boiler extended through the new cap with a cap on it

lbeachmike

EBEBRATT-Ed said:

@lbeachmike
Best bet if the problem persists is a chimney liner for the boiler extended through the new cap with a cap on it

How did I not even think of that? I've never noticed that done before - sounds like it would be sort of custom. What about a small cap inside that cage under the new cap?

How do I know if I have an 80% or 90% boiler?

I don't want to find out the hard way if the problem persists. Any scientific way to know what is required to not have another problem?

EBEBRATT-Ed

No, a cap under that cap is not allowed. No way to know if it will happen again.....but Murphy's law says it might.

You probably have an 80% boiler. Post a picture

You would have to install a chimney liner down the flue to the boiler up through the chimney and through the new cap by cutting a hole in it.

or

Put on a smaller cap to just cover the fire place flue but the 2 flue tiles close together may not allow this

post a picture of your boiler & flue pipe so we can see

lbeachmike

I will post pics of the boiler and flue pipe tomorrow.

The work that was done was what the chimney guys came up with, so I'll want to understand if there is anything improper about it that would warrant me asking them to make changes without added expense?

When I look around at neighboring houses, all of them appear to be done this way.

Bob Harper

The 1777 listing for liners requires some sort of rain cap. It does not prohibit unlisted caps. NFPA 211 does not require caps but specifies the net free area and discharge clearance of 5", which this cap seems to meet.
It is common and growingly accepted practice to install one large multi-flue cap whose lid covers the entire crown. This cap does not protect that mortar crown, which will fail soon. You should have a cast concrete crown that overhangs 2" per side sloping 10degrees with a bond break to the flue tiles, a drainage plane with weep holes under it and preferably a single cap whose lid overhangs the crown, so the actual drip line is about 4-5" from the face of the chimney. This chimney has a reverse corbel at the top, which explains some of why it also needs to be pointed. Use lime mortar and not Ordinary Portland Cement-based mortar. OPC traps moisture while lime dries quickly. Lime is softer and won't damage the bricks.
Does the fireplace have a listed liner or just TC tile? Please post more pics of boiler vent connectors and rating plate.
That cap appears to be mortared into place. A proper multi-flue cap either mounts using a screw down flange onto the crown or better, an outside mount secured from the side.

lbeachmike

Why will the crown fail "soon?" The chimney company just added that crown with the new fireplace lock top damper as well as the new vent cap and cage. This is certainly not my area of expertise, so I did not realize there was a reason to question what they were doing. The work came with a 10-year warranty. As a consumer in my area, it's nearly impossible to find contractors that will do things to the level of thoughtfulness that you articulate. I simply don't know how to find that level of expertise around here, now matter how much you're willing to pay for quality.

EBEBRATT-Ed

@lbeachmike

I don't think they did anything wrong. The question really is will you have a wind issue now that the boiler does not have a dedicated chimney cap.

If you have the issue again call the chimney people and discuss it with them. Maybe they can come up with a fix

lbeachmike

They said they were going to add a vent cap inside that cage with the larger cap, but they never returned to follow-up, and on this thread I think you said that is not legal (nor do I think it will even fit.)

Bob added some comments about the integrity of the crown itself.

Re: wind issue - Is there are wind issues that don't get to the point of tripping the spill switch, doesn't it still create a concern of some level of CO going back into the house? For example, if there are intermittent gusts, the gusts may not trip the spill, but they could cause intermittent backdraft, right?

lbeachmike

Sorry for the delayed follow-up. Below are the photos of my boiler and ratings plate. Does this provide enough info on whether a dedicated vent cap is required?

Larry Weingarten

Hi @lbeachmike ,It's way off topic, but the relief valve on the water heater is too far above the tank to be of much use. Unless that valve has an extended probe, it's not sensing actual tank temperature and is a safety concern.

Yours, Larry

lbeachmike

Larry Weingarten said:

Hi @lbeachmike ,It's way off topic, but the relief valve on the water heater is too far above the tank to be of much use. Unless that valve has an extended probe, it's not sensing actual tank temperature and is a safety concern.

Yours, Larry

Thanks Larry. How would I know if it has an extended probe? What specifically would be a problem scenario? If there is too much pressure, it potentially won't relieve the extra pressure? How do I confirm whether it is a problem?

Any insight on the topic at hand re: vent cap requirement? That could be a bigger safety concern if CO is coming back into my house and I end up too brain-damaged to deal with the problem you point out

Bob Harper

The crown was rebuilt as a 'crown wash' using Ordinary Portland Cement (OPC)- based mortar. Mortar is designed to bond and separate individual masonry units. It is not intended nor designed to be a monolithic casting in direct exposure to the harshest conditions of weather, wind, sun, and erosion. That's why brick intended so such outdoor use must be SW or Severe Weather grade.

The IRC dictates a crown be cast of min. 4" concrete with a minimum 2" overhang with a drip edge a min. 1.5" from the face of the brick. It must slope 10 degrees, which is about 2"/ LF. It must have a resilient bond break to the flue tiles to allow for thermal expansion. It must be flashed to the top course of brick with weep holes to provide drainage. Weep holes directly below the bond break and at the base of the wythe wall are required to depressurize the interstitial space between the outer wythe and the flue tile (0.5-4" air space). The flashing must be a 'pan' or 'through-flashing'. This means it must be visible below the crown with a drip edge and extend to then up the flue tile above the concrete. There, a counterflashing must hang like a curtain from over the top edge of the last flue tile down overlapping the pan flashing forming a slip joint to allow for thermal expansion elongation of the tiles.
The concrete must be reinforced with corrosion resistant hardware cloth of 1/4" squares. Rebar is optional and usually ruins crowns when it rusts. This not only acts as reinforcement to hold the crown together but to form a matrix for microscopic air bubbles to attach. This prevents surface bleed where such bubbles rise through the freshly poured concrete leaving microscopic 'chimneys' that provide channels for water to enter, freeze and destroy the concrete. Microscopic air bubbles form little shock absorbing pockets in the cured concrete further strengthening it. The concrete should be air entrained to withstand the effects of freezing rain. That means a type 1A Portland cement.
OPC has a few detrimental properties. First of all, it is hard. Too hard. It will expand more than the surrounding masonry. Where it abuts the flue tile without an expansion joint, it can crack the tile. If the tile was hard-fired forcing the OPC crown to expand towards the perimeter, it will de-bond and lift, thus failing forming a channel for water intrusion. Water will curl into this space rather than drip free due to capillarity. OPC has the property of blocking water vapor transmission. In other words, it tends to trap moisture rather than allow for rapid drying. This means the top of the chimney will rot from moisture attacking the brick, mortar and flue tiles. If it freezes, the water will expand, crack the substrate, flush the crack then repeat with gradually growing cracks. It's an insidious cycle. OPC has a very low modulus of elasticity. It's not a shock absorber in the case of a chimney fire or merely from expansion due to swelling with moisture.
Since there is an improper drip edge, water will run off this crown wash right down the face of the masonry soaking it rather than free-falling to the roof. The reverse corbel will catch that water and channel it into the masonry.
A single large outside mount cap could mitigate many of these defects.
HTH

lbeachmike

Bob Harper said:

A single large outside mount cap could mitigate many of these defects.
HTH

Thanks Bob. I don't know what is meant by the last line of your response. I don't know what this looks like. Is there a photo somewhere of what you suggest?

Also, I am hoping to learn more about the vent cap configuration.

EBEBRATT-Ed

The relief valve if installed incorrectly would relieve on pressure but not on temperature if the temperature probe is not sticking into the water heater as it should be

lbeachmike

EBEBRATT-Ed said:

The relief valve if installed incorrectly would relieve on pressure but not on temperature if the temperature probe is not sticking into the water heater as it should be

Thanks for explaining. How would I confirm whether the probe is sticking into the water heater as it should be?

EBEBRATT-Ed

Your first photo shows a vent cap on what looks to be "b" vent or a chimney liner run down through the chimney. If that is true the boiler must have a dedicated cap and can't be terminated under the large cap that is now in place. You would have to cut a hole in the new cap extend the boiler flue through it and install a cap on the boiler flue & seal the opening where the boiler flue comes through the larger cap.

If that is not true and the boiler flue is in the chimney tile and the old cap and a section of pipe was installed on the flue to prevent wind problems. Then you can leave it as is. But there is no gauarantee that you will not have problems with the wind issue

If you have wind issue problems then install a chimney liner and run it up through the larger cap and terminate it with a cap on the boiler flue

Or replace the boiler with something that can be vented through the side wall

lbeachmike

EBEBRATT-Ed said:

Or replace the boiler with something that can be vented through the side wall

I like this idea if I had limitless budget, but isn't this an expensive remedy for the problem at hand?

I'm still unclear as to how to understand or confirm whether a dedicated vent cap is required. What is the specific criteria?

EBEBRATT-Ed

As I mentioned above. A dedicated vent cap is required if you have a chimney liner or "B" vent run up through the chimney tile liner from the boiler to above the top of the chimney. The liner or "b" vent would be connected to the boiler flue and protrude above the top of the chimney.

If the boiler is vented into the clay tile chimney with no liner it doesn't HAVE to have a vent cap. But a vent cap may solve your wind issue

I can't make it any clearer

Safety is the top priority not the budget

Read the other current post"please please read the instructions"

lbeachmike

Thanks Ed. Thanks for clarifying. My initial confusion was that I was unclear if it was because of what it had previously. I also don't know what a B-vent is. But I think I now understand.

Yes, there is a liner running from the furnace up through the chimney.

Why is a vent cap required if there is a liner and not required if there is no liner?

I am concerned about wind causing backdraft. You mention safety as the priority - is that because of concern for CO coming back into the house when it is windy?

Bob Harper

lbeachmike said:

Bob Harper said:

A single large outside mount cap could mitigate many of these defects.
HTH

Thanks Bob. I don't know what is meant by the last line of your response. I don't know what this looks like. Is there a photo somewhere of what you suggest?

Also, I am hoping to learn more about the vent cap configuration.

Go to chimney caps dot net to see various styles. This is one mfr. but any chimney contractor can get custom caps made similar to these. Check out styles #9-16 for outside mounts with overhanging lids. There are codes that require things then there are just better ideas and Best Practices.

lbeachmike

Thanks for the link, Bob. They have some nice solutions, but I don't see how to solve my issue without a chimney company that knows how to do things properly. I don't think a cap that goes over everything is going to easily allow for a dedicated furnace vent. I will probably need to go back to having two separate vent caps.

It seems like the guys who did the current work made a lot of critical mistakes.

Any suggestions for how to find a highly qualified chimney company?

EBEBRATT-Ed

@lbeachmike

I had a cap at my house that covered both flues. I installed a new boiler that needed a liner. I made a hole in the top of the big cap ran the liner up through it and put a cap on it and sealed around the hole with flashing. Worked fine

I questioned the gas inspector about it and he said I did the right thing. When you have a liner or "B" vent (which is a rigid liner basically) the dedicated cap is part of the liner system and needs to be installed. Without it it's not a complete system


Maybe a certified chimney sweep is who you should call. They install liners at least in my area

lbeachmike

Thanks Ed. We used a licensed and certified chimney company for this work.

I don't think your approach is the best solution for me (the hole through second cap) because that would seem to lead to greater complexity when the chimney is swept. That seems to mean that the next guy has to remove all of that and replace/reseal everything properly, allowing more room for future error. Again, I feel that finding a company with a high level of expertise and integrity will best solve my issue. The knowledge gained here is very helpful in better understanding what is required.

Is there anywhere documented as code or best practices that the dedicated vent cap is required in my circumstance so I can refer to that directly?

EBEBRATT-Ed

You said above that you have a liner installed in the chimney for the boiler. All chimney liners require a dedicated cap. It's common knowledge and section 12:1:3 of the National Fuel gas Code specifies that all chimney liner shall be installed in accordance with the liner mfg instructions.

Since all liners are installed with caps you need a cap.

If the boiler was vented into a chimney with no liner a cap would not be required. Rain snow going down the chimney would fall to the bottom of the chimney and not go into the boiler.

With a liner rain and snow can go down the chimney into the boiler

Having the double cap does not count it's not listed or approved for the liner.

lbeachmike

Thanks for the explanation. I'm not sure what you mean by "having the double cap does not count" ... what double cap?

Re: common knowledge - it seems the common knowledge is as scarce as common sense. I wish there were consumer guides for these types of basic things so that consumers like myself could be adequately informed when having work done, even though it should be on the contractor, not the consumer.

What recourse do I have against the chimney company for not doing things to the National Fuel Gas Code requirements?

EBEBRATT-Ed

@lbeachmike

The new double cap that covers both flues can't be part of venting a liner system.

Call them and see what they say. If the boiler has a liner what they did was not right.

lbeachmike

Ah, I didn't realize that was called a double-cap. Thanks for clarifying.

I don't see how I can remedy this with the current chimney company in any way that would allow me to feel safe and sleep at night. From the things you and others have explained, they didn't get the very basic fundamental things right. They did not value our safety.

From what I learned from this thread - errors include -

1. Heating system vent required a dedicated vent cap per National Fuel Gas Code
2. Double-cap can't be part of venting a liner system
3. Crown has no drip-edge, and the type of mortar used will be a problem over time

My obvious main concerns are #1 and #2. You can't put a price on safety.

EBEBRATT-Ed

Like I said a hole in the big cap run the liner up through that with the proper cap on top. Done. I don't see an issue if the do it right.

If you need access you take the boiler cap off then the top of the big cap. Not hard

lbeachmike

Ed - Are you coming by to do this for me?

Brent H.

Thinking about this, I have a pretty similar setup with a cap that covers both flues. One of the flues has a liner without their listed cap on it. It was done like this when I had the big cap over the flues installed by a sweep years ago. The small liner cap was removed when the big cap was installed but they insured there was 5” of clearance between the top of the liner and the big cap.

Ed, I’m actually not sure how I could use the big cap and also use the liner cap like you mentioned. For the liner I have, the liner is clamped to the plate at the top of the flue. The liner cap is then mounted to this plate, not really to the liner itself. If I extended the liner through the big cap I then couldn’t mount the liner cap as required by the manufacturer. In the end, I’m not sure there is any way to meet the UL listing for the system while using a big cap.

All this being said, I am not concerned about it and don’t believe it is unsafe. It would require severe winds for any snow or rain to make it under the big cap and into the liner. If it did, it would settle in the T at the bottom and evaporate just like condensation from the boiler exhaust.

I don’t think this is an uncommon setup ever though it might not meet mfg. requirements for the system.

EBEBRATT-Ed

What I did right or wrong.

A liner system comes with a cap. To make it an approved venting device the whole thing needs to be installed.

My liner was 4".

I cut a 5" hole in the big cap.

To the bottom of the big cap i attached a 2' section of 5" smoke pipe to act as a sleeve for the liner. The sleeve hangs down in the chimney and protects the liner where it is exposed between the top of the chimney and the bottom of the big cap.

Then on top of the big cap I used the flashing with clamp (that normally goes on top of the chimney) and secured that to the top of the big cap. Brought the liner up through the new sleeve through the big cap, put the big cap in place and put the liner cap on the liner.

I know clear as mud...confused yet?

When I did this I wasn't sure how I was going to do it and thought about putting the dedicated cap under the big cap. But I did it as above. I mentioned it to the gas inspector and he told me "you did the right thing, I wouldn't have approved it without the cap or with the cap under the big cap.

I don't know what else to say

Bob Harper

8 Chimney Caps
8.1 A cap shall be provided to resist the entrance of debris and rain into the flue-gas conveying conduit
of the chimney liner, and into any space where exposed thermal insulation is located. See Rain Test,
Section 36.
Exception: A cap is not required to be provided, when a cap is commercially available that:
a) Has been found to comply with the Rain Test, Section 36, and with the requirements for the
material from which the cap is formed, see 7.5; and
b) The use of such cap is specified in the installation instructions or training manual.
8.2 A cap shall be constructed so that leaves and debris fallen or blown onto it are not retained so as to
obstruct flue-gas or cooling-air passages. A cap shall be constructed to resist the accumulation of soot
that obstructs the flue-gas or cooling-air passages.
8.3 A cap shall be removable and replaceable by the use of simple hand tools (screwdriver, wrench, or
pliers) to allow for chimney cleaning in accordance with the installation and maintenance instructions
without bending or deforming the chimney liner, or parts thereof

36 Rain Test
36.1 The quantity of water entering the flue-gas conduit or any other individual passageway shall not
exceed 2 percent of that which enters the conduit or passageway if unprotected by a cap or other means
when tested as described in 36.2 – 36.6.
36.2 Representative sizes and styles of caps are to be subjected to the tests described in 36.3 – 36.6.
Each cap is to be installed on a chimney section in a manner that sheds the water spray away from the
underside of the cap. The arrangement is to permit any water entering the test assembly from above to
be observed at the underside of the chimney assembly and collected.
36.3 The rain test apparatus is to consist of three spray heads mounted in a water-supply pipe rack
illustrated in Figure 36.1. Spray heads are to be constructed in accordance with the details illustrated in
Figure 36.2. The water pressure for all tests is to be maintained at 5 psig (34.5 kPa) at each spray head.
The spray is to be directed toward the top and side of the cap. The cap is to be centrally located within
the spray pattern and the top of the cap under test is to be at least 3 feet (0.9 m) below the plane of the
lower spray head outlet.

From UL 1777 for liners

8 Caps
8.1 A cap shall be provided to resist the entrance of debris and rain into the flue-gas conveying conduit
and into any cooling-air passage terminating exterior to the building. See Rain Test, Section 27.
8.2 A cap shall be constructed so that leaves and debris falling or blown onto it are not retained so as to
obstruct flue-gas or cooling-air passages.

From UL 441for B-vent

Alternate Chimney Top Terminations for
Forever Flex™ / Pre-Insulated Forever Flex™
The standard chimney top termination for a Forever Flex lining system is the use of a Forever Flex top plate
and cap. However, some installations may require or you may desire an alternative top termination. Other
chimney top terminations are approved as follows.
1- Liner, mortar secured, to crown with any listed rain cap: Insulate liner to within 4” (10cm) of
chimney top. Fill the remaining 4”(10cm) with mortar or crown mix and form a slope from the liner to
the outside edge of the chimney. Attach listed cap to the liner.
2- Liner, mortar secured, to clay flue tile with any listed rain cap: Insulate liner to within 4” (10cm)
of chimney top. If not already existing, slip a full or partial length clay flue tile over the liner. Fill the
gap between the clay flue tile and the chimney with mortar or crown mix and form a slope from the flue
tile to the outside edge of the chimney. Fill the gap between the liner and the flue tile with mortar or
crown mix. Attach listed cap to the liner.
3- Slate Flue Covers: In many residential communities slate flue coverings may be desirable. However,
sufficient protection from precipitation and debris must be ensured. To make certain of this protection
do the following: (1) Determine the distance between the top of the liner and the bottom of the slate
covering, (2) Divide this measurement by 2.5, (3) This number gives you the minimum overhang of the
covering past the edge of the liner. [Example: the covering is 12” (30cm) above the top edge of the
liner. Divide 12” (30cm) by 2.5, which equals 4.8” (12cm). The covering must extend at least 4 ¾”
(12cm) in all directions past the liner opening.] This provides a minimum 22.5 degree angle from liner
edge to covering edge.

Alternate Chimney Top Terminations for ArmorFlex/Hybrid Liner
The standard chimney top termination for a ArmorFlex/Hybrid Liner lining system is the use of a top plate,
clamp, storm collar and cap. However, some installations may require or you may desire an alternative top
termination. Two other chimney top terminations are approved as follows.
1- Use of any listed rain cap: If existing flue tile will protrude a minimum of 1” (2.5cm) above crown,
trim top plate to outside dimensions of flue tile. Silicone top plate to flue tile and secure support clamp
to the liner. Now install a square or rectangle listed cap bolted to the flue tile (Ensure the liner does not
protrude excessively into the cap so as to restrict flow.). If no flue tile is protruding above the crown, use
of a flue tile extension may be needed to secure the cap to the chimney. If installing a round listed cap,
use of a storm collar may be necessary to keep precipitation from going between the liner and top plate.
2- Slate Flue Covers: In many residential communities slate flue coverings may be desirable. However,
sufficient protection from precipitation and debris must be ensured. To make certain of this protection
do the following: (1) Determine the distance between the top of the liner and the bottom of the slate
covering, (2) Divide this measurement by 2.5, (3) This number gives you the minimum overhang of the
covering past the edge of the liner. [Example: the covering is 12” (30cm) above the top edge of the
liner. Divide 12” (30cm) by 2.5, which equals 4.8” (12cm). The covering must extend at least 4 ¾”
(12cm) in all directions past the liner opening.] This provides a minimum 22.5 degree angle from liner
edge to covering edge.

ForeverFlex listed installation instructions. If you call any liner mfr. and show them a large multi-flue cap as I showed they will advise you it's fine as long as it protects the liner and does not obstruct the free flow of flue gases or clog up. I also discussed this directly with Bob Zimmerman at UL before and they don't have a problem with it. However, I will bring it up at our next Standards Technical Panel Meeting in Jan. Meanwhile, this shows there are provisions for caps other than the one the mfr. had tested and listed for their product. They provide 'a' cap- not the only cap.
HTH

lbeachmike

Thanks Bob. So it sounds like my configuration is a proper installation then?