Thread: Fireplace with Shared B Vent

I recently encounter a fireplace installation in a home built in 1983 that was not finished. The fireplace and vent were there, but no gas line or gas log unit. The fireplace was vented using B Vent. My question is that the fireplace shared the B vent with the water heater, in the same way a a furnace would share the vent with a water heater. In this area, we see VERY FEW fireplace using B vent, and don't think I have ever seen one share the vent with another appliance. Is such a fireplace allowed to share a vent with another gas burning appliance? If it helps, the fireplace was a Heatilator, Model RF36A00. I was unable to locate the fireplace installation instructions.

If it's a wood burning FP it should not be on a B-vent and certainly not share a vent with anything else.

Yes, I understand that. I believe this fireplace was intended for a gas log unit.

I doubt that any pre-fab fireplace is designed to use a shared chimney or venting system.

Originally Posted by Andrew Kolar

Yes, I understand that. I believe this fireplace was intended for a gas log unit.

Gas log units need to be installed into wood burning fireplaces. B-vent is not an option.

Originally Posted by lou curley

Gas log units need to be installed into wood burning fireplaces. B-vent is not an option.

This is a woodburning factory built fireplace that must have the proper listed chimney installed per HTL. It is so old, it's manual is not available for download off the dealer website so I cannot advise if it is approved for installation of gas logs or a gas log lighter pipe or not. I can assure you NO Heatilator or Heat&Glo woodburner has ever been tested or listed for use with ventfree gas logs. Also, VF are not approved with any factory built fireplace prior to April 1999.

If all you see is B-vent, call it out for a level III (3) invasive inspection as their is something major wrong. If you are sure the fireplace is vented with B-vent and that B-vent is common vented with another combustion appliance I would be red tagging and disabling all connected appliances and calling the fire marshal as this is an extreme hazard both for fire and carbon monoxide. Can you publish some pics?

THANK YOU for the information. I don't have any photos of the fireplace vent handy, but it was definitely B vent and definitely shared with the water heater. When I couldn't find the manufacturer's information and based on the B vent, I just assumed the fireplace was a pre-fab fireplace intended to ONLY be used with gas. WRONG!

Bob, where did you find the service parts document you attached?

After speaking with one of the realtors some more, I found out that the homeowner did hire someone to install this fireplace and they had 1 wood fire. The house filled with smoke so fast that it was never used again. The installer was sued and nothing was ever done with the fireplace.

Originally Posted by Andrew Kolar

THANK YOU for the information. I don't have any photos of the fireplace vent handy, but it was definitely B vent and definitely shared with the water heater. When I couldn't find the manufacturer's information and based on the B vent, I just assumed the fireplace was a pre-fab fireplace intended to ONLY be used with gas. WRONG!

Bob, where did you find the service parts document you attached?

After speaking with one of the realtors some more, I found out that the homeowner did hire someone to install this fireplace and they had 1 wood fire. The house filled with smoke so fast that it was never used again. The installer was sued and nothing was ever done with the fireplace.

I got that cut and pasted off the dealer's website with top secret access.

I was asking so that I may have better luck when searching for similar documents in the future. I see where there are Install Manuals, Owners Manuals, inserts, gas logs, blowers, etc. and EVEN Service Parts on the Heatilator website. There is no "search" function, and I didn't see this model # listed in any of the drop downs. I had checked there even before making the post. Is this something I could have had access to, or do you really need "top secret access"? Thanks.

Originally Posted by lou curley

Gas log units need to be installed into wood burning fireplaces. B-vent is not an option.

There are many fireplaces that are ONLY rated for gas logs.

Originally Posted by Jack Feldmann

There are many fireplaces that are ONLY rated for gas logs.

There's a difference between a set of gas logs and a gas fireplace. Gas logs are intended to be installed in either a masonry fireplace or an approved factory built UL 127 listed wood burning fireplace.

Access to "dealer" websites is generally password protected or as I call it "top secret". There would be no reason to host a separate dealer site if it was open to the public. Some mfrs. offer manuals and such on public sites and many do not. This goes for HVAC, fireplace, plumbing, large appliances, cars, etc.

As Lou said, you cannot ASSume any old open hearth fireplace is approved for gas logs. There are built-in gas appliances we call "fireplaces". Some are direct vent, some are B-vent and some are ventfree. This is where knowing the UL listings and ANSI std. numbers will sort them out for you. I've posted them here a dozen times. Even though masonry fireplaces don't seem as limited as factory built woodburning fireplaces, they, too have their limits. First, most gas appliance mfr.s will approve installation of their product only in a code approved fireplace, of which there are virtually none. We can almost always find some defect. Others simply state it must be "working", which means it didn't burn the house down the last time you used it. Now, with VF, you also must look to clearances to the mantel. Often, you'll have to install a big ugly 4" hood or canopy to protect a combustible mantel.

With UL127 factory built fireplaces, not all are approved with vented gas logs. If there is no gas knockout provided, its not approved. Any factory built constructed prior to April 1999 cannot accept VF logs because that's when they were first capable of being listed for VF and not all are.

Learn these std. numbers, document those rating plates and make proper reports on the suitability of a fireplace or appliance.

Originally Posted by Bob Harper

Access to "dealer" websites is generally password protected or as I call it "top secret". There would be no reason to host a separate dealer site if it was open to the public. Some mfrs. offer manuals and such on public sites and many do not. This goes for HVAC, fireplace, plumbing, large appliances, cars, etc.

As Lou said, you cannot ASSume any old open hearth fireplace is approved for gas logs. There are built-in gas appliances we call "fireplaces". Some are direct vent, some are B-vent and some are ventfree. This is where knowing the UL listings and ANSI std. numbers will sort them out for you. I've posted them here a dozen times. Even though masonry fireplaces don't seem as limited as factory built woodburning fireplaces, they, too have their limits. First, most gas appliance mfr.s will approve installation of their product only in a code approved fireplace, of which there are virtually none. We can almost always find some defect. Others simply state it must be "working", which means it didn't burn the house down the last time you used it. Now, with VF, you also must look to clearances to the mantel. Often, you'll have to install a big ugly 4" hood or canopy to protect a combustible mantel.

With UL127 factory built fireplaces, not all are approved with vented gas logs. If there is no gas knockout provided, its not approved. Any factory built constructed prior to April 1999 cannot accept VF logs because that's when they were first capable of being listed for VF and not all are.

Learn these std. numbers, document those rating plates and make proper reports on the suitability of a fireplace or appliance.

Bob; What is the logic in vent free logs not being compatible or listed in vented fireplaces? Is there a known possible failure condition or is it just a manufactures CYA? It helps me to focus and remember if I understand a problem fully.

Thanks

Originally Posted by Vern Heiler

Bob; What is the logic in vent free logs not being compatible or listed in vented fireplaces? Is there a known possible failure condition or is it just a manufactures CYA? It helps me to focus and remember if I understand a problem fully.

Thanks

Certain mfr.s, such as Heatilator/ Heat&Glo designed their units such that the cooling air, which is introduced at the opening of the fireplace into the concentric space around the firebox is discharged into the chimney below the damper. If you close the damper, as you would with a VF, you block the primary cooling system of the fireplace and this WILL result in an unfriendly fire. This is a well documented fire hazard. That's why you must test, pass and list a fireplace with VF so you know to within a reasonable degree of engineering certainty that it will perform within the listing's parameters. Note I did say it was 'safe' because I don't know what that word means except that its an absolute term and NOTHING I know of is 100% safe from any and all hazards, known or unknown.

The listing does give you something to hang your hat on, for sure. If there is an unfriendly fire and the VF was installer per mfrs. instructions and less than 40,000 BTU/hr. input rating (as all listed VF are) then if a fire or other failure results, hey, the fireplace mfr. said in writing it was ok to do so the liability transfers to them. Or, at least some of it.

Originally Posted by Bob Harper

Certain mfr.s, such as Heatilator/ Heat&Glo designed their units such that the cooling air, which is introduced at the opening of the fireplace into the concentric space around the firebox is discharged into the chimney below the damper. If you close the damper, as you would with a VF, you block the primary cooling system of the fireplace and this WILL result in an unfriendly fire. This is a well documented fire hazard. That's why you must test, pass and list a fireplace with VF so you know to within a reasonable degree of engineering certainty that it will perform within the listing's parameters. Note I did say it was 'safe' because I don't know what that word means except that its an absolute term and NOTHING I know of is 100% safe from any and all hazards, known or unknown.

The listing does give you something to hang your hat on, for sure. If there is an unfriendly fire and the VF was installer per mfrs. instructions and less than 40,000 BTU/hr. input rating (as all listed VF are) then if a fire or other failure results, hey, the fireplace mfr. said in writing it was ok to do so the liability transfers to them. Or, at least some of it.

Thanks Bob. If I understand this correctly the danger is not in venting a vent free log set, but in having a unvented fire in a vented fireplace?

I am not aware of any manufactured fireplaces that allowed common venting, b-vent or otherwise.

Bob Harper is right on in his comments.

Most unvented gas logs are dual-listed both to the ANSI Z21.11 unvented heater standard (unvented gas logs) and the Z21.6) decorative appliance (vented gas logs) standard.

In the case of a manufactured fireplace that has not been tested for unvented logs (as Heat & Glo and Heatilator are not), then the logs must be installed to the ANSI Z21.60 standard, which includes a permanent damper opening (the damper is either clamped open or removed).

Frankly, the situation may or may not cause a hazard, but since the manufacturer has not tested the fireplace clearances with the damper closed, there is no basis for making a judgment.

There is a reason why some framing standoffs are taller than others.

Tom Parks
NFI Master Hearth Professional

Originally Posted by Tom Parks

I am not aware of any manufactured fireplaces that allowed common venting, b-vent or otherwise.

Bob Harper is right on in his comments.

Most unvented gas logs are dual-listed both to the ANSI Z21.11 unvented heater standard (unvented gas logs) and the Z21.6) decorative appliance (vented gas logs) standard.

In the case of a manufactured fireplace that has not been tested for unvented logs (as Heat & Glo and Heatilator are not), then the logs must be installed to the ANSI Z21.60 standard, which includes a permanent damper opening (the damper is either clamped open or removed).

Frankly, the situation may or may not cause a hazard, but since the manufacturer has not tested the fireplace clearances with the damper closed, there is no basis for making a judgment.

There is a reason why some framing standoffs are taller than others.

Tom Parks
NFI Master Hearth Professional

Thanks Tom. Would it be prudent to call for permanent damper opening regardless of what type of gas logs are installed in all vented fireplaces? Which is what I have been doing. Any liability issues with this?

Andrew,

We have some great resources on this board but when time is critical (such as having to get the report out) and you know the name of the manufacturer just call them. I do that on a regular basis and then make direct reference to the manufacturer when I describe the issue and resolution.

//Rick

Originally Posted by Vern Heiler

Thanks Tom. Would it be prudent to call for permanent damper opening regardless of what type of gas logs are installed in all vented fireplaces? Which is what I have been doing. Any liability issues with this?

Vern, if we are talking about what is and is not legal, then there is no need to call for a damper clamp in a manufactured UL127 wood burning fireplace that has been tested for use with a set of unvented logs. The concern then is the installation manual combustible mantel clearance requirement associated with the unvented gas logs.

Clamping a damper open with ANSI Z21.11 unvented gas logs will prevent heat buildup, but it would defeat the purpose of unvented gas logs, which is to impart heat to the home. If a homeowner wishes to slightly open their damper to reduce the amount of heat coming into the home or to alleviate odor issues, that is their prerogative.

Let's not get into whether or not unvented gas logs are a good idea. This thread is de-railed enough already.

Tom Parks
NFI Master Hearth Professional

I would like to follow Tom's accurate comments further. If you have VF logs installed but open the damper, then they are being operated as "vented"-not VF mode. Therefore, those logs would require the dual listing, which would mean the damper must be wide open when firing.