Water heater vent near wall- fan assisted draft

[JPLomeo]

Hi All,

Need some suggestions on this one. Saw a gas fired water heater vent on a flat roof today that was too close to a parapet wall. Looked like a regular B vent and I would typically write that up. When I got to the water heater, it had a fan assisted draft system with no open draft hood.

Being that the termination is just a regular B type vent, do the usual rules still apply- two feet higher than any wall within 8 feet ? The rules for forced air draft systems do not seem to address vertical walls near the vent termination. I would think that a strong wind coming off that parapet wall top would still create a vortex and mess with the draft, fan or no fan.

Thanks

JP

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[mjr6550]

There is no 2 foot within 8 foot rule. 2/10 for chimneys. B-vents have different requirements. Also, fan assisted water heaters have requirements specified by the manufacturer. I have never seen one vented to a B-vent and never saw instructions that specified venting to a B-vent.

[JPLomeo]

Hi,

Thanks for the reply but, yes there is a rule: B or L vent termination within 8 feet of a wall or roof obstruction must be 2 feet higher (per IRC 2427.6.4 and UMC 802.6.2-thanks to "Code check"). Here in AZ we have lots of flat roofs with parapets and often find an incorrect installation.

What's got me stumped is that this has a forced draft fan into a B vent and that's not typical.

I've got to send the report out tonight and I'm sticking with my opinion that this is not quite right. I'll have to defer to a licensed plumber to evaluate and repair :-C

[Marc]

...What's got me stumped is that this has a forced draft fan into a B vent and that's not typical...

Maybe because it isn't supposed to be a B vent. Manufacturer's installation specs trumps Code.

Marc

[inspector57]

Just because it has a fan assist does not change the type of vent, it is still technically not a positive pressure vent such as you would have with a unit using PVC.

Various gas-fired appliances, which are required to be vented, are categorized for the purpose of vent selection into four categories (Categories I, II, III, and IV), based on their vent static pressure (non-positive or positive) and whether the vent gas conditions avoids or may cause excessive condensate production in the vent.

http://ul.com/wp-content/uploads/2014/0 ... liance.pdf

IF it correctly uses b vent pipe, then it falls under the b vent rules unless the manufacturer stipulates a more restrictive rule in their installation manual.

[mjr6550]

Hi,

Thanks for the reply but, yes there is a rule: B or L vent termination within 8 feet of a wall or roof obstruction must be 2 feet higher (per IRC 2427.6.4 and UMC 802.6.2-thanks to "Code check"). Here in AZ we have lots of flat roofs with parapets and often find an incorrect installation.

What's got me stumped is that this has a forced draft fan into a B vent and that's not typical.

I've got to send the report out tonight and I'm sticking with my opinion that this is not quite right. I'll have to defer to a licensed plumber to evaluate and repair :-C

You are correct where there is a wall within 8 feet. I really never see that case since almost every B-vent I see is in a sloped roof, where the height is based upon roof slope.

Unlike fan assisted furnaces that still rely on chimney draft, all of the fan assisted water heaters I see are positive pressure and should not vent to a B-vent.

[inspector57]

Here is one from Rheem that is induced draft rated for use with b-vent.http://www.rheem.com/product/residentia ... uced-draft

Bottom line is you have to check out the instructions to be sure they used the correct vent pipe.

[mjr6550]

Here is one from Rheem that is induced draft rated for use with b-vent.http://www.rheem.com/product/residentia ... uced-draft

Bottom line is you have to check out the instructions to be sure they used the correct vent pipe.

That's a new one for me.

[Marc]

I guess 'B' vents are allowed on induced draft appliances as long as they're not condensing types.

In all my years as a contractor and now as HI, I've only seen one condensing appliance with my own eyes.

Marc

[inspector57]

I guess 'B' vents are allowed on induced draft appliances as long as they're not condensing types.

In all my years as a contractor and now as HI, I've only seen one condensing appliance with my own eyes.

Marc

The farther north you are, the more popular condensing furnaces become.

Marc, I guess you are even more of a cooling climate than me and I rarely see condensing furnaces except on very upscale homes.

[kurt]

Here is one from Rheem that is induced draft rated for use with b-vent.http://www.rheem.com/product/residentia ... uced-draft.

That's a very interesting water heater. 29 gallon/90 gallon FHR with 61 GPH @ 90 deg rise. <18" diameter. That's some serious performance in a tiny package. And, it's rated potable and space heating.

Wow.

[mjr6550]

Here is one from Rheem that is induced draft rated for use with b-vent.http://www.rheem.com/product/residentia ... uced-draft.

That's a very interesting water heater. 29 gallon/90 gallon FHR with 61 GPH @ 90 deg rise. <18" diameter. That's some serious performance in a tiny package. And, it's rated potable and space heating.

Wow.

These are relatively new and pretty expensive, but you get good efficiency without some of the problems of tankless water heaters. I have read some complaints that incoming cold water can dilute the tank temperature and give you less hot water than the specs claim. I talked a neighbor into buying one instead of a 75 gallon with a typical recovery rate. I never get around to asking how they like it (they still talk to me though).

[kurt]

I'm very curious as to consumer experience. I don't particularly like on demand water heaters for a number of reasons. These might be just right.

Also, they'll beat the >50 gallon capacity efficiency requirement that would just plain be a PITA. And, they're small to fit into condo closets.

I'm curious. Anyone finds out anything, I'd like to know.

$848.50 from Amazon with free Prime shipping. It's getting more attractive by the minute.