B vent or direct?

[tinkabranc]

What is the difference between B vent and Direct Vent on a gas stove?

We are still debating if we are going to purchase freestanding gas stove since we already have NG in the house or a second pellet stove. Whichever we decide, we are planning to install it on an inside wall and run pipe straight up and out.

One of the gas stoves we are looking at comes with either pipe option.

thanks

 

[Michael6268]

B vent uses room air from the appliance and drafts via the B vent pipe to the outside. Direct vent uses outside air for combustion and vents to the outside usually via a double wall pipe. The inside pipe carries the fresh air in, and the outer wall carries the exhaust out.

 

[tinkabranc]

If they both could be installed up through the roof- sounds like the DV is the
way to go.

thanks for your help

 

[Michael6268]

Yes direct vent can go out through the roof just like a stainless chimney.

 

[webbie]

No down side really to DV. It offers a more balanced flue.....B can have problems like spillage because it uses room air. And, with DV you can still go straight up, or out or even line chimneys.

 

[BrotherBart]

direct vent is more efficient. big i think 60% BV with draft hood or 80% DV . ask for the specs.

Pook please point me to information establishing that B-vent gas stoves are less efficient than direct vent. It just ain't so. Both have steady state efficiencies in the mid to high 80's and A.F.U.E. in the mid 70's.

 

[webbie]

Hmm, I think it is a grey area......

But, BB is correct in that many modern top efficiency units are equal.

But there is a perception that B vent is less efficiency since many "low-end" units used to be B-Vent only (and not room heater or AFUE tested).....

As with other things, we have to update our thinking. Today you have to look at the specific appliance and make certain it has valid ratings.

Ok, a little more research shows the following - DV ARE MORE EFFICIENT.....in general. Note that certain models (look at VC, etc.) have three efficiency ratings - steady state (when burning), AFUE (wall heater/furnace ratings) AND Energuide ratings. The third one, Energuide, is a test standard developed by the Canadian Government to actually mimic how an appliance like a freestanding stove or fireplace actually performs in a normal installation. As such, it is probably the most accurate to use in a cold climate.

The same VC model that hits 80% steady state and 70% AFUE - is only 60% Energuide!

ALL Energyguide units which are over 70% efficient are DV - see enclosed.

So, I would still stick to the fact that, in cold climates, DV will in general outperform. If you are in a very temperate climate, it may not matter as much.

 

[webbie]

As something to add to this thread, it helps to see the folly of folks claiming that Pellet Stoves are 82% or so efficient. I would be extremely surprised if a Pellet Stove tested to Energuide standards came in above 70%.......if they tested them! It is obviously much easier to fine tune a fixed-fuel appliance like a gas stove...than work with the variables in outputs, fuel and other factors (fly ash, etc.) with Pellet Stoves.

Ah, marketing....don't you love it? Folks talk about 80% efficient gas stoves that are actually 60% - as they say, your mileage may vary.

From the Energuide site:
"From a safety and energy efficiency perspective, your best option is a direct-vent fireplace. Outdoor combustion air is drawn directly into the firebox through one pipe, while combustion products are exhausted through another. This has two important benefits. First, no room air is required for combustion, there is no opportunity for heated room air to escape out the vent, so the units are also more energy-efficient. And because direct-vent units have a sealed firebox, they are generally safer."

http://oee.nrcan.gc.ca/equipment/english/page74.cfm?attr=4

 

[BrotherBart]

Ah, marketing....don't you love it? Folks talk about 80% efficient gas stoves that are actually 60% - as they say, your mileage may vary.

Yeah I have to laugh on the marketing thing. Kozy who does not sell BV units anymore now says that they are crap. Jotul who still sells them says they are just as efficient as DV units.

Sounds like efficiency is directly related to what ya got sell at the moment.

 

[webbie]

I tend to side with the Canadian Government stuff - that is pretty much "tough love".
As I said before, if you like in California it may not matter, but at temps below freezing...well, if I were buying a DV these days, I would look hard at the Energuide DB. They, unlike the stove companies, have nothing to sell (except the truth, some beer and some cold breezes).....