RE: B vent; D vent; ventless and which models??? (Follow-Up #1)
posted by: renron on 12.19.2006 at 07:28 pm in Fireplaces Forum

First, DON'T install a ventless fireplace!!!
Even though the MFG.s will tell you the exhaust fumes are OK, do you really want to breathe them? Many people end up with Major Headaches and chronic breathing issues. Does it sound like a good idea to breathe burnt exhaust gasses?
B type flue(vent) pipes are dual thickness pipes. A pipe inside another pipe, suitable for use at 1" or more to flammable materials. Outer casing pipe is sealed and will not conduct air.
D (Direct Vent) type flue(vent) pipes are also dual layers but they are capable of exhausting burnt gas through the inner pipe and importing exterior(outside) combustion air for burning. Think of a straw inside a larger straw. Inside straw blowing, outside straw sucking outside air for combustion. A fan is usually used to help exhaust the burnt gasses.

Details below:
B-Vent (Natural Vent) gas fireplaces are designed primarily for decorative use. Generally they produce a larger and more realistic yellow flame. B-vent fireplaces are sometimes available without a glass window, so many homeowners are attracted to this design because of the open, realistic flame effect; some models do have a glass window so the existence of a window on a fireplace does not define its product classification. Natural vent gas fireplaces use room air for combustion and vent fumes through a vent or chimney that must terminate vertically above the roof line. The key to determining whether a B-vent fireplace will meet your heating needs is to check the manufacturer's listed efficiency rating (gas consumed x efficiency = heat output). While efficient, heater-rated B-vent fireplaces do exist, many lower quality "builder grade" fireplaces have no efficiency rating and, therefore, will not supply substantial heat. In fact, this category of fireplace will often use the greatest amount of gas at the lowest range of efficiencies. If you live in a warmer climate where you want the aesthetics of a fire without much heat, this may be the appliance for you. Likewise, bedrooms and smaller rooms may be a good candidate for a b-vent fireplace, but please check building codes to see if this class of fireplace is approved in your locality or for installation in the room where you'd like to use it. Local/national codes in some areas prohibit the use of b-vent rated appliances, especially in colder climates. Be aware that very "air tight" houses can cause performance problems with b-vent rated appliances, so please consult an experienced fireplace installer who can advise you on the proper installation and use you are considering.

Direct Vent Fireplaces offer the most features with respect to gas consumption, efficiency ratings and venting options. A direct vent fireplace will always have a glass window because these fireplaces are sealed systems using a double walled venting system. Combustion air enters the appliance via one section of pipe while fumes and moisture are vented through the other pipe. Most often, a double wall "pipe within a pipe" system is used. Subject to each model's requirements for distance and offsets, direct vent fireplace venting may be terminated either horizontally or vertically. Efficiency rating will average 65% to 84%, similar to ratings on gas furnaces. Keep in mind that these appliances must "waste" some of the heat produced to create a draft of rising warm air to evacuate the fumes produced without aid of a forced air exhaust system. Think of direct vent fireplaces as a decorative furnace: the beauty of a realistic flame with high efficiency. This appliance is great for primary or supplental heating and for emergency backup heating as most work without aid of electricity. Because this is a sealed system that uses outside air for combustion, direct vent fireplaces are usually the favored choice among those in the fireplace industry because of their greater efficiency and exceptionally reliable performance.
Hope this info helps,
I am a General Contractor.
Renron

Unvented heaters are 99% efficient, and you can buy a smaller BTU unit for far less than a Direct Vent and get the same amount of heat.

I've been pricing these DV v Unvented. DVs are more expensive and less efficient but offer totally oderless operation.

There is only one DV unit that approaches the efficientcy of a unvented fire, the Mantis, and it is about 95% efficient. Most DV units are only 80% efficient. Think of a DV unit as an inefficient pretty furnace that can be operated for hours and hours without end. Think of a unvented fireplace as a pretty heater that can be operated for 3-5 hours a day with the windows closed.

As for B-Vent fireplaces... totally useless. They draw air from the house and are vented up a chimney. They are totally useless for heat, but make the prettiest flames. In many states you have to leave the flue open 24/7 even when there is no fire. You may have a B-vented fireplace with glass doors. This would be why you don't feel much heat from the current unit.

To me it comes down to cost and odor. If you want the most efficient, low cost solution that offers a pretty and attractive fire, and some risk of unpleseant smell... go unvented.

If you can spend more and don't care so much about efficiency and do care more about the odor and moisture issue, go DV.

In either case get a good CO moniter. You can get a bad seal on a DV fireplace, and since a DV fireplace produces far more CO than an unvented fireplace, the results are instantly bad news.