gas water heaters - power vent vs direct vent

Hey folks
I need a little "Water Heater 101" here.
We may need to replace our gas water heater soon. We have an unusual setup, due to the people who owned the house before us. It's a normal gas fired water heater, but it vents out through the nearby foundation wall. There is an external blower on the outside of the house that turns on with the water heater to suck the exhaust gas out. Odd arrangement, and sometimes the heater goes out and I need to relight the pilot.
Anyway, we may replace it soon with either a power vented unit or a direct vented unit. From reading manufacturer's web sites, I know *how* they difffer. I just don't know the pros and cons of each choice. What's considered "better"? And why?
Thanks in advance!
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Brian wrote:

If you have a power vent on your exhaust now, you will probably continue to need it. The only time that a power vent is used is when it is impossible (or at least extremely difficult or expensive) to direct vent. A direct vent must be almost vertical all the way to the roof. Can you do that from your current water heater?
As far as pros and cons go, direct vent is preferable due to the fact that there are no moving parts to break down or fail. If everything stays in place, then the vent will function. When it is not possible to do this, or if this would put a vent pipe through the center of your bedroom (as an example) then you would go with the power vent.
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Robert Allison
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I see them with a right angle to go out the wall they are against. I believe it has to be a very short exhaust.
Bob
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A direct vent would work if the power is off, while a powered vent unit would shut down.
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wrote:

Not if he wants to vent it out the wall! Greg
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wrote:

A power vent unit has a 110v fan on it that has to prove operation before the gas burner will fire. A direct vent unit (DV) requires no electricity.
It sounds like the OP had neither, just a cobbled together POS.
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Yep! I blew that one! You are correct! Greg
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wrote:

capable of horizontal venting within a limited range. Power vent units can horizontally vent to a greater distancee, usually through properly rated PVC. Atmospheric or conventional venting is what we are all familiar with and requires a vertical stack to function properly.
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A power vented heater has a blower attached to it, simular to what you have now, but all built into one unit. A direct vent heater is very simular to a standard natural draft heater, it differs in that it has "closed" combustion. It draws the combustion air from outside and vents the burnt gases to the outside through a double wall vent. No power vent needed, it works on convection. No electricity needed either! I would go with the direct vent, less to go wrong. I believe a direct vent needs to be set right at the outside wall, the vent is very short. A power vent can run many feet, so this may make a differance in your case. Greg
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Thanks for the replies!
The distance from the center of the water heater to the inside of the foundation wall is only 33 inches, so direct vent would be a good choice? The direct vent draws in the outside air for combustion, right? (well, at least the Bradford White model that I looked at does)
I will definitely call a licensed plumber to do the work, but I just like to understand the issues.
Again, thanks for your help!
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My direct vent doesn't draw outside air. The other thing to consider is, direct vents are pretty loud from outside the house. Don't put it anywhere near your deck, for instance, unless you want to listen to it every time it cycles on.

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Mark, it sounds like you WH is actually a power vented unit.
It can be a little confusing, but a power vent and a direct vent both go out the side of the house. The main difference is the power vent uses a PVC vent and has a fan on top to force the flue gases out. A direct vent has a pipe inside a pipe and has sealed combustion.

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Yep, you're correct. I was thinking "power vent" not "direct vent"
My furnace has a power vent, the wall mounted propane heater in my shop is direct vent -- there's no fan on that one, and it does pull air from outside. Sorry about that.
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I just had a direct-vent installed; a GSW, identical (I think) to a John Wood. Bradford-white makes 'em too. Go to their websites and browse.
My direct-vent has a flexible coaxial stainless(?) steel pipe, outside diameter 6" or 7", that goes out through the house wall just above the sill, between the floor joists, so it definitely exits horizontally. In fact, from the top of the unit, it bends a bit west, runs diagonally a bit, then bends south to get to the wall. Total run is maybe 5'. (The manufacturers have strict rules about this; it's on their websites.) The exhaust is darned hot, far hotter than from my power-vented sealed-combustion boiler. If I had light-coloured vinyl siding I'd expect some discolouration above the vent, but I have dark aluminum siding so I'm not too worried.
Although it draws outside air for combustion, the combustion chamber is not sealed. It is accessible to light the pilot, and it is still a flammable-vapour hazard.
I *believe*, in contrast, that power-vent units may have fully-sealed chambers, slightly higher nominal efficiencies, and way less strict venting options. Of course they require power.
I went direct-vent because I didn't want to depend on electrical power, and I (really) didn't want to put in a flue liner (I replaced an old electric unit).
Chip C Toronto
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