I’m working on installing a water heater and I have a question about venting.
It has a 3″ vent that extends horizontally 4′ over to an insulated (double wall ) 6″ vertical vent that goes up two stories and out the roof.
The new furnace uses PVC pipes so it no longer uses this 6″ vent. Only the water heater uses it.
How much pitch do I need for the 4′ going over to the 6″ vent. I’d like to get the water heater as high as I can.
Replies
More important than the pitch of the horizontal is the initial vertical height of the vent connector as it rises straight off the draft hood of the water heater.
More important than either one of those is the total height of the 6" vent: the more total height, the better the draw.
Gravity vents like this are designed to operate at a negative pressure; the 6" vent is sort of like a big vacuum tube that "sucks" air/flue gases from its lower end, i.e., the draft hood of the water heater. (What's really happening, for the purists who might read this, is that the heavier, denser air in the space where the water heater is located, is actually pushing a mixture of air and flue gas up and out of the house into the outside atmosphere that is lighter than the inside air.)
Regardless of all that, a simple match test can show you how much draw the 6" has. If the vent sucks up the smoke from a blown-out match, you've got good draft, and it will draft whether the horizontal portion of the vent connector has pitch or not.
The only real purpose of the pitch on the horizontal portion of the vent connector is to drain back any condensation toward the draft hood. It has very little, if anything, to do with proper draft of the vent system.
Simpson DuraVent puts out a really GREAT (and free) publication on venting of gravity vent appliances using type B vent systems, such as are used for water heaters, unit heaters, some gas fireplaces, etc. You can probably find it on their Website also, but the supplier where you buy Type B vent should have it too. It is an excellent education in itself, and it also contains all the vent tables that are in the Fuel Gas Codes.
Thank you. I'll try the match trick and see if it draws. I'm pretty sure it does.
One further caution to keep in mind with every gravity vent water heater when it's located in a room with a forced-air furnace.
I can't tell you how many times I have seen cases where, when the furnace room door is closed, the operation of the furnace actually de-pressurizes the furnace room enough to backdraft the water heater. The water heater mistakenly gets blamed, or, when somebody tests the WH for proper draft, they do it with furnace room door open, and/or the furnace blower not running, and everything seems OK, but it's not.
The test is simple: Close all the windows and doors in the house, turn on the furnace blower, shut the door to the furnace room, and THEN do the match test. To make it a "worst-case", also run any exhaust fans in the house.
If the WH vent backdrafts then, but not when the furnace blower is off, there is a problem with the duct system air balance, and there is a very real danger of CO poisoning. Sometimes it's low-level, and nobody in the house realizes what's going on.
I was going to run through all the scenarios with the match trick. My primary concern is the clothes dryer in the room. I'll see what happens and then decide if I need makup air.
My furnace gets it's air via a PVC pipe.
"My furnace gets it's air via a PVC pipe. "
As you know, the PVC pipe supplies combustion air.
My comments about the furnace are not because of a concern about the combustion air that the furnace uses; the depressurization that can backdraft the water heater would be from the duct system causing pressure imbalances in the house, which, if they exist, are nearly always the worst in the furnace room.
The test I described can be done without even having the furnace burner on--the main thing is to have the furnace blower, or air handler, running, and the door to the furnace room or space closed.
And your concerns about the dryer possibly de-pressurizing the space are right on.
If I sound a little paranoid about furnace room de-pressurization, well..., I am. I have seen many cases where it was happening, and several where whole families ended up in the hospital. Probably your house is fine, but doing a couple of simple tests can confirm this.
Thank you. I'll do the test and see."There are three kinds of men: The one that learns by reading, the few who learn by observation and the rest of them have to pee on the electric fence for themselves."Will Rogers
The water heater has a draft diverter on top, when it is slopped enough, it will draw a match flame towards it.
If you turn on the dryer, it will suck air down the vent pipe and the water heaters combustion products will be sucked towards the dryer.
I would recommend that you consult a professional for this particular project. No offense, but some of the exchanges I've read here would indicate that you shouldn't do this. I am usually a proponent of DIY and learning new things, but venting combustion gases out of your home (or anyone else's) is not a project you want to get wrong. You will not get a second chance.
Thanks for recommendation. I'm not sure what to say Tim. If I try to defend myself I just prove your point in a way. But if I don't respond i feel I have left you with a mistaken assumption.
Above all else, I want to treat people with courtesy and kindness if at all possible.
But sometimes when you do that people mistake it for ignorance or plain old stupid.
I just don't know what to say. Maybe if you lived close by we could sit down and talk about it. But over this forum it's hard to know who anyone is or where they are coming from.
Oh, I can get an idea. But I might be wayyy off, so I try not to or if I do I keep it to myself.
"There are three kinds of men: The one that learns by reading, the few who learn by observation and the rest of them have to pee on the electric fence for themselves."Will Rogers
Tim
Getting professional advice is very hard to do. Here in Southern California, the so called experts are out to get your money. Hardly anyone repairs anything with a simple part, they want thousands for a whole new thing and thousands to install. Name a Company who cares more about reputation than the almighty dollar.
The local Gas Company use to train really well, but the old time gas employees say it is no longer done. They use to fix pilot lights, but not anymore.
Learn how to take digital picture and upload, we can help you a lot more.
Make sure the flame of the water heater is blue with no yellow AND get a C.O. detector to make sure your installation is safe.
Thanks for the idea. a C.O. detector isn't a bad idea."There are three kinds of men: The one that learns by reading, the few who learn by observation and the rest of them have to pee on the electric fence for themselves."Will Rogers
"Here in Southern California, the so called experts are out to get your money."
That is an unfortunate reality for all areas of the country, not just SoCal. When I was in a "blended sales" position (when I wasn't designing systems, I was making/taking orders) at a company that sold, amongst a large assortment of HVAC and plumbing products, venting materials, I sold and/or recommend to people only what they needed to do the job. My thought was that a satisfied customer that trusted you, for good reason, would always come back and generate a consistent stream of business far outweighing the small upsale profit from taking advantage. I'm frequently in the minority, but I don't mind.
Go for it. You'll do just fine. (As you know already.) It's the guys who don't ask questions that get in trouble.
Or, like the old country boy said: "Ain't what you don't know what gets you in trouble..., it's what you know fo' sho'--what ain't so."
I would recommend, if you are going to run atmospheric venting, get a good reference in sizing the vent. One of the best readily available is found on Hart & Cooley's website. Rise, run and btu rating of the appliance are needed to properly size a b-vent system.
Sometimes the terminolgy and the presumed nature of a question posted leads one to believe the OP has plenty of knowhow, generally, but possibly no familiarity with the issue at hand. As I said before, I am very much in favor of DIY. But, there are limits. Personally, I would rather been perceived as a "phallus" recommending someone not attempt specific projects out of their range of knowledge and familiarity, than to indirectly or directly be party to creatin of a potentially lethal mistake. Err on the side of caution, right. Not to be taken as a criticism, but possibly a reality. No offense intended.