I had planned to do this work myself, but after reading (actually searching, unsuccessfully, for tips) about doing this, I think it’s better left to a professional. I still need some tips to make sure the pro is doing this right.
I would like to vent two water heaters in the same chimney flue (lined, of course.) The original plan was to vent a second water heater in this flue and leave the first water heater where it was. (The space where the first WH now stands isn’t big enough for both, but the new space is. It makes sense to have them together for plumbing purposes.)
My question is can both WH be vented in the same flue? Old WH is only 40 gal, 4 years old, and is doing well. New WH is 50 gal. Both are less than 60″ tall. The opening for the vent is at 72″ on center. Flue is big enough for a 6″ round liner. Instructions for both call for a 3″ vent. (I know a 6″ pipe carries four times as much liquid as a 3″ pipe, but I don’t know if the same holds true for gas exhaust, or if it’s too big. I don’t want the exhaust to cool too much and not rise.) The rise between where the vents would enter the chimney and the top of the chimney would be between 16 and 20 feet. Any gotchas I need to have in mind when I compare bids?
Replies
Welcome to Breaktime!
If both GWH's are gravity vented, then venting the two together is a common and acceptable practice. If one or both are draft-induced (i.e. power vented) they must be vented separately. The size of the common vent will be based on the the rise, the total equivalent length of the vent piping and the total capacity required in BTU/hr. The water storage capacity is not important (for the proper flue selection), but the rated gas input is.
Hart & Cooley http://www.hartandcooley.com/vent/all_vent.htm has a Vent/Chimeny sizing and application guide on their website that is very explicit on the details. I recommend that you download and read this document. It will provide more pertinent information on venting than most professionals can provide.
Thank you Tim!
I have two water heaters, gravity vented. Can they be vented out of a wall or does it have to go out the roof?
Without approved after market draft fans, they have to go through the roof.
Fighting Ignorance since 1967
It's taking way longer than we thought
There are also water heaters that are designed for direct venting. They are sealed and use a coaxial vent that also brings in combustion air.If you are in the market for a new WH.Also you will need to check the specs about separation between the two terminations.
Good point: there are actually 3 basic types of nat gas water heater.Atmospheric (or gravity) draft - the most common (in my area);Draft assisted, which use internal combustion air and a draft fan which mixes a lot of air in with the flue gases so they can be vented through a sidewall (2nd most common,) and the direct vent you mentioned, which have sealed combustion chambers and draw combustion air from outside. (I mainly see direct vent in manufactured housing)See, e.g., Nat draft: http://www.bradfordwhite.com/products2.asp?id=1&product_id=1Side vent: http://www.bradfordwhite.com/products2.asp?id=1&product_id=4And direct vent: http://www.bradfordwhite.com/products2.asp?id=1&product_id=7The direct vent have limited flue lengths - the one pictured is something like 8'
Fighting Ignorance since 1967
It's taking way longer than we thought
Two water heaters? Thats like two wives or two mortgages.I think you are a very strong candidate for tankless. I got one three years ago, been saving 25% on energy costs and have endless hot water. It is the size of suitcase.Regards, Scooter"I may be drunk, but you're crazy, and I'll be sober tomorrow." WC Fields, "Its a Gift" 1934
I run two 40 gal. heaters in series. It gives you a more constant output temperature, since you're drawing from a tank that is replenished at only about 10 degrees below its own temperature.
-- J.S.
You'll save a bucket of money with tankless. It is not burning gas for the 23 hours 30 minutes a day that your're not using hot water. Average savings is 30-50% over tank types, even with blankets.Most have warranties which are at least double, and sometimes triple that of a tanked heater. At $3-400 per heater and with two of them, you'll go 4 water heaters and I'll still be under warranty with my tankless.They won't tip over during an earthquake.Each hot water location can be remotely set up to provide different temperatures of hot water. Kids bathroom set at 100 degrees, Jacuzzi set at 120 degrees, etc.There is zero maintenance on tankless, nothing to drain.Regards, Scooter"I may be drunk, but you're crazy, and I'll be sober tomorrow." WC Fields, "Its a Gift" 1934
Edited 9/7/2006 8:16 pm ET by Scooter1
>>You'll save a bucket of money with tankless. It is not burning gas for the 23 hours 30 minutes a day that your're not using hot water.Neither do tank type.And the savinbgs claimed have been contested:http://tinyurl.com/4elok
Fighting Ignorance since 1967
It's taking way longer than we thought
I can tell you that we have saved about 25%. This is not an opinion, but fact. I pulled gas bills in May through August and compared them to this year and the savings is 25%. Less than advertised, but certainly significant. But, hey, if you like utility companies, thats none of my business. I don't want to give them anymore than I have to.I find it amusing from the article you cited that he says while you do save engergy costs (thats admitted), because it is endless hot water, you use more, so it wipes out savings. Follow that logic and get only a 20 gal water heater--just think of the savings!!!!Regards, Scooter"I may be drunk, but you're crazy, and I'll be sober tomorrow." WC Fields, "Its a Gift" 1934
Edited 9/8/2006 11:01 am ET by Scooter1
>>I can tell you that we have saved about 25%. This is not an opinion, but fact. I pulled gas bills in May through August and compared them to this year and the savings is 25%How old was the water heater you replaced and how much scale did it have?Per the manufacturers, a 1/2" of scale build up in the bottom of a water heater increases gas consumption by 70%In my area, maintenance of 10 -15 minutes a year flushing water off of the bottom of the tank prevents scale build up.And how much did you pay for your water heater(s)A 40 gal nat draft in my area costs about $250 - my understanding is that the tankless with the same delivery capacities cost >1000.So how long does it take the supposed savings to pay for the increased investment cost>I'm not arguing for one side or the other, simply noting that there are two views, and that factors such as age and maintenance have to be taken into consideration.
Fighting Ignorance since 1967
It's taking way longer than we thought
To answer your questions, in my area, tank water heaters last about 4-5 years. My water heaters have a 24 to 36 month warranty, and even the ones that are 60 months, pro-rate the expense, so the warranty is fairly useless after a year or two. The life can be extended by twice a year draining and flushing to about 6 years, or by filtering the water supply with an expensive system I don't maintain them, and don't care to--nor do I care to buy an expensive filtering system. I think it is a pain in the a s s, and don't have a floor drain to do so, so it is a real mess to flush the things. One of the water heaters we pulled out was 2 years old and another was at the end. I don't think there is ANY dispute that tankless save money, the issue is how much.My math was this: I save about $10-15 a month in utilities cost, based on a 2 year comparison. That number is net.With a 4 year life span of a $400 water heater, plus $150-200 delivery, setup, and disposal charge, the water heaters cost me $600 a pop, plus an extra $720 in fuel--a total net cost of $1,920 for hot water for the 4 year period. I had two tanks. My tankless has a 20 year FREE REPLACEMENT, not pro-rated, warranty, and cost me $2,000 plus $200 for installation. No delivery charge, as it weighs only about 40 lbs. There is no maintenance whatsoever, unless you want to dust off the heat exchanger. So in the course of that 20 years, I will spend $15,360 in hot water with the two tanks compared to $2,200 for tankless. That assumes a constant price for fuel, which is not the case. I suspect that the savings will be even greater with increased fuel costs.That was my math, and so far the savings was not what I expected (they claimed 50%), but nevertheless they have been quite significant. If one is staying in the home over 4-8 years, the tankless will pay for itself, and I believe would enhance the value of the home if you are selling it.And, each hot water fixture can be programed to deliver hot water at a specific temperature, so kids rooms have a lower temperature than an adult shower, which is really frigging cool, I think. I have a keypad over the faucet which allows me to pick the EXACT temperature I want to come out of that faucet, and another keypad for other locations as well.Yes, the savings would be less if I bought a reverse osmosis filter, and flushed out the units, but even at a 6 year life span, tankless smokes tank types.Regards, Scooter"I may be drunk, but you're crazy, and I'll be sober tomorrow." WC Fields, "Its a Gift" 1934
Edited 9/8/2006 11:54 am ET by Scooter1
>>in my area, tank water heaters last about 4-5 years. Ahh, gig difference there; 15+/- in my area (for municiple water) a lot shorter for well water - becasue of (i) chemical effects on the tank and significant scale buildup in the tanks (which drives up the energy costs.Why such short life in your area?To me, 10-15 minutes a year running a garden hose and flushing 15 - 20 gallons is far from onerous: not nearly as difficult as writing a check that big <G>>>So in the course of that 20 years, I will spend $15,360 in hot water with the two tanks compared to $2,200 for tankless.You might want to check those calcs, I think you're using the aggegate 4 year fule cost and then multiplying it by the 20 year period, not the 4 cycles.
Fighting Ignorance since 1967
It's taking way longer than we thought
Its 8 cycles--I have 2 tanks, so the total number of tanks in a 20 year period would 8. We got 8 years out of 1 tank, 4 out of another, and 4 and 5 out of others, so it is really hit and miss. I really have no idea why they fail, and really got sick of the whole show.Regards, Scooter"I may be drunk, but you're crazy, and I'll be sober tomorrow." WC Fields, "Its a Gift" 1934
Edited 9/8/2006 1:11 pm ET by Scooter1
Just one thing to add.
The WH's must be on the same floor, & that chimney can't have any other flue connected to it from a different floor.
"I'm here to chew bubble gum & kick azz, & I'm all out of bubble gum" Rowdy Roddy Piper