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Boiler Upgrade Question

mbarrett03 Member Posts: 10
Just moved into a house with a 40 year old gas boiler (oil conversion).  The hot water tank is also gas, but this seems to be only 2 years old.  I want to upgrade the boiler to a new energy efficient model because it already broke once in the 3 months I've owned it, and it's only 65% efficient so a new boiler should save me money. 

I had an estimate given for this work, and the guy told me that if I want to install a new high efficiency boiler it would mean venting the boiler out through side of the house rather than up the flue.  He also said that my existing hot water tank which also vents out the flue would run into venting issues if the boiler vented out the side of the house.  So he quoted me for a new boiler and an indirect water heater.

My question is can I keep the existing hot water tank if I am upgrading the boiler?  The water tank is from 2008 - so it's not that bad.  Just trying to keep my costs down, but I don't want to run into issues with the water tank not venting properly.

Thanks for any help!


  • Tim McElwain
    Tim McElwain Member Posts: 4,560
    You could use the

    existing water heater until it fails and then go indirect. Just have him pipe it up so that can be done as an addition later on.

    Your contractors concern about the existing water heater into the existing flue is legitimate concern with retrofitting to a side wall vent system. Removing the existing boiler may cause the vent with just the water heater installed all by itself into the flue to not be able to draft properly.

    Do you have a masonry chimney or is it a double wall type "B" vent?
  • mbarrett03
    mbarrett03 Member Posts: 10
    Thanks for the reply Tim

    I have a masonry Chimney. 

    What would be a consequences if the water heater didn't draft properly? 

    I like the idea of keeping the existing water heater, but having the option to switch it to an indirect later.  Since they would be venting the new boiler through the side of the house couldn't they do the same for the existing water heater, or is that not possible?


  • Tim McElwain
    Tim McElwain Member Posts: 4,560
    With the masonary chimney

    the water heater by itself may not be able to develop enough Delta T (temperature difference) which along with the height of the chimney develops draft measured in water column as perhaps -.01 or -.02 up to -.03 for proper drafting. This in turn would result in poor combustion and eventually high levels of carbon monoxide being created.

    Most conventional water heaters do not allow for side wall venting so that is not an option.

    Another option would be to run a type B double wall vent up through the existing chimney (it then becomes a chase) sizing that vent to handle the existing water heater. If your existing chimney is a straight run up to the roof this is a fairly simple solution.
  • Mike Kusiak_2
    Mike Kusiak_2 Member Posts: 604

    Tim, if the masonry chimney cannot develop enough draft for the water heater without the boiler, what happens during the summer when the boiler is shut down? Wouldn't it be the same situation as if the boiler was removed and only the water heater remained connected to the chimney flue?
  • Tim McElwain
    Tim McElwain Member Posts: 4,560
    Mike it is usually the case with

    gas boiler or furnace with a water heater that the pilots on both appliances run 24/7. The combination of two pilots keeps some delta T in the chimney so the systems can function off that set up. I have seen flue temps in the summer time at 100 to 150 degrees with just the pilots running.
  • meplumber
    meplumber Member Posts: 678
    Flue gas condensation

    Flue gas condensation is also a concern in a masonry chimney with only a DHW heater on it.

    An 8" diameter masonry flue with a 4" atmospheric water heater venting into it not only may not produce enough draft but the cooling of the flue gases could deteriorate the masonry pretty quickly depending on the climate in your location and the amount of the masonry exposed to the cold outdoors.

    Also in the summer, the physics of draft change with the air temperatures.
  • Tim McElwain
    Tim McElwain Member Posts: 4,560
    B vent is cheaper than

    a liner and has 20% more capacity than a liner. Also in many locations you have to have a licensed chimney sweep install the liner. B vent however can usually be installed by the tradesman.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,244
    Why not save the money now and later?

    Install an indirect now to save on fuel and to not spend money on a chimney liner or B vent you will throw away later. Also this will give you a clearance to remove the chimney for more room in the house. Are the heat emitting units large enough to gain from a condensing boiler? I am saying are they capable of warming the home with water temps in the lower range during the shoulder months? Is the chimney in poor condition? Is your system hot water with radiators or baseboard?
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • Tim McElwain
    Tim McElwain Member Posts: 4,560
    mbarrett03 you have a lot of

    options offered here and by the way the water heater may be okay with being in the chimney by itself, Your contractor was being very honest with you with his approach. Go with the new install and leave the water heater in the chimney and see if it works. If so then when it goes install the indirect.
  • Tim McElwain
    Tim McElwain Member Posts: 4,560
    Now the rest of the

    process as Charlie mentioned is adapting the Mod/Con boiler to your system.

    Condensing boilers do not give maximum performance unless the return water temperature is below 140 degrees. That being said if you have fin tube baseboard which requires 180 degree water then with a delta T of 20 degrees your return temp is only 160 degrees. Have your contractor do a heat loss on the house and measure your emitters (radiator, baseboard, convectors) what ever you have and see if you can operate at a lower temp to the emitters and still get adequate heat transfer. That along with outdoor reset should make the system operate as it should.
  • mbarrett03
    mbarrett03 Member Posts: 10
    Wow, thanks to everyone for all the replies,

    especially you Tim for providing so much insight.

    Charlie: you have a great point there. To touch on your questions, the chimney is in good shape. I just had it inspected a few weeks ago and found that the top could use some re-pointing, but it is otherwise OK.  The hotwater system is with baseboard. Not sure if this is relevant but the house is about 2300 sq ft on 2 zones (1for first floor, 2nd for second floor).

    Another company is coming over tomorrow to give me a second estimate, just so I can compare against the first one I received.  I'll ask him about doing a heat loss, and also what he thinks about the water heating drafting up the chimney with and without the B -vent. 

    Thanks again for all the input - you guys have been a great help.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Heat loss on fin-tube baseboard.

    I did a heat loss on my upstairs rooms (2). One was about 3200 BTU/hr and the other was about 3400 BTU/hr. But each room had 3 feet of baseboard, and they were usually cold. Since I was about to put a mod-con in there, I wanted condensing. That would have been fine for downstairs (radiant on-grade slab) but no condensing upstairs. I figured out that I would have to increase the baseboard up there. The width of the rooms up there (under the windows) was 14 feet, so I figured out what temperature I would need, about 130F (supply) on design day if I had that much put in. So I had the undersized baseboard replaced by two 14' pieces (actually four 7' pieces joined in pairs). Works fine as far as I can tell (it got down to 14F outside last winter for too short and interval to see if that is enough, but it is pretty close in any case.
  • bob eck
    bob eck Member Posts: 930
    condensing gas boiler

    If you use a Triangle Tube Prestige boiler with a indirect water heater you can use your old chimney if it is strait up as a chase to run the pvc pipe up it to vent the boiler and you can bring in the fresh air from the side of the home. If running pvc pipe up the chimney to vent the boiler you can NOT vent anything else into that chimney. If you get the boiler installed by 12-31-10 there is a federal tax credit of 30% up to $1500.00 that you can take on your 2010 federal taxes.
  • mbarrett03
    mbarrett03 Member Posts: 10

    Hi all. I decided to go with the new boiler and indirect water heater. Just had it installed last week. I felt bad about getting rid of the 2 year old DWH but in its place I got a stainless steel superstor w/lifetime warranty. And the new boilder is direct vented so I don't have to worry about the chmney lining any more.

    Thanks to everyone for their advice and suggestions.
  • bob eck
    bob eck Member Posts: 930
    new boiler

    what brand boiler did you buy? any pictuers?
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