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Combination tank

DT437DT437 Member Posts: 5
I have a Bradford White combination tank for domestic hot water and heating (air handler/fan coil). Looking to replace the tank, e.g., another Bradford White, Polaris, A.O. Smith Vertex. What’s best? Or should I consider tankless combi? It’s a two story townhouse in Southern Ontario (zone 6A?), approx 1100 sq ft. The tank is in a bedroom closet on the second floor.


  • kcoppkcopp Member Posts: 3,523
    How many bathrooms?
    I HOPE that the current unit in a Bedroom closet is direct vented...meaning it has a separate intake and exhaust piped into and out of the boiler...

    A combi unit MAY work.
    Drawback may be gas pipe sizing.
    Current set up prob is 40k btu
    A good combi is prob 125k btu.
    Pipe may not be big enough and would have to be upsized.
  • DT437DT437 Member Posts: 5
    There’s a motor on top. Just one pipe. Not sure if that makes it a power vent or a power direct vent? The pipe goes outside horizontally. I’ve been told a replacement tank would need the two pipes or concentric piping.
    Two bathrooms.
  • GroundUpGroundUp Member Posts: 1,014
    What are the heat loads? The Vertex is condensing which requires a drain for condensate, and also is domestic water only with no space heating exchanger on top of being 2.5X the burner size which would likely require a larger gas line. A combi unit will likely also require a drain and larger gas line. The Polaris will have similar demands to the Vertex, less the heat exchanger. For a direct swap, the BW Combi-Cor or Laars Combi-Heat are the only 2 that are going to fit the bill as far as I know- at a cost of some efficiency. If it were mine, I'd stick with the combi tank
  • DT437DT437 Member Posts: 5
    There’s a drain line next to the tank. The pan under the tank connects to the drain, as does another pipe coming from somewhere in the system (maybe the air handler/fan coil?). I was told the gas line is good for an IBC combi boiler or a Polaris. I’m open to whatever will work best and is safest due to the bedroom closet location.
  • kcoppkcopp Member Posts: 3,523
    I have installed a few dozen of the IBC DC 20/125 combi boilers.
    They are quiet and reliable.
    They are direct vent which is a must have in your situation IMO...
  • DT437DT437 Member Posts: 5
    Why would a direct vent be better than a power vent in my case? (I have lots to learn) Would the power vent BW combi tank with the two piping/concentric be as good and safe as the IBC combi boiler?
  • kcoppkcopp Member Posts: 3,523
    Since you have a fuel burning appliance in a closed area you need to bring in combustion air for the burner burn well. If there is not enough air you will have a VERY high probability of Carbon monoxide being produced. That will kill you in short order.
    Either unit will work. The combi will be a bit more efficient and will need more service than the tank. W/ proper service it will probably last longer than the tank.
    Generally speaking I do not like the concentric venting. Too many issues w/ sucking in flue gasses. I prefer two separate pipes.
  • mattmia2mattmia2 Member Posts: 1,619
    the htp pioneer is also an option although i don't know how it compares in cost
  • DT437DT437 Member Posts: 5
    How will the IBC perform in a cold weather climate? Cold winters/humid summers. Is there enough flow to take a shower or run the dishwasher at the same time it’s providing heat during the winter? What about cycling issues?
  • kcoppkcopp Member Posts: 3,523
    Im in New Hampshire... it was 6F (-14C) when I got up this morning… they work fine if the system is designed right. Doing concurrent multiple showers may/may not be an issue. All depends on flow rate. These are good questions for your installer since they will know exactly what you have.
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