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Buffer Tank Size vs Boiler Cycle Times

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JustinS
JustinS Member Posts: 258
in THE MAIN WALL
I'm going to be installing a buffer tank and am trying to pick the appropriate size - I've put a spreadsheet together to help me compare boiler on/off times, depending on water temp and # of zones calling...

These numbers are for a 30-gallon tank... the HVAC company did a heat-loss that shows my house would be ~46K BTU/hr with a design temp of 9 degF outside and 72 degF inside... I think that this is high because it's been as low as -10 degF lately and we've not had any trouble keeping the house at 67 degF, using 160F water for

This is both small zones calling (~30k BTU/hr @ 180 degF)...

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  • JustinS
    JustinS Member Posts: 258
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    Looks like some of my post got truncated...

    ---- RE-POST ----
    I'm going to be installing a buffer tank and am trying to pick the appropriate size - I've put a spreadsheet together to help me compare boiler on/off times, depending on water temp and # of zones calling...

    These numbers are for a 30-gallon tank... the HVAC company did a heat-loss that shows my house would be ~46K BTU/hr with a design temp of 9 degF outside and 72 degF inside... I think that this is high because it's been as low as -10 degF lately and we've not had any trouble keeping the house at 67 degF, using 160F water for <= 10 degF outside

    I don't know if I'll get down to 90 degF supply water but assuming that I do in the shoulder season, is a cycle time of ~90min (~5.3min ON and ~86min OFF) acceptable? I think that the ON time itself might short but given that it would take over an hour before the boiler needed to fire again, the total cycle time seems fine, right?

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