Summer Boiler use for DHW with Central A/C

BoilerLife Posted By BoilerLife, May 2, 2019 at 11:43 AM

  1. BoilerLife

    BoilerLife
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    Jan 25, 2019
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    Hey Folks,

    First Summer here with the new boiler (HeatMaster G200). Setup inside is a forced air electric furnace (backup) with central A/C and duct work throughout house, water heater is electric. We might burn this summer for our DHW, we also might not, I haven't decided...few questions on the 2 scenarios below. I attached a pic of setup at the furnace too...A/C coil is at top where black/copper piping enters furnace, the hydronic water-air heat exchanger is at the bottom there where red pex is.

    IMG_20190501_132755.jpg

    Scenario 1 - we completely shut down the boiler and not burn wood this summer. Use electric water heater for DHW, and our central A/C for cooling. Is there a risk of the water-air heat exchanger that sits in the furnace freezing up and bursting from the A/C use? (I was told originally to just leave the water in the boiler/loop in summer, so don't drain it, but shut all boiler power off, circ. pumps, etc - is this correct? - that means water will be sitting still in the water-air heat exchanger in furnace - will this freeze/burst from A/C?)

    Scenario 2 - we do burn wood this summer in boiler for our DHW (electric water heater off). In this scenario, wouldn't the A/C have to work harder because there will be hot water from boiler going through water-air heat exchanger in furnace, so the fan would be blowing that hot air over A/C coil and mixing it with cold air from A/C, meaning the air coming out of vents isn't as cold as A/C working with boiler loop shut down like in scenario 1? If I am thinking of this correctly, how do you get around this - would you need by-pass valves/piping at the water-air heat exchanger in furnace so the hot water in boiler loop doesn't go through that exchanger, and it just skips it and continues along the loop back to the boiler - this way no heat from boiler water enters the furnace during A/C use and A/C would just function as normal and we can still burn wood for the DHW only?

    Thanks.
     
  2. maple1

    maple1
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    Sep 15, 2011
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    My random input.

    On 2, yes you should be plumbed so you can bypass the HX in summer.

    On 1 - which way is the air moving? I would usually assume up. In which case the air movement would be away from your heating coil. In any event, I wouldn't expect it would freeze the coil - but I have no direct experience.

    I could heat our DHW with wood all summer, with a weekly burn, if I wanted. But I don't bother. Electric only runs about $25/mo to do it.
     
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  3. BoilerLife

    BoilerLife
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    Jan 25, 2019
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    Thanks for the input Maple.

    For 1. The air is moving up yes, I was more thinking for when the A/C is sitting idle and the auto-fan is off? Just thinking of the temps in that scenario and if A/C coil would be too cold for heating coil (which would have still sitting water in it in this scenario)...they seemed to be spaced apart by about 2ft. in plenum...not sure what to expect...first summer with boiler.

    For 2. I was thinking the same thing about using bypass - another question on this, once the HX is bypassed, should the HX have "still boiler treated water" sitting in it for summer, or should it be bypassed with no water at all sitting in HX for Summer months? Does it matter? My guess would be boiler treated water sitting still?

    I would normally do scenario 1 and not burn in summer and use electric heater for DHW, but we have a bunch of scrap wood we need to burn anyways before it all rots out, more of a wood clean out routine this summer.

    Thanks.
     
  4. E Yoder

    E Yoder
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    Jan 27, 2017
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    If your AC coil freezes up it most likely is low in refrigerant or airflow is way out of whack. I'd just check it the first day or two. Should be fine.
    Once those coils get water in them they are almost impossible to drain anyway. I'd just plumb a bypass just after your hot water heat exchanger and let the lines and coil go cold. You don't want even lukewarm water circulating through it as it can make the AC work harder. The AC puts out ½ to ⅓ the BTU's in cooling as the heating coil does so running with both will heat (like to 90°, we've gotten those calls, Lol).
    I run my GS100 in the summer burning scraps. I light the charcoal at the nozzle with my torch, load with scraps, run it up to temp, then kill the switch for the control. Just a once a day batch burn. Works really well, no smoke or creosote from idling all day.
     
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  5. BoilerLife

    BoilerLife
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    Jan 25, 2019
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    Thanks Yoder - do you happen to have a picture of that by-pass setup you explained above? I will have to explain this all to my plumber. I was initially thinking of just having the bypass right at the water-air heat exchanger at the furnace - in between those 2 red in/out pex lines...figured that would be the easiest...but are you saying if the bypass is located there that the water in the heat coil could still reach luke warm temps because of the heat transfer at the bypass?

    If setup to bypass after water-water heat exchanger, so that bypass pex tube would have to then lead directly to the "return" line leaving the house back to the boiler right?
     
  6. E Yoder

    E Yoder
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    Jan 27, 2017
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    I use a 3 way valve, it has an L port to send flow right or left. But two tees and two ball valves works fine too.
    In this picture the red line goes curves around to the right out of the picture to go through the flat plate, then comes back into the 3 way valve on the blue line. It then can be directed through the coil or bypass on the blue line.
    I think if you stay at least 3 feet above the coil heat won't migrate through the piping into the coil when in bypass mode.
     

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  7. BoilerLife

    BoilerLife
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    Jan 25, 2019
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    Thanks Yoder - I will have to get this setup going.
     
  8. E Yoder

    E Yoder
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    Jan 27, 2017
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    The L port valve is a Webstone, available on supplyhouse.com and elsewhere.
     
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