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Sturbridge, Massachusetts — electric boiler

user-3368124 | Posted in GBA Pro Help on

Sturbridge, MA. Have abundant PV, similar to Ed Jones’ question. Need electric boiler recommendations. 40 panel ground mount lease. Put in at the height of recent depression. VG deal.

Property has small slab, under 900′ sqft,, 3” foam under and sides. low e glass, 2×6 walls.

Have abundant solar PV, no electric bill, even this winter. I do clean the panels after storms.

Current fuel is wood, we do not need to discuss.

I would rather use up more solar electricity, instead of sell it back to the grid.

Standard HVAC guys, really cannot grasp this. Most go right to propane ..

The slab is a great flywheel and I am addicted. Once warmed the temp differential of circulating water averages only a 2 degrees or less …. slow to take and release …

Need recommendations for electric boilers and whether a buffer tank should be used.

heat loss estimate 20k BTU (2 of the hvac came up with that #) –

My thought is 6kw? to 9kw ? Brands?? Cost Estimate?

If there are other ideas, please advise.

Because of building design I can isolate a HPHW heater and not be stealing from myself.. from a 1000 sqft basement adjacent… leaky and damp, unheated and always at 55 degrees.

I realize we can go straight to Minisplit and get AC but am hesitant, the slab is like have AC in the summer.

Thank You – Howard

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  1. Yamayagi1 | | #1

    For maximum HW electric generation efficiency, I would go for an R744 (CO2 refrigerant) "ECO-CUTE" heat pump water heater. Except that they are very expensive, and as far as I know, they are not on the market yet in the USA.....Ubiquitous in Japan and more and more in the European market, but not here. Oh, well. Sorry.

  2. GBA Editor
    Martin Holladay | | #2

    I don't think that Howard is asking for information on air-to-water heat pumps. But EcoCute heat pumps will soon be available in the U.S., so if you have a personal interest in these units, you way want to read Split-System Heat-Pump Water Heaters.

  3. Dana1 | | #3

    Sanden's EcoCute (the version that will soon be released in the US) has neither the freeze protection for that climate nor the output capacity at Sturbridge's 0F outside design temp to be a great fit here. (It has been fairly deep into negative single-digits F in Sturbridge in the past few weeks.)

    If the heat load is truly 20KBTU/hr a 6kw boiler could handle it without buffering (and the cost of the buffer tank would be many times that of a 6kw electric boiler, which should be $750-1K, not more.) No need to go much higher than that, since the buffering effect of the thermal mass in the slab will keep you from losing much ground even during cold snaps.

  4. user-3368124 | | #4

    Thank you for the feedback, I realize the electric boiler seems a bit outdated, but when you consider investment dollars, to the excess electricity we produce, my common sense brings me back to using the PV to power the slab.

    Air to water heat pumps just do not seem cost effective or really ready yet.

    Last week I brought another hvac.. who first went to propane, then to new Mitsu low temp HP with 2 heads, (the space, due to a wall jog and dog leg) the heads were 9k btu each- pricing was what others had suggested within a $100 dollars, $9k installed. He was the 4th who did not like the EB idea.

    Installed electric boiler may go $2500 ... (my guess) .. I may have a $100 per month electric bill for 6 months of the year instead of selling excess back to the grid. or Spend $9k on minisplit have a $35 month ? electric bill ...( Minisplits do condition the air, that is a plus 20-25 days per year). or I can keep splitting wood ..

    A year or 2 down the road, technology may bring something even better.

    Pretty accurate logic?

    Thx. H

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