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Torn between tankless, hybrid, and power vent water heaters

agurkas | Posted in Energy Efficiency and Durability on

We are going to be removing the chimney and steam boiler with indirect water heater attached to it. Heating and cooling of the house is covered by air source heat pumps and living room is heated by 98% efficiency natural gas furnace.

So now I have a choice to make to replace the water heating setup between three choices:
1. Power-vent water heater seems to be the cheapest route, but I was hoping to draw air from outside and don’t think my plumber knows any with that option
2. Siemens tankless high efficiency unit
3. Go with hybrid heat pump water heater

My architect likes #3, since I have 1100 sq ft basement and since it is older kind, it can always use some dehumidification. My concern is I am in Boston area, which is Zone 5, and that heat pump will be eating a lot of heat from my house.

#2 seems to attract as many opinions as plumbers I spoke with.

#1. 83% efficiency units sucking air out of the house, yet the cheapest option.

Thoughts? Advice?

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  1. Expert Member
    Dana Dorsett | | #1

    Almost all condensing hot water heaters are direct-vent/sealed combustion but I'm not aware of a non-condensing tank that is.

    Takagi 's residential condensing tankless units are cheap & rugged, so what if the EF is only 0.95 instead of 0.98 or whatever the Siemens is? Takagi may be a second-tier company in the tankless market, but they have great on-line/on-phone service out of their CA office and their products have a pretty good track record. (I'm comfortable enough with them to have been heating my house & hot water with a Takagi for the past half-dozen years, with very low maintenance and zero problems. At my use levels it's the equivalent of 20-25 years of service as a hot water only heater, though I'm not running more corrosive potable water through it, only heating system water.)

    The amount of heat that a heat pump water heater would be "eating from" the house in a Boston climate is a small fraction of the heat load for most house, a load which is being supported by a 98% efficiency gas-burner. It doesn't get much better than that.

    But wait, it DOES get better than that!

    At Boston summertime outdoor dew points almost all basements need some mechanical dehumidification to keep the mold-spore count down. Running a dehumidifier turns a latent cooling load (humidity) into a sensible cooling load (heat). Rather than heating up the basement in summer with a dehumidifier, a heat pump water heater heats up the hot water with that latent heat conversion. I go through about 500-600 kwh/year dehumidifying my basement in Worcester to under 60% RH in summer. If I was heating the domestic hot water with an EF 3.0 heat pump water heater I suspect the dehumidifier would never turn on.

    Your architect has it right- there's more up side to down side with a heat pump water heater solution.

  2. agurkas | | #2

    Dana, you must be friends with my architect :-) You probably know him too.

    I am going to put in PV and have become very big fan of heat pumps. So looks like GBA and my architect are hell bent on getting natural gas usage in my house to zero.

  3. GBA Editor
    Martin Holladay | | #3

    Another vote for the heat-pump water heater. An all-electric future is on the horizon... might as well get ready for it.

  4. agurkas | | #4

    Oh no. Martin is in this one too :-) So I guess I need to put in a gym in that huge basement room, so there is heat to scavenge for the heat pump

    GE Geospring seems to be one I am coming across as a popular one

  5. user-2890856 | | #5

    Dana , Addressing the Takagi comments . These are not the same as the one you were fortunate to purchase some years ago prior to a merger or aquisition deal . Not so good or rugged anymore sorry to say .
    In this instance I would agree on the recommendation of a HPWH .

  6. Expert Member
    Dana Dorsett | | #6

    Richard- thanks for the heads up! Sorry to hear about Takagi taking a quality-slide. :-(

    Apollo: You'll find a lot of product bashing reviews of the GeoSpring online, but most of those are on first-generation versions which had both design issues and manufacturing quality issues. The second-gen product was built in Kentucky rather than from multiple sources in Asia, but still had some design issues to be ironed out.

    The current third generation product is both considerably higher efficiency and a by all accounts a better design (third time is the charm?) and should be (finally) ready to go the distance. I wouldn't be afraid to install one in my home if I were in your shoes, but keep the documentation in a safe place, and fill out the warranty card. (GeoSpring would top my "best value" list of current HPWH offerings.)

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