Choosing an Electric Water Heater
richard_r
| Posted in Mechanicals on
I’m committed to going electric (from natural gas) in my remodel. 3 bedrooms but only one person currently. Heat pump heat, induction cooking etc. Planning for solar panels (conduits to roof), but not in Phase 1.
Utility room is in middle of house next to bedroom, so I have ruled out Rheem for noise. Sanden/eco2 is very desirable, just seriously expensive. It also bugs me that I would have two heat pumps outside. Is there a quiet electric water heater worth considering, that would be a defensible choice in Washington state (relatively cheap electricity) given that solar panels are in my future plans?
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Heat pump water heaters, while efficient, come with some downsides as you've identified. For one person, consider a simple electric resistance tank which are both cheap and quiet. If possible, you could fit a drain water heat recovery unit as well, which would bring shower energy usage down by about half. Electric resistance tanks are of course less efficient than heat pumps, but with low usage and low electricity costs you might find it advantageous to keep it simple.
A compelling heat pump option might be the new nyle E8, which is a split system for indoors, which might allow you to place the compressor in a more convenient location. It would pair with an electric resistance tank well, so you can install the tank first and add the nyle later.
Skip a tankless electric heater, they requirement massive amperage and gain nothing efficiency wise.
My stiebel eltron instant electric water heater makes noise in the basement and it’s not in a separate utility room. I don’t find it too be so loud that it would keep anybody awake. Can you soundproof the utility room or at least box in the water heater to reduce noise? Whos running hot water at a time where it would be unbearable noise?
I suppose you're right that noise in an on-demand unit could be less of a concern. I do sometimes host musical events and if someone visits the bathroom and washes their hands....That has been an issue when my Takagi gas-powered unit needs a service :)
On demand units don't play nice with the utilities due to their very high, and relatively infrequent, load profile. You also may need to upgrade your electric service to run one. They do run quiet though.
Heat pump water heaters (HPWHs) are hard to beat in terms of efficiency, especially if you're in an area with a relatively light heating demand for the rest of your home since HPWHs work by scavenging heat from their surroundings.
Your last option is plain ol' electric resistance heat in a tank. These are usually around 5kw or so, so unlikely to require an upgrade to your electric service to support. They are otherwise pretty much the same as gas fired tank-type water heaters, with standby losses (which are pretty low), and recovery time as all tank-type water heaters have. This may be your best option though. In many/most areas, I'd advise that they don't really help to reduce emissions, since the electricity will primarily be sourced from coal and natural gas, but in the Pacific Northwest, a suffiently large amount of the total electric power produced is sourced from hydroelectric plants that you probably come out ahead overall. Note that you will come out even farther ahead with an HPWH if you can tolerate the noise. Possibly consider some minimal soundproofing of your mechanical room if possible as a way to mitigate the sound issue.
Bill
Are solar water pre-heaters being used with any success? It's a lot more efficient to turn the sun's energy into heat instead of converting it into electricity and then into heat. Of course, there is a big difference between Seattle and Spokane.
>"Utility room is in middle of house next to bedroom, so I have ruled out Rheem for noise."
Really?
Are you perhaps trying out for the role of "Princess" in "The Princess & the Pea"?? :-)
The noise specs on current versions of Rheem are pretty low. Rate at 49- 51dbA they are quieter than many refrigerators, even quieter than some mini-split heat pumps. With the attenuation of any partition walls & doors between the water heater and bedroom that water heater noise may not even be perceptible above background to a keen-eared dog.
If the mechanical room isn't big enough to fully support a heat pump water heater's thermal intake (~700 cubic feet- say a 9' x 9' x 9' cube) you may have to duct it to an adjacent room (or above/below), which would project some, but not all of that sound to which ever room it's connected to.''
Bottom line, you'd be able to hear it in the mechanical room itself, but you'd have to listen very intently on a windless day with no other mechanical systems running to hear it from a doored-off bedroom.
It seems like the latest Rheem version is very loud despite the specs.
Dana,
"Are you perhaps trying out for the role of "Princess" in "The Princess & the Pea"
This discussion seems to show it's not a concern to so easily dismiss: https://www.greenbuildingadvisor.com/question/rheem-hybrid-water-heater-noise
I wonder if the objectionable noise is conducted noise and not radiated noise. I’m sure the measurements made by Raheem are for the unit running in isolation, not connected to anything. A unit that is installed, especially if it’s rigidly piped in (copper lines) might conduct noise through the piping and resonant part of the floor above, making it seem much louder. If that’s the case, flexible connections to the HPWH would help, and possibly consider wrapping those flexible lines with butyl noise damping “tape” (it’s really a roll of a thin strip), which can help damp vibrations. I’ve used the butyl tape on drain lines before to quiet them down. I’d be careful if using it on the hot water line though — I haven’t tried that before and I’m not sure if the heat would be enough to be a problem for the butyl rubber material of the tape.
If you have the HPWH near a masonry wall, it can help a lot to rigidly clamp the pipes along the masonry for 5-10 feet too. I do this by wrapping some 1/8” EPDM around the pipe at each strap location, then using a two hole steel strap to attach the pipe to the masonry with a 3/4” thick wood block between the pipe and the masonry. Pipe insulation or butyl tape on the line between straps also helps. You need at least two attachment points per pipe, three is even better. The masonry will help to damp any vibrations in the pipe before they can couple into the wood structure where you might get resonances.
Bill
Based on the discussion linked, it's not just conducted noise, they are just louder than they are supposed to be, and much louder than the previous model. Rheem has tried, with minimal success so far, to redress the issue.
Fair enough.
If this is a serious concern, installing it atop a pad of 2-layers of OSB attached to each other with Green Glue (tm), or even more elaborate vibe isolation solutions will reduce mechanically conducted sound from propagating in the structural materials of the house. Installing air-barriers in both the ceiling & floor joist bays where they cross the partition wall boundaries, as well as air sealing the walls, floors, & ceilings themselves reduces noise propagation in the contained air pathways along framing bays.
Then (where possible) insulating the walls & ceiling & floors of the mechanical room with low-density loose fill insulation or low density batts can make further significant reductions.
BTW: Measuring noise levels with a cell phone app (as some did in the referenced thread link) is a total joke. Phones are not in any way designed as measuring instrumentation- their microphones are not fully isotropic, and depending on how it is used the error can easily be 10s of dbA off what a NIST calibrated sound level meter would read. Treat any phone-app measurement at best as a conversation starter for entertainment purposes, not an actual measurement.
That said, you don't need a calibrated measurement number to tell whether a sound bugs you (or not).
I really don't think two layers of OSB and green glue is going to accomplish much as a floor pad assembly. This 'isolate vibration from the structure' comes up fairly often in the commerical world in multistory buildings where mechanically rooms are installed on high level floors (30th, 50th, whatever) and noise carries through the steel structure farther than you'd thing. The usual way to do it is to place the offending device on a special pad that is a precast concrete slab-chunk in a steel frame on spring-type vibration isolators. There are then flex sections in any piping between the offending device and the rest of the structure. This setup works well, but is probably overkill in a house -- especially if the offending device is on a basement slab.
I think you'd be better off with a simpler arrangement of a large precast paver and cork pad vibration isolators in the corners. The precast paver provides mass to damp vibrations, and the four cork pads help to isolate that paver from the structure. The relatively small total area "connected" between the paver and the structure by the cork pads also helps. A large OSB sandwich with green glue isn't going to be as effective here. Remember flexible couplings for ALL piping too to reduced transmitted noise!
High density batts will help more than low density with sound too, especially if left exposed. Rigid mineral wool is particularly good here since it's easy to install.
I absolutely 100% agree with you about cellphone dB meter apps. There is no calibration at all, they are directional-ish, and they don't respond to the entire frequency range evenly. I have actually compared some to professional level sound equipment, and the response is barely adequate for relative measurements (comparing thing A to thing B using the exact same phone and app in the exact same place), and even then you have to be very careful to orient the phone exactly the same way for each test. The old Radio Shack SPL meters were *far* better. If you're looking for some current semi-pro gear that can make reliable measurements and doesn't break the bank, try this:
https://www.amazon.com/miniDSP-UMIK-1-Measurement-Calibrated-Microphone/dp/B00N4Q25R8/ref=sr_1_2?crid=I1CQ4K2HLXRA&keywords=umik&qid=1655257082&sprefix=umi%2Caps%2C355&sr=8-2
The UMIK-1 has a good reputation for basic sound level measurements.
Bill
The Green Glue falls into the "cheap, probably better than nothing" category. Most of the noise emission is probably at the blower, not the compressor, so there is not likely to be a lot (though some) being transferred mechanically to the floor.
High density batts (covered or not) don't work as well as mid-density batts- the density creates a stiffer mechanical coupling from between the drywall on each side. Most purpose-made sound abatement batts are mid-density, and nominally 3" thick to limit that mechanical coupling through the batt itself.
Air sealing the partition walls/floors/ceilings is probably the first, best approach to limiting sound transfer.
If there are heating/cooling duct penetrations that would be another path to consider. Using insulated flex to connect the plenum to the hard piped runs will help.
Seriously, I've yet to see a recent Rheem installation where the homeowners complained about the noise, though you can always find complaints (about nearly anything) on the web. Admittedly it's a small sample, and usually on s basement slab rather than on a framed floor, but at least some were directly below a bedroom. If it becomes in issue, in most stick-built houses it's not that difficult to make significant reductions in noise transfer into or out of a doored-off room.
Richard,
I'm not convinced that for a small family, an efficient tank resistance heater isn't a better idea.
https://www.homedepot.ca/product/rheem-marathon-50-gallon-189l-lifetime-electric-water-heater-4-5kw-240v-/1001070393
That's what I'm wondering. I see Rheem has a "booster" so maybe 50 gallons is enough, and I can rationalize the inefficiency relative to HPWH with a) planning for solar b) PNW hydro.
Based on everything I've read here about Rheem, I'd never buy one.
Beyond the noise concerns, this article outlines some considerations and products to think about: Choosing and Energy-Efficient Water Heater. Excerpt: “Electric tankless heaters are another option, and they report very high UEFs, up to 0.98. But this thermal efficiency comes with some inconveniences—mainly a huge power draw. Rheem’s RTEX-24, for example, draws 100 amps at 240 volts and requires three 40-amp breakers.”
I made the switch a little over a year ago from a standard electric water heater to a heat pump unit and am glad I did. Electric isn’t crazy where I live but it is still providing a savings of about $300 a year. I have a Richmond unit, which is made by Rheem, and haven’t had any noise issues.
When my electric water heater tank broke 5 years back I switched to instant electric tankless. Yes it draws power like crazy when it’s on but I have enough power and my kids always have a warm bath. My 50 gallon always ran out of hot water, probably just an issue now because my kids take baths. Family of 4 showering would probably not have this issue. I live in downstate NY where electricity is expensive. My bill isn’t much higher, I think because you only run electric when the water runs with a tank it heats all day. Again idk about rheem but my Steibel eltron is quiet if anything the sound of water running is much louder. I don’t get the noise thing, does rheem shake when it turns on? I could sleep with my ear next to the water heater without a problem.
Anybody know if electric tankless is cheaper to operate than a heat-pump tank heater?
I understand that there are other reasons to avoid electric tankless, but purely looking at operating cost, would electric tankless or heat-pump water heater use less electricity for say, an average family of 2-4?
No. A heat pump would be 3-4x as efficient as tankless electric. Tankless electric ties an electric resistance tank in efficiency.
There is a belief that tankless anything is somehow more efficient. It is not the case..
A heat-pump water heater should use less electricity than an electric tankless water heater.
Thanks for the input. I remain concerned about noise from HPWH, but a new possibility has arisen - place one in the external storage room (which will be semi-conditioned). i.e. pink star vs blue star. We will be opening the living room ceiling for insulation so there will be an opportunity to do the plumbing. The storeroom is 42" wide but over 8 ft tall. But note piano. Given that I'm in the Pacific Northwest and planning to add photovoltaics eventually, it's tempting to just go with an electric tank at the blue star location.
There are a lot of variables but my guess is that for less money than buying the heat pump water heater and the panels to run it you could buy the standard electric WH and the panels to run it for less money and have a quieter more reliable system.
Walta