Here is a report on energy consumption and usage patterns on some Canadian homeowners who switched from storage to tankless. You can see the range of results. There were usually operating savings but those savings might have trouble overcoming capital cost and maintenance disadvantages.
Great Report! Looks like a lot of Navien's (my personal favorite).
Big percentage savings, not so big money savings. Annual savings $69 a year.
Location! Location! plus, number of residents, plus what else is needed. If you live in an area (Florida, Texas, anywhere else in the sunbelt) solar hot water may be the way to go. We have found that electric tankless in a normal residential setting - 3 plus in the home - is not an economical choice! If you live in a condo with no gas and limited space and only one or two residents electric tankliess may be the only way to go. If you choose electric how many more 220 circuits must be added? Just remember with any tankless option - everytime you turn a tap on for hot water - washing hands, shower, dish washing,etc. you will be charged for the fuel/power needed. We have also seen electric tankless needing more maintenance than gas. Even in forty-five degree weather - if the sun is shining solar can deliver 120 degree plus hot water! For free. There is a federal 30% tax credit and most states have an additional incentive in the form of a solar rebate! Electricity is the least efficient way to make hot water!
1kW of electric is approximately equal to 3427 BTU's of heat. In electric hot water heaters close to 98% of the 1kW is used to heat the water... the other losses are in thermostat - and wiring up to the heater.
Once the water is up to temp (presumably 120F), then the water heater losses are mostly via conduction and radiation through the tank walls. If hot water demand is low, you can have a lot of loss through the walls. The tankless deals with that loss by only heating as needed - but that as you noted introduces a whole new set of problems - the very high peak electrical loads to provide the instant heated water.
Baseboard heat for a room is like a hot water heater - efficient if all you need is spot heat. But most homes also need some additional ventilation. The base board heaters do not provide ventilation. If you are in a location with very low electric rates -- base board heating may always pan out to be the lowest cost option. But when you need air movement for ventilation and electric is the option - then a heat pump with a coefficient of > 1 beats the base board option.
If you are have a very high performance house (air tight, well insulated, etc) in floor water heating systems are sometimes preferred because the room heating is very even - and the ventilation is done with separate HRV/ ERV air ducting. The in floor heat allows the designer to use the mass to help moderate the temperatures and allows the heat to come from air source heat pumps, ground source heat pumps, geothermal, solar thermal, electric boilers, etc.
To me its all all about total system BTU's to what is needed to wash your self to what is used pumping water then the wasted water getting cold to hot down the drain, Then getting 160' water mixed with 70' to get 120' water. OK lets heat water 24/7/365 to 150" then run down a copper pipe that wasted 8 gal of cold water to get hot to work. lets take a 50 gal tank of water heat in up 150' then use it for 10 min each day. Then waste the hot water down the drain just to heat up the bugs and ground. Most hot water systems are some 1% eff or less. If the heater is a cup away from use and just turn on for the use then can get 90% eff.
I just left a building with $40,000 Hot water heating system with main line of of 2" copper going 1200' 99% of time most just want to wash there hands. It takes some 97 gals of water to get the bath hand washing 100' so you can wash your hands with hot water. I asked the office staff when do they get hot water to wash hands and no one in 4 yr got wash in warm water. Homes are smaller but same long long runs and lots of heat to do a little job
Sounds like a small point of use electric would be the most practical for them.
The cost to make hot water is in the fuel costs! Can anyone answer why Hawaii since 2010 requires all new residential, major retrofit residential, and small commercial builds requires solar hot water? Simple - fuel costs and demand on the grid! I don't have the numbers from the midwest or northeat but in the sunbelt if you don't have a pool your hot water system is the second largest user of power in the home! If you can eliminate the need for fuel you can come out a big winner! How many fires or deaths are caused by gas hot water heaters? Then again how many dryer vent fires are there annually? The homeowner or renter still needs to do some maintenance - even if it just a look see. It is recommended that heating /cooling systems are checked at minimum annually! How many homeowners ever check/inspect the hot water system? If you have long runs to get from the tank to a bathroom a simple recirculation pump with a timer solves the majority of those issues. If you can make hot water with no fuel then isn't that the BEST option?
That works in Hawaii. Today my rooftop PV modules are under snow. Last week they were under snow. Sometimes they stay covered for 4 months. If they were my hot water system, that would be a long time between showers ...
Don like I said originally - location/ location/location! The sun is not limited to Hawaii! I know in some places there is snow - poor Buffalo - and lots of overcast. Where there is a good source of free fuel - sun/wind/geothermal/boimass - then maybe we need to change the way we think in our construction practices. That's all.