Hot Water Heaters Tankless vs Tank Units

Hot Water Heaters Tankless vs Tank Units

What are the applications and benefit of tankless vs tank hot water heating unit. Is it worth switching or just wait till the current unit needs a change. Is there more maintenance on one unit vs another.

If the energy bill seems higher than it used to be and no other major units have been added to your energy system, it may be time to check the hot water heater.

Hydro One has touted the water heater as one of the biggest energy consumption units in the majority of households.

With either system, be sure to get the right size for the property, as well as occupants and useage.

Running costs:

Cost per annual use – fairly par – some manufacturers suggest upto 40% less energy usage on a tankless unit (likely on a gas unit over electrical), but energy star in side by side comparison has touted an $8 difference per month – unless units are overworking due to scale buildup.

Limitless hot water – is the main feature, that there is continuous flow of hot water in an on-demand unit, tanked units have a gallon limit and must reload and reheat.

Instant hot water is a bit of a myth with tankless units, as the water, although on demand, still needs to get from the unit through the pipes to the faucet.

Instant hot water would need a circulation pump close to each faucet that instant hot water is required.

Wireless mobile apps now available on some units, real time data can be accessed instantly.

Space Savings:

Tankless units have a small footprint and are wall mountable. Tank units take up significant both vertical space and floor space. Tanked units come in various heights as well.


Lifespan tankless hot water heaters are generally longer at 25 yrs as opposed to 10 for a tank unit.

However failing to maintain an on-demand tankless hot water heater significantly impacts the longevity of the unit, as well as potentially skyrocket the energy bill.


Tankless units can often integrate with boiler systems, radiant heating, hydronic, geothermal and off grid systems, at a residential, commercial, institutional level. There are excellent hybrid units on the market that handle a myriad of applications, including condensing boilers and direct vent wall furnaces etc.

Have Both – a Hybrid Tank/Tankless Unit:

Hybrid non-condensing series with an 80 gallon storage units are available. Recirculation paterns can be calibrated to coincide with the useage habits. (thus not circulating at non-peak times and creating inefficiencies).

Also satellite tankless mini-units can be added close to faucets to supplement a tanked or tankless system. This is also an option without changing the whole system to get hot water closer to a far away faucet.


It’s rare, but tank units have been known to explode. Think oversized pressure cooker (or rocket technology). Scale embeds into pits that are eroding inside the tank, the unit gets flushed and the scale “corks” stopping the chips in the tank are no longer supporting it. Thus chassis instability. Which is why some insurance companies will not insure a tank over 10 years old (possibly less).

Also, leakage is a major issue with tanked units moreso than with on demand tankless units.

Maintenance Tankless Hot Water Heater vs Tank:

  • Both need to be flushed 1-2x’s per year – unless extremely hard water then upto as much as once per month – if there is more than a cup of settlement then the flushing is too infrequent
  • Flushing not as necessary when a water softener is used.

Tankless Units Maintenance

  • Heat exchanger / elements to be descaled as well 1-2x’s per year
  • A unit with heater set on high attracts more buildup


Flushing a Tankless Hot Water Heater

Rinnai is a leading brand for tankless units for residential and commercial units.

Tank Unit Maintenance:

  • Sediment builds up on heating elements and causes the system to work harder
  • Sediment can block or clog the pressure and the flush valve and become a potential hazard
  • The heater can corrode more quickly or just burn out all together
  • Sediment at the bottom of the tank uses more energy because now the tank is not just heating the water, it must also heat the sediment to keep the temperature at a constant heat level. Can cause overheating and weaken the steel and glass lining.
  • Also many lower elements can get buried in the sediment if it hasn’t been flush in awhile.
  • Only 5 gallons of water usually needs to be flushed not the whole tank.

Tank Water heaters older than 10 years old should be considered for replacement, also check with your insurance company, as often they will not cover damage to the property if a unit is over a certain age and if the heater is the cause (hot water heaters, might not just leak and cause issues, but rarely can explode – similar to rocket technology – in both electric, gas and oil versions

Really old gas units – may not be advisable to flush it before if it hasn’t known to done in recent years. Over time the steel tank and lining could be compromised by sediment sealing small holes in the steel… thus flushing the tank could dislodge the “sediment plugs” (think plugs in a dam) and now the tank is perforated on the inside. Suggestion is to call for a consult on that scenario.

Water heater failure signs:

  • Rusty brown hot water
  • Strange noises
  • Water around the water heater

Maintenance needed:

  • Water too hot then runs out quickly
  • Water not hot enough

Could be burnt out element or burnt out rheostat (different than the thermostat, each element rod has its own rheostat which controls the current to that particular heating unit)


Flush hot water tank

Change anode rod

Change an Electric Water Heater Heating Element

Anode rod

  • hard water aluminum is the choice most technicians recommend
  • soft water is usually a magnesium anode rod
  • for a tank that is in tandem with a water softener – an electrical anode is usually the choice used.

Anode rods are to be changed every 5-6 years – so twice in the lifetime of a tank unit, more if the water is really hard.

If there is too much sulfur (hydrogen sulfide) in the water, often a zinc anode rod is used – made from a combination of zinc and aluminum which helps to reduce the rotten egg smell sulfur offputs.

Pipe joint compound is typically a better choice for your anode rod than Teflon tape, as the tape will likely reduce the effectiveness by electrically insulating the rod from the water heater chassis.

If the smell is from contaminates leaking into the water supply such as sewage or other refuge, this is another matter all together, and could cause health issues.

Most anode rods are the same diameter of ¾ inch – but different lengths depending on the height of the tank.

Rheem has a reputation for manufacturing durable and reliable water heaters, in an affordable price range, which makes it a good choice for most homes.

If there is an immense amount of sediment in the bottom of the tank, it is very likely that the heating elements are coated in calcium and other minerals as well. It would be a good time to check them, as energy useage will still be high even if the tank is flushed yet the heaters are still coated.


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