! Important: some electric boilers come with a flow switch (extra safety measure to protect the heating element from over-heating if there's no water flow), while others do not. A
flow switch is optional for most of the country, but is required by code in some places, such as NYC and others. It may be purchased separately from the boiler if needed.
Electric Boiler Sizing
As with any boiler, sizing should be performed based on the BTU/sqft requirement in your specific climate. A simple formula is:
ΔT x Space (ft
3) x 0.133 = BTU's.
Where ΔT (Delta T) is the temperature difference between coldest and desired, and Space is the volume of the heated area in cubic ft.
It is important to not oversize the electric boiler, as a larger unit would require larger diameter wire and larger breakers, resulting in higher installation costs. At the same time, when in doubt or selecting between (2) models based on calculations - select a larger one to avoid under-heated space.
BTU/sqft varies considerably by climate and other factors such as age of the building, insulation, number of windows, etc. An experienced installer should know these numbers and easily make the calculations such as the ones below:
Example 1:
If a BTU requirement is known to be 50 BTU's/sqft, then a 24kW (82,000 BTU) electric boiler would cover approx. 1,640 sqft; a 20kW (68,200 BTU) model - 1364 sqft; 16kW model - 1092 sqft; 12kW - 820 sqft and so on.
For 60 BTU's/sqft, these numbers would be 24kW - 1366 sqft; 20kW - 1136 sqft; 16kW - 910 sqft and so on - on average, +17% higher than 50 BTUs'/sqft.
Example 2:
If BTU/sqft is not known, but the coldest temperature and area (or volume) are known: a 1,000 sqft basement with 50F temperature needs to be heated to 80F. Standard ceiling height is 8ft. Delta T is 30F (common), total volume is 1,000 x 8 = 8,000 cu. ft. The final formula is 30 x 8,000 x 0.133 = 31,920 BTU's. A closest match would be a 10kW boiler model.
Keep in mind that these calculations presume that radiant floor heating is used and the space (including floor) is well insulated. If installing a boiler in conjunction with an indirect hot water tank, it should match the maximum/peak DHW (Domestic Hot Water) load.
Electric vs Gas Boilers
Pro's: electric boilers are very compact (easily installed in confined space with minimal clearances), require no chimney or vent pipes (meaning no drilling, no cleaning and no carbon monoxide) and since they don't need gas - are much simpler in construction and easier to repair. With proper installation, the only component which may go bad with time is the heating element, which is easily replaceable in most instances. Plus, they produce zero emissions and may qualify for a federal or state rebate program.
Cons: the main downside of all electric boilers is considered to be the wiring size and very large circuit breakers, which may require modifications to or an overhaul of the breaker box and/or electric system to match the boiler's needs. However, since an average home in the USA has 100 - 200 electrical service amps, it should have no issues adding an average size electric boiler unless the system is working at full capacity (which is most often not the case).
Which parts are needed for an electric boiler installation?
Electric: All electric boilers we sell (except Stiebel Eltron) come with integrated breakers and will require appropriate gauge wire and breakers (see specs & manual for details) for power supply.
Plumbing/heating: all boilers (except Stiebel Eltron) come with a standard 30 psi 3/4" pressure relief valve and have connections for LWCO (optional), circulator pump and thermostat.
If a boiler is used in a single-zone configuration, a common 2 or 3-wire heat only thermostat and a 120V 1/6 Hp (or smaller) circulator can be used.
For multi-zone configurations (with individual room temperature control), when zoning with multiple thermostats and choice of either zone valves or circulator pumps, refer to the wiring diagrams of the zone valve controls or switching relays respectively. Most multi-zone hydronic controls on the market are universal and will work with other brand valves or pumps. For example, Taco ZVC or Argo UZ/AZ would work with Honeywell/Resideo or Taco zone valves; Tekmar or Argo ARM switching relay would work Grundfos or Taco circulators, etc.
The rest of the piping is the same as with common gas boilers - expansion tank, air eliminator, boiler feed valve (fresh water supply), etc.
For radiant floor heating applications, an Everhot SSM or BSM series manifold with or without actuators (zone valves) can be used.
Since all electric boilers utilize immersion style heating elements, we strongly recommend either a water treatment device or a manufacturer approved scale inhibitor additive to prevent scale formation. The best practice is to test well/municipal water and determine is the above is needed.
