Electric Boiler for In-Floor Radiant Heat — Electricity Consumption

evelyntoronto

We’re looking to install a hydronic in-floor heating system in our basement (we’re in Toronto, Canada — Zone 6 by Canadian standards, Zone 5 by USDA). Initially, we were exploring a combi boiler with a buffer tank to mitigate cycling issues, as our space is small (~500sf). With limited space for a buffer tank, however, our HVAC specialist suggested we consider a small electric boiler. It checks many boxes, but my primary concern is on operating cost, as electricity is expensive where I’m located. Given the space and climate, I’m wondering if there’s even a rough way to estimate the kWh we’d need to run the system for a given period of time? Ballpark is fine! As background, here are the details of the unit and system proposed:

Unit:  Thermo 2000 Mini Ultra 3 Electric Boiler

System:  HVAC specialist has proposed laying down Amvic R-10 insulation panels across the basement floor, with 1/2” PEX piping inside the insulation. Note: the boiler will heat only the ~500sf in-floor system. The remainder of our house is heated with forced air (gas furnace).

Any perspectives appreciated!

Hot_water_fan

Underground heat losses should be very low and your space is small. If it’s 500 sqft, your heat loss might be 2500 Btu at 0F (roughly). At 6000 Heating degree days (base 65F), that’s 6000 HDD x 24 hours a day x 2500 /(65-0). Divide by 3412 Btu/kWh, and you get ~1600 kWh. That’s about $180 USD/year where I live, so saving money on the install is probably much more financially sensible than chasing operating costs.

Another option would be to use an electric space heater for a few days to see if you even want the radiant floor.

fentonc

if the heat loss is only 2500 BTU/hr, that would only be an average of 5 BTU/hr-ft^2 - I’m not sure the floors would actually feel warm, if that was your motivation.

Jamie Hall

May I ask why you go to the bother of hydronic in-floor heating and then power it with an electric boiler — instead of going with straight resistance in-floor electric radiant heat? The cost of the electricity to keep the place as warm as it can will be pretty much the same either way — the electric in-floor will be slightly cheaper (no pump) — and the installation cost will be much less for the electric in-floor.

Now if you were thinking of an air to water heat pump and then hydronic in-floor, that's a completely different beast. Your operating cost will be less (at a guess, about half(, but the installation and capital cost will be MUCH higher.

EdTheHeaterMan

A BTU is a BTU is a BTU

• 3412 BTU in a Kilowatt of electricity
• #2 fuel oil is about 138,000 BTU per gallon of oil
• Propane is about 92,000 per gallon
• Butane is about 102,000 per gallon
• Natural gas is 1,075 about per cubic foot or 100,000 BTU per therm

You can find an oil boiler with efficiency of 80% to 85% So you need to reduce your 138,000 to maybe 115,000 BTU per gallon depending on the appliance efficiency

You can find Gas boiler from about 80% to over 95% efficiency. Based on the appliance you will need to reduce the 1075 BTU per cu.ft. or 100,000 per therm to a lower number.

Electricity is basically 99.9% efficient, so 3412 BTU per kW is about 3412, per KW paid for.

Once you have your costs per energy, you can do the math and determine the cost per BTU. There are online conversion calculators that make this task easy

https://www.amsenergy.com/fuel-cost-calculator/

This one does no account for the efficiency of the appliance

hot_rod

A basement under heated space? if it is a basement completely inground, no walkouts I would guess the load would be 10- 15 btu/ sq. ft. So maybe 5000- 7500btu/hr on design day. Possibly much less depending on insulation.

With a low load like that you may not experience warm floors? But you would still heat the space with radiant floors.

In a 68°F room the floor would be about 74- 76° (24°C) to provide 15 btu/ft. Skin temperature may run 82- 84°F 29°C

A 2500W element in a 12 gallon electric water heater would cover it.

Electric mat or cable would be an option, skip the hydronic system.

If you have a gas water heater add a small plate HX and a couple circulators. There may be some pre-built HX modules for this.

GroundUp

Electricity cost is directly relative to BTU and cost per kWh. Based on your location, and assuming this is a basement under heated space with proper insulation, I'd estimate your heat loss to be no higher than 5,000 BTU per hour on a design day. Ballpark figure with $.10/kWh power, maybe a couple hundred dollars per year. You can sub your actual rate to get a closer figure.

Regarding the electric resistance mat in lieu of the hydronic, I'd avoid that at all costs if embedded in the slab. When (not if) a cable decides to break, it's junk and can never be repaired without tearing up the entire slab. Hydronic leaves many options for future changes in heat source, and honestly does not cost much more at all upfront.

evelyntoronto

Really appreciate the responses — thanks, everyone!

I had considered an electrical in-floor system, but for reasons mentioned, particularly in terms of longevity, decided against. I’d also like to leave the option open to heat the hydronic system in the future with a different unit (e.g., air to water heat pump, assuming costs come down over the next 10-20y!).

Thanks again, all!