Immense electricity usage!

Shanew8869

Hey all, 
Dumb DIYer here hoping to get some insight.   I've just installed a hydronic radiant floor system in my small 800 sqft cottage.  The system itself has been working great.  Even at 55 degrees in the thermostat it's quite cozy in there.  Due to limited space in using a tankless on demand water heater.  (Ecosmart eco 11).  It's a slab foundation which we are tiling over.  I had radiantec company crunch the numbers and design the system.  I installed on site.  Sad part is,  my first full month with it running racked up about 2700 kWh to the tune of $1000 electric bill.  Where would you suggest starting to optimize this system or am I stuck with a system that's too expensive to run?

mattmia2

So what are you using for the boiler for this, or is the electric water heater what you are trying to use as an electric boiler?

Hot_water_fan

Where you located? What other electric appliances do you use? Is the slab insulated underneath? Sharing the Radiantec heat loss and design would be useful.

Shanew8869

It is an older house so I have to assume that the slab is not insulated underneath.  There is a reflective insulation on top of the slab with the tubing on top of that.  Located in rhode island. The on demand heater is being used as the boiler. I kept reading how they are good for radiant floor because they are designed to heat water to lower temperatures.  I wanted to eliminate the need for a large tank,  space is a premium.  I forgot to mention it is a closed system running glycol. 2 zones. (2) 250' loops and one 180' loop. The house is currently under renovation. The only other electric being used is led lighting and a water softener. 

Shanew8869

Also fluid temp going into the heater was around 95° coming out around 112°. 3 speed grundfos pumps running on low

Jamie Hall

My first reaction is "welcome to the wonderful world of electric resistance heat" -- for that is what your system is; its just that the heat generated by the water heater (by resistance) is transferred by water to your floor.

Now as to whether it's out of line, we need to know your electricity rate, and also at least an estimate of the heat loss of your building.

For perspective, your electricity usage is equivalent to about 65 gallons of heating oil, or about $400 worth of oil at today's prices in my location.

ethicalpaul

On the bright side, it's 100% efficient, but it's 100% efficiently using an expensive resource. If you can get a heat pump in there you can be 300-400% efficient

Hot_water_fan

It is an older house so I have to assume that the slab is not insulated underneath. There is a reflective insulation on top of the slab with the tubing on top of that. Located in rhode island. The on demand heater is being used as the boiler. I kept reading how they are good for radiant floor because they are designed to heat water to lower temperatures. I wanted to eliminate the need for a large tank, space is a premium. I forgot to mention it is a closed system running glycol. 2 zones. (2) 250' loops and one 180' loop. The house is currently under renovation. The only other electric being used is led lighting and a water softener.

Gotcha - you have a leaky, poorly insulated cottage, expensive electricity rates, and an inefficient resistance heater unfortunately. If insulation and air sealing is part of the renovations, you'll be in a better spot. The reflective insulation isn't doing much of anything, so you're heating the ground right now.

I kept reading how they are good for radiant floor because they are designed to heat water to lower temperatures

Unfortunately, that was a lie.

Shanew8869

That's the feeling I've been getting.  There is definitely more insulating and stealing to do,  floor isn't completely tiled yet either, so it'll get a little bit better... but yeah, I appreciate the insight. Good thing I got a wood stove going in too!

Hot_water_fan

With a heat loss in the 25-30,000 btu range, you should have plenty of room for improvement! 

GGross

Resistance heat is 100% efficient technically, you can't increase the efficiency of your heat source. To lower your heating costs you could, insulate the building, replace windows and doors, or lower the thermostat setting in the house. Beyond that you could see about lowering your per unit price for electric though that is likely not a possibility. If you have in-floor heat and you don't have good insulation for the slab (bubble foil does not do anything), I fear you will always be heating the ground and thus wasting fuel.

I know that is not what you wanted to hear, best of luck out there

Shanew8869

Shanew8869

These are some figures from radiantec for any interested parties.  Live and learn I guess. 

Zman

Is the room temperature fairly stable or does it tend to over/undershoot with the heating cycle?

Shanew8869

Temp inside is pretty stable.  But a couple walls have no insulation, no drywall.  One double pane window has a broken pane. Single pane glass in the doors.  So I still have work to do. 

Hot_water_fan

You’re on your way - certainly a motivating bill 

MaxMercy

Straight electric (resistance) is by far the most expensive way to heat. As you've been told,it's 100% efficient but the "fuel" is costly. As Paul said, a heat pump will get you over 100%. How can you get over 100%? Well, you're not but by using the waste heat that's in the outside air (there's plenty of heat in 30F air) or ground water, your KWH of electricity can do more than just turn to heat.

The on-demand water heater is a simple device, so you won't have any maintenance costs, but it's just the worst way of heating a home cost wise.

Long Beach Ed

Depending on where you live, your state may offer cash incentives for the 𝘴𝘮𝘢𝘳𝘵 folks who convert to 100% electric heating. They say you are saving the planet.

mattmia2

square footage isn't a heat loss calculation.

GGross

@mattmia2
Yeah Radiantec does that all the time, they shouldn't even put the estimate on the page. I think many building departments don't care enough to call it out but locally they have been denied a permit every time as it is not a manual J. They usually just send them to me because they know I will do it for them

hot_rod

Under slab and slab edge is where all the heat is going. Can you find some way to insulate the edge, that would be a huge improvement.

Is a small LP water heater an option? Here is a calculator to compare energy costs.

coalpail.com/fuel-comparison-calculator-home-heating

bburd

Some electric utilities offer lower rates  for electric space heating customers. You might check with them to see if you are on the correct rate for your system.

yellowdog

welcome to another botched radiantec system