electric tankless water heater for heated driveway?

CBRob

in the planning phase of another heated driveway. The client is reluctant to give up the garage space for a gas boiler.
He just replaced his domestic water heaters with 2 gas 50 gallon heaters.

I think I need about 75000 btus give or take to meet the melt demand. I think that converts to 22000 watts

Anyone have much experience with electric hydronic snow melting?

If you have any lessons learned to share Id love to hear them.

STEVEusaPA

Isn't gonna work.

CBRob

Well I wont put too much more effort into researching this option then.
What is the primary reason for this being inadequate?

Karl Reynolds

Look into a Thermolec B-23 wall hung electric boiler.

CBRob

I need to figure out how to compare the cost of heat.. I pay about $1.00 per CCF nat gas

and about $.16 per kwhour for electric

time to google some calculator

STEVEusaPA

CBRob said:

Well I wont put too much more effort into researching this option then.
What is the primary reason for this being inadequate?

It won't keep up/recover, and it's just the wrong appliance for the application.

CBRob

STEVEusaPA said:

CBRob said:

Well I wont put too much more effort into researching this option then.
What is the primary reason for this being inadequate?

It won't keep up/recover, and it's just the wrong appliance for the application.

is this the case for a wall hung electric boiler too? Is there a wattage that will keep up with the demand of 75k btu per hour?

Karl Reynolds

If your load is 75,000 Btu/h the Thermolec B-23 is a 23kw boiler and will handle the load. It has a huge amp draw though at 95.8 amps.

Jamie Hall

Karl Reynolds said:

If your load is 75,000 Btu/h the Thermolec B-23 is a 23kw boiler and will handle the load. It has a huge amp draw though at 95.8 amps.

Bingo. And that's' at 240 volts. Will it work? Yes, if you can feed it that much power. For most residences, that's what's coming into the house to feed everything, so you're going to have to go to at least a 200 amp service entrance to get enough oomph to run the thing.

Perhaps more to the point -- it will cost you about $100 every time it snows...

STEVEusaPA

Are you sure about the 75k btu's? Doesn't seem like much area or you're not going to get it melted too quickly. Which level of snow melt are you going for?
I'd make sure of the calculation, and do a wall hung gas boiler. You can throw in a loop to dump some heat in the garage also.
95 amps has to generate a serious upgrade to the electrical system.

JUGHNE

IDK about the snow melt requirements, the 75K does sound low though.

In any event a 200 AMP service could handle the 95 amp heater IMO, especially if the hot water is NG. There is still cooking and dryer load to consider.

GroundUp

Anything is possible, but it's not going to be pretty. As others have mentioned, 75k sounds pretty suspect unless the driveway is only big enough to fit 2 cars. Tankless or boiler on electric, both will do the job but the tankless will require another pump (high pressure drop) and P/S piping which defeats the cost savings of a tankless. I've got a couple electric snowmelt systems out there using Electro boilers and they work just the same as a gas fired hydronic system- a BTU is a BTU. With that said, at $1/therm versus $.16/kwh you're looking at a cost of $4.69 for the same 100k BTU output on electric as $1.05 would get you on NG. If it gets used once a year, you're already money ahead with NG.

As much as I hate the idea of it, there are gas tankless WH units (like Takagi) that are considerably smaller than any wall hung gas boiler (that I've seen anyway) if space is that much of an issue, and would do the job. I'd still recommend a boiler though.

BillyO

Big mistake, don't waste your time and effort

GroundUp

BillyO said:

Big mistake, don't waste your time and effort

Why?

Zman

Attached is the sheet for conversion to and from any fuel.
At your altitude, a cubic foot of natural gas does not contain 1,000 btu of energy. It is probably more like 750. Xcel energy shows the multiplier on the bill. Fortunately they bill by the therm not CCF.
The electric will not pencil out from an energy cost point of view.

hot_rod

A tankless heater with glycol, hmmm, some serious pressure drop involved. You may not flow enough to get full output in a pumped system.

On a DHW application you have 45- 60 psi to work with. In a pumped system just the pumps delta P

Tankless heaters are designed for low flow rates and high delta, exactly opposite of how hydronics operate

How many square feet? How quickly do you want to melt? I think you want 100 btu per square foot to get much performance.

GroundUp

There are thousands of Stiebel Eltron and Takagi tankless WH marketed as "boilers" by a certain rebadge company and sold in a certain green big box store, currently heating glycol filled systems. Yes the pressure drop is incredible, but it does work. I actually have a 14.4 kw Stiebel tankless "boiler" in my shop as a backup that I bought and installed 12 years ago before I knew any better, with 40% EG and a single NRF-25 (no P/S) serving 7 loops of 1/2" in the slab. According to the flowmeters and delta when in operation, it is putting exactly 14.4 kw into the slab and will keep the shop 70 degrees when it's -30F outside. As dumb and defiant of logic as it sounds, they will perform. I actually bought another one for backup in my new garage, even knowing better now. It was slightly used and $1000 cheaper than a real boiler so for the once or twice a year it might get used, I'm okay with it.

Seisco is another one that used to be rebadged by the same company and the guy around here that was on scene before me installed hundreds of them, many still in operation. I just replaced a circ on one such system last week that's been untouched for 17 years as the sole heat source for a 3100 sq ft slab home with straight Cryo-Tek -100 in it at 55%.

Solid_Fuel_Man

Yes!

Can we PLEASE not make blanket statements like "it wont work".....

You can heat anything with electric resistance, it's just going to cost you big dollars relitive to pretty much anything else to do it here in America anyway.

But with enough kW anything is possible, just like a big enough gas line. I work on plenty of 50+ kW process heaters where any combustion is not feasible.

All that said, a wall hung boiler isnt very big, and snowmelt is generally done in high end homes. There has got to be a place to put the boiler other than the garage?

Rant over....sorry.....no I'm not!

Jamie Hall

And to add to @Solid_Fuel_Man 's comment -- there's no physical reason why a water heater won't work, either -- though I wouldn't recommend it -- provided you get the pumps and mixing right.

kcopp

If space is an issue and you are considering an electric boiler... why not just skip the tubing and go w/ electric warming cables?

Zman

We use this pretty often for small slabs and walkways where hydronic isn't practical. https://raychem.nvent.com/products/electromelt-self-regulating-heating-cable-0

For your example of 22,000 (yes you did the math right), on a 240 volt service you would need 22,000/240= 91.67 amps. Most 200 amp residential services do not have that kind of power to spare.

It is also worth noting that if you intend to turn the heat trace on when it is super cold out, the amps will probably spike to double that at startup. Raychem has a chart to assist with the sizing. You would probably need a 150 amp equipment rated breaker to handle the spike if you need to start the system at 0 degree outside temp.

GroundUp

kcopp said:

If space is an issue and you are considering an electric boiler... why not just skip the tubing and go w/ electric warming cables?

Because a break in a resistance cable kills the whole system and there's no way to find it. At least with hydronics a leak can be located and possibly repaired. If nothing else, that loop isolated.

Zman

GroundUp said:

kcopp said:

If space is an issue and you are considering an electric boiler... why not just skip the tubing and go w/ electric warming cables?

Because a break in a resistance cable kills the whole system and there's no way to find it. At least with hydronics a leak can be located and possibly repaired. If nothing else, that loop isolated.

A very valid point. This combined with the startup inrush current would be the argument against.
I have had good success with the commercial heat cable. The installations need to be meticulous and good rebar placement is critical.

CBRob

Thanks for all the information guys. Now Im equipped to inform the owner that its a no go on electric.

He was willing to melt a smaller area of the driveway to get by with electric, but not at that expense.

CBRob

Zman said:

We use this pretty often for small slabs and walkways where hydronic isn't practical. https://raychem.nvent.com/products/electromelt-self-regulating-heating-cable-0

For your example of 22,000 (yes you did the math right), on a 240 volt service you would need 22,000/240= 91.67 amps. Most 200 amp residential services do not have that kind of power to spare.

It is also worth noting that if you intend to turn the heat trace on when it is super cold out, the amps will probably spike to double that at startup. Raychem has a chart to assist with the sizing. You would probably need a 150 amp equipment rated breaker to handle the spike if you need to start the system at 0 degree outside temp.

Im gun shy of these heating systems lately..
had lots of failures on roof melt heat trace and that is expensive enough.
Id hate to get the call back for a failure in a concrete slab.

pecmsg

CBRob said:

Zman said:

We use this pretty often for small slabs and walkways where hydronic isn't practical. https://raychem.nvent.com/products/electromelt-self-regulating-heating-cable-0

For your example of 22,000 (yes you did the math right), on a 240 volt service you would need 22,000/240= 91.67 amps. Most 200 amp residential services do not have that kind of power to spare.

It is also worth noting that if you intend to turn the heat trace on when it is super cold out, the amps will probably spike to double that at startup. Raychem has a chart to assist with the sizing. You would probably need a 150 amp equipment rated breaker to handle the spike if you need to start the system at 0 degree outside temp.

Im gun shy of these heating systems lately..
had lots of failures on roof melt heat trace and that is expensive enough.
Id hate to get the call back for a failure in a concrete slab.

In 25 years of using Frost Tex, I've never had a failure!

ratio

Some heat trace cable is classified as Type MI. It's basically a ³/₈ copper pipe with minerals packed in around the conductor. It's quite …robust. The last I heard, it was the only type of heat cable that did not require GFCI protection.

Solid_Fuel_Man

I looked into electric snowmelt for asphalt driveway a few years back. The cable worked out to be more than the asphalt per square foot. Honestly, the idea of electric is simple, no frost protection, etc. But a failure = groundwork or worse.

Intplm.

@CBRob Get in touch with a company called Stiebel Eltron. There tech support should be able to steer you in the right direction.

Jamie Hall

The biggest problem for most residences -- other than the bill at the end of the month -- is getting enough power. Most residences simply don't have a big enough service entrance.

Intplm.

I agree @Jamie Hall Many of the type of water heater I am referring to above needs three 50 amp breakers. That's a lot !
My suggestion above, should help @CBRob in discovering what unit might work in his situation.
( I was on the phone with Stiebel Eltron the other day concerning another matter and this subject came up prompting my recent post.)

CBRob

Thanks for the help you guys.
Owner okayed a proper condensing boiler.