I'm building a 4000 sqft house with concrete floors throughout.

I need a boiler or hot water heater to heat the radiant floors.

Because of my site, I can either do propane or electric. Propane costs are soaring. Electricity only costs 7.5 cents a kilowatt.

I'm thinking that I want to go all electric. Are there any electric boilers or hot water heaters that would work for a closed loop system?

 

Have you considered a biomass boiler - burning wood pellets or shelled corn?

 

Honestly - I haven't. I do a lot of traveling and want this to be both hassle free and economical.

 

Well if your gone most of the time it might not give you an ROI that you want

but

If your about the dwelling for days at a time when its cold, you could run the biomass boiler and the resistance boiler in a loop. piping and controls could be arranged so when the biomass boiler goes cold, the resistance boiler picks up the load. Bio mass is considerably less expensive to produce usable BTU - but comes with a lot of drama if you burn corn. Pellet fuel isn't as bad - but you still have to haul bags of fuel in - fill the appliance hopper daily or semi daily- and tend the contraption occasionally.

It becomes a hobby!

 

Sounds like it warms you twice.

 

Thermolec, Laing, Burnham and others make electric boilers. It sounds like you will need a very responsive system although you are designing just about the least responsive system going. It'll many days for the floors to recover.

Could you still design for a lower mass system with oversized panel rads?

 

Thanks for the recommendations.

I hear what you are saying response. Most of the spaces will have have passive solar loading to help during the day
.
When I travel - coming home may be an issue. Looking at being able to turn up the heat with my blackberry. If not, then the house will take a bit to warm up. One zone - guest rooms - will be turned on a day in advance of needing them...

 

Hi,

I'm having a little pipe dream (bad pun, sorry) about getting solar photovoltaic panels and using that power to drive an electric boiler. I would like to use the pre-existing natural gas boiler as a secondary unit. The idea is that a controller would use the electric boiler until some number of watts was consumed within a month. The controller would have a month by month set estimates of the # of watts that the PV panel will produce programmed into it. After the threshold was exceeded, then the controller would use the natural gas boiler. Using the utility company's gas is cheaper per BTU than their electricity.

As an aside, running the meter backwards doesn't pay because they buy watts from you at a much lower rate than they sell them to you. For my PV system, yes, the watts would go out in the daytime (for example) and come back through the meter at night. That's okay, because the utility company only reads the meter once a month. This allows me to use the house's connection to the electrical grid like a battery (that i don't have to buy, install, find space for, etc) to drive the electric boiler.

The electric boiler idea is attractive because I only spend about $30/month on electricity, which doesn't really pay for the PV very quickly. I spend WAY more on gas heating in the winter months (~$130/month). Seems like using the PV-generated electricity to do this would make sense.

Based on this thread, I checked out thermolec, electromn.com, ArgoElectric electric boilers. These all seem to be packaged as standalone boilers, with expansion tanks and controllers. Probably more stuff than I need since I already have a working boiler system. I really liked the EPR model by Laing (lainginc.com), but suspect it costs a zillion dollars because the stuff looks like a piece of art.

Has anyone got advice on a dual-boiler heating system like this? Seems like the limited doc on several of the boilers listed above allow for this possibility. I've read installation manuals for several models, but is there other general material on electric boilers that I should read? Any sense of how much a laing unit costs (still looking for vendors)? Would it be really hard to configure a controller to do this?

 

How much is your gas and how much is your electrical? Unless your electrical is cheaper per BTU for net heat, I wouldn't install the electric boiler. Really low overnight rates would be a reason to install one.

Otherwise, if gas is the cheaper way to heat your house do that and then let the PV cells offset the grid load. If you have more daily PV capacity than regular electrical capacity then you are going to turn the meter backwards in those rare no heat no ac months.

 

Hi Who,


Thanks for helping me work this out. I think I might be missing something, or I messed something up in my initial description.

My thought is that if I’m using photovoltaic solar panels for an electric boiler, the differential cost between a BTU of natural gas or electricity from the utility company doesn’t really matter (up to a point). I won’t be using them. I would be using my house’s tie to their grid as a bank, though. My utility company apparently does annual accounting for net metering (I thought it was monthly on my initial post), which is great because I can use credits for lots and lots of watts generated during the summer to run an electric boiler in the winter.

We don’t have overnight variation in electricity rates here.

I think it boils down (ooh, another pun…) to the fact that I cold generate watts (hopefully economically), but I can’t generate natural gas.

Does this sound right?

P.S. should I post this as a new thread to get more folks involved?

 

Unless you can get the PV set-up for free this will be a losing proposition.

Once you factor in the cost of the PV cells, the mounting, the inverters and all the wiring you will be far, far better off just burning the gas.

If you want to use the power of the sun then I suggest that you use fluid-filled solar collectors to directly heat the home.

 

Hi Furd,

Thanks for joining in. I think that going with gas absolutely makes sense in the short term, especially since it's in there and working (albeit old).

I'm starting to do all the calculations now. I'm using a web site (http://www.findsolar.com/proestimator/index.php) to help do a pseudo-reality check on my numbers--I'm in Colorado w/Xcel energy. The payback period is definitely on the order of ten years, but it doesn't seem like it needs to be free (don't get me wrong, that would be swell!).

I realize that the web site I'm using is motivated to sell these things, and that I shouldn't just be paying down the investment cost with savings on expected electric costs, but with expected natural gas costs (which I haven't figured out yet).

As far as figuring out the time needed to break even, it sounds like I really need to get a grip on the how many therms it takes to run my 30 year old natural gas boiler, how many watts it would take to run a possibly MUCH more efficient electric boiler, and compare those two costs.

I'm glad that folks are making sure I'm dialed into the big picture with the economics/business part of it, but I was still wondering if there was more plumbing related stuff that would be a problem or that I needed to get educated on. I figure that even if the economics don't pan out right now, I'll be ready when they do!

Thanks folks.

 

rviger... what a therm of gas cost and how much is each KWH or electrical? Answer that and I can explain numerically.

 

Hi again Who,

Here (and now), a therm is 57 cents and a KwH is around 12 cents.

Maybe the numbers will help me see the light of day on this!

Thanks for working the numbers.

 

Is that 57 cents per Therm the per-Therm cost on your gas bill or is it the average cost per Therm calculated from your total gas bill?

I think my per-Therm cost is about 77 cents but when the transportation charge, account charge, taxes and other charges are incorporated the average cost is close to $1.25 a Therm.

You need to do the same with the cost of your electricity, too.

Once you calculate your TRUE costs you can use this calculator to compare fuel costs.

http://www.warmair.com/html/fuel_cost_comparisons.htm

Remember that your gas and electric service are virtually maintenance free. The same cannot be said for a photovoltaic system.

 

Hi Furd,

I'll have to figure out the cost per cubic foot and look some more at the site you referenced.

Probably a good idea to clarify my numbers.

My therm cost per therm figure includes the "usage" the "pipeline," and the cost of the "natural gas" itself. I didn't include tax or the flat rate "service and facility." I just read these off of an old bill. The only other thing that could be relevant was a "therm multiplier," which I left out. It reduces the "measured usage" to yield the "therms used." Definitely a bit confusing.

One thing I did note on the therms was that the rate has gone up quite a bit since the bill I used. It's now 77 cents. Still way below what you've quoted but that's almost a 50% increase. If Who's already working with the 57 cent figure, that's fine.

For the electricity, I included all the extra fees (there's like over a dozen!). That number is still accurate because I used the average of two months.

Does this work for what we're talking about?

Thanks.

 

Consider the fact that a PV system of the size needed to provide 100% of the power needed to run an electric boiler (when the sun is out of course) is going to be a VERY large system... and VERY costly !

 

Okay so let's say 12 cents per kwh and 77 cents per therm.

For a $ worth of electric you get 1/0.12 or 8.33 KWH or 28,442 BTUs.

For a $ worth of NG you get 100,000/0.77 or 129,870 BTUs gross and if we assume your boiler's fairly inefficient, like 65% actual seasonal, then you are still getting 84,000 BTUs per dollar spent.

The NG is still 3x cheaper than electric for heating the house. Now if you put up some PVs, the first thing you would want to do is to lower the existing electrical load to zero, because your electrical energy is 3x costlier. Energy is energy, and the NG is that much cheaper.

To get enough PV to reduce your electric to zero and add on all the heat load would cost you a fortune...

Solar doesn't seem economically viable for most houses right now except domestic water preheating.

 

Natural gas is measured by cubic feet but sold by the Therm. One Therm is equal to 100,000 BTUs. Since natural gas does not have a constant heating value per cubic foot the gas is analyzed to determine its heating value and the metered consumption is multiplied by the "Therm multiplier" to arrive at the proper number of Therms consumed.

What this means is that you can ignore the volume (cubic feet) measurement and concentrate on the Therms measurement.

If you have a gas water heater, gas kitchen range or (natural) gas barbecue the consumption of all of these will contribute to the total gas consumption and it is a bit difficult to separate the gas used strictly for space heating from the total.


Your electricity may also have different rate schedules depending on how much power (kWH) you use during a billing cycle. This, along with the various charges for the energy and the transportation and distribution charges make this exercise a daunting one.

(I'm trying to keep the two threads separate in terms of my answers.)

 

Hi Who,

Wow. Thanks for those numbers. I think the big deal is that if I'm trying to calculate how many years it will take for such a PV system to pay for itself, I need to use the savings I would get on the natural gas solution. This means that my rate of paying off the PV is 1/3 the rate if I were already powering an electric boiler. Tripling the payoff period puts it at over 20 years, which is a bit much even for the most eco-idealistic of folks (at least for me).

Rats.

Just to get this out of my system, I’ll try to do a workup on the payback period of my hopeless idea based on all you folks have been telling me. Might be good so I can come back to this if gas costs continue to climb…

Thanks very much to everybody who’s chipped in. You’ve been amazing in entertaining something from way out in left field.

 

Thanks, Furd. Yeah, I'm definitely trying to keep from asking the same stuff in two places.

So on that web site, it's asking for cost per cubic foot of gas. I didn't know how to answer this because my billing quotes "measured usage," some funky "therm multiplier,' and an actual "therms used." Is the "measured usaged" somehow relatable to cubic feet?

 

A VERY rough approximation that is often used is that 100 cubic feet volume equals one Therm (100,000BTUs)

Some areas have natural gas that averages around 950 BTUs per cubic foot and other areas (mine, for example) average around 1050 BTUs per cubic foot.

Divide your real cost per Therm by 100 to get a cost per cubic foot to use. It won't be accurate but it will be in the ballpark.

 

While I'm a huge fan of solar, I don't see why, especially in sunny Colorado, you wouldn't just go directly to solar thermal space heating? Skip the whole electric boiler thing.

The efficiency of solar water heating is way way higher than the efficiency of PV. First cost is probably comparable, if not slightly in favor of thermal.

findsolar is pretty simplistic. If you really want to model PV performance, costs, etc., use the NREL Solar Advisor Model.

https://www.nrel.gov/analysis/sam/

Also, net metering laws are becoming more resident-friendly. e.g., my state has just gone to from monthly to annual. That helps.

 

Thanks for the improved web site for calculation, Xiphias. I'll take a look.

I think I should start to look at passive solar. Haven't really checked it out yet.

 

rv, can you now see why an electric boiler would be silly?

The payback on any investment to just reduce electric load is 3 times faster than reducing the heating load. That's because a $ of NG nets you 3 times as many BTUs as electrical resistance heating. Furthermore, after you have fully offset the regular annual electric load, the payback becomes 3 time longer for what you spend, plus that spending whose payback has just been tripled now needs an electrical boiler, a 200 or 400 amp service, and a major repipe and custom control.

The sun may burn out by the time that ever become a positive investment.

 

As for supplying to the grid, Ontario offers you the chance to set up a mini farm and sell it to them for 42 cents a KWH and I'm not sure many people can afford to take them up on their offer. Poor return for the risk, even at 4 times what we buy it for?

http://www.generationsolar.com/docs/soc.htm

That was 2 years ago that it started.

 

There is a nice solar estimator at http://www.find-solar.org -- also at http://www.solar-estimate.org It covers solar electric (PV), and solar water heating including pools and spas.

It includes all local solar incentives and local power utilities.

You can also place this estimator on your website .. nice.