I've seen a lot of talk about Marathon heaters on this board.  I hadn't heard of them before, but did some research.  They look good, but I have a couple questions - hopefully someone can help..

I like the idea of a non-metal tank with a lifetime warranty against leaks, but what is a real-life expectancy of the heating element?  If the heating element is going to go out after 10 years, the lifetime tank is kind of a moot point (maybe).

Along those lines, can the heating element be replaced?  With that lifetime tank, it would be nice if you could repair rather than replace the entire unit.

I've primarily looked at gas-fired heaters because the cost to operate estimates are so much higher for electrics.  Since I've started reading this board I've learned about the "false economy" of gas-fired heaters because they exhaust air that you've already paid to heat.  Makes sense, just never thought about it before. I'm wondering, again, about "real-world" costs & efficiency of electric vs. gas.

I'm pretty sure that we will do a drainwater heat recovery system - how should this affect my decision on which heater to choose?

Last - I don't think we're going to do PV solar right away, but I would like to do it at some point in the future.  Should that be a consideration when looking at gas vs. electric?

Thanks again for all of the help!!

Electric water heater elements are replaceable, it is a relatively easy DIY job, and they don't cost much.

good to know!  to me, this definitely adds to the value of the marathon.  thanks!

Heating elements for electric tanks are universally a standard replacement item.  I haven't looked at this with Marathon in particular, but they'd be crazy to have designed it without replaceable elements.

Don't overestimate the "false economy" of fossil burning water heaters. First, it's only for atmoshperic-drafted versions (direct-vent/sealed combustion use only outside air), and in most of the lower 48 of the US that unacknowleged cost is only 3-5% of the energy actually used for water heating. So, if you used the typical ~200therms of natural gas for water heating in a year, an atmospheric-drafted HW heater costs you another 6-10therms ($6-10, at current pricing in my neighborhood).  For propane (typically the priciest fossil-BTUs) that would be more like $15-35/year additional at current local pricing. But unless you're in nickel-per-kwh-land on electricity pricing a cheap fossil-fired atmospheric drafted NG tank will be cheaper to operate, even with the additional heat/ac loads factored in.

With drainwater heat recovery it means you can typically get away with lower capacity on your HW heater (both in storage volume and burner or heating-element rating.)  If you still need to fill bathtubs you need to size the HW heater to be able to do that reasonably. But for showers you'll need only roughly half to 2/3 what the rule-of-thumb sizing would otherwise dictate.

Solar thermal is usually more cost-effective than PV, and PV is a LOUSY way to support any thermal load (heating or hot water).  Best-in-class commercial PV efficiencies are only ~20% efficient at the panel, and lose some at the inverter, so by the time you've applied it to the stored water you're at 15-18% effiency BEST CASE.  By contrast solar thermal panels will typically deliver 50% + of the available incident energy to the thermal load. It'll vary with outdoor temp, but even when it's 0F out you can do better than 50% on 125F water with better flat-panels, and even more with evacuated tube:


There are some hybrid PV/thermal products out there too, which enhances the efficiency of PV in summer (they lose efficiency with heat- the water in the panel cools the PV to limit that loss.)  One such example is Sundrum:  http://www.sundrumsolar.com/index.php/products

great info, thanks!

to clarify, we are looking at possibly doing PV solar down the road not specifically for hot water, but a big enough system to provide a fair amount of our needs.  Right now the payback is just too long to justify, so my goal is to have the house wired for it so the install will be easier later.  When we get to that point, there's a good chance that solar thermal will be part of the project. 

 

I can't remember what are you planning on using for your primary heat? If you choose geo-thermal a de-super heater option would be good way to go. The best way to take advantage of that heat is with two tanks. For instance right now we have city water coming in and passing through the drain water heat recovery taking the city water from 55F to about 65F before hitting the first tank (a non powered electric 40 gallon tank) which is connected to the de-super heater or DSH from the geothermal. That tank then feed the main 50 gallon natural gas water heater, which has run a total of 24 hours in 19 months. If I had to do it again I would have gone with at least an 80 gallon pre tank and preferably a Marathon tank.

geothermal with desuperheater is the plan - sounds like we're planning a system very similar to what you have.  Just curious, do you know what temp increase you see in the buffer tank from the desuperheater?  Specifically in the winter, when you're in heating mode.

Why specifically a marathon tank?  Because it's not metal?

One thing that I remind my customers is to take the hardness of their water into consideration when buying a water heater and thinking of making it last. Also the need to drain ANY water heater is often overlooked. While I beleive marathon water heaters are great and will last, the elements can fall victim to very hard water like I have , just like a plain old lowes water heater can. They are very easy to fix though and I look at it like the brake pads on a nice luxury car. It's maintenance to make my luxury car last. The hard water is like the mountains you may or may not drive on. That said, I feel that a marathon is the best electric water heater on the market and the only one I deal with.

MY GUESS is that he would prefer a marathon because of it's supreme heat retention and it's an energy miser. :) Well that and they look kinda like a spaceship. lol

Honestly the marathon choice would be for the larger size foremost, the better insulation and never having to worry about it again.  Knowing me I will end up with an 85 gallon Fleet Farm tank that I will wrap in extra insulation   



Since our heat pump is water to water after the geo has run 4 hours we can see temps in the 140 range on the pre tank.  The thermostat I have on it max's out at 160 and on occasion it has passed that.  I know the DSH pump shuts off about the same temp and won't come on again until it is below about 120.

I have heard most DSH unit top out about 130F though, maybe because ours is water to water?

Kind of what I'm thinking too - I don't know if it makes sense to spend that much on a tank that will not be powered. 

Your comment about the buffer tank water temps is something I was JUST thinking about.  In reading about the efficiencies of a DSH in heating vs. cooling seasons & "stealing heat" - it seems to me that after a period of time, the temp from the DSH to the buffer tank should equalize, and then there really won't be much "stealing".  Is that a fair statement?

Yes for sure. As the water heats up in the pre tank it "steals" less and less heat from the system. For instance if we take a bunch of showers and the pre tanks is at 60F. In an hour with the geo running it might be 100F, up 40F in 1 hour. The next hour might get us from 100F to 130F and the next might get us from 130F to 140F. So less and less heat is being used or taken from the heat pump.

Either way it is the cheapest way for us to heat water. I suppose you could add a switch on the DSH pump if you wanted all the heat to go to the system and none being used to heat water. We have never had an issue with that since we are just heating water anyway.

The extra load to the system represented by the desuperheater is quite modest, and unless the geo design is very marginal (not likely- most are OVER designed), there would be scant benefit to switching off the DSH. Peak loads represented by hot water are large, but that's why you buffer it with a tank instead of going with a tankless. 

The thermal mass of the tank averages out that peak over time, at the expense of a modest standby loss.  As long as the DSH buffer tank is inside of conditioned space, during the heating season that standby loss all goes into heating the house anyway, so where's the loss? There is some efficiency losses to get it all the way to 140F, but it's a small fraction of the total load, and it's still a COP greater than 1.0  (which is the theoretical maximum COP you get with electric resistance heat in the Marathon, etc.)

Any concerns about the tank being plastic and any potentially dangerous compounds in it combining with the hot water? I know Marathons doesn't have BHA, but I wonder what else in plastics we will be warned about next. While people don't drink the hot water, showering in water laced with questionable plastic compounds might not be a good idea. I'm holding off buying one.

Not too much, with blow-molded polybutene:

http://www.gwelec.com/pdfs/MSDSnovoid224.PDF

Mold release-agents would be on the exterior of the tank, not the potable side. Polybute itself depolymerizes starting at 265C, which is way below the ~50C you'd be storing hot water at. 

If you love to worry,  worry about the hazardous chemical & biological contents of the water sources before it enters the tank.

Don't forget the value of not having to replace a leaking tank. They never leak at an opportune time. I remember mine going out on the morning of my wife's birthday. We spent the day moving the deep freeze in front of the access hole for the water heater and replacing it. She has never forgotten that birthday. We are building now and will have a large Marathon.

Marathon makes titanium heating elements for harsh water conditions that cause premature failure of conventional heating elements. When we bought our 85 gallon Marathon in April 2009, the advise Marathon gave me was to use the original heating elements and see how long they last. Can always replace them with the titanium elements later on if needed. Marathon also told me that softened water was much easier on the elements than hard water.  Here is a link that describes Marathons titanium elements (near the bottom of the page):

http://www.marathonheaters.com/cons_installtips.html

If you get 2 Marathons (1 used as a buffer tank) and they are the same size, you will already have spare heating elements at your disposal (just swap the elements between the unpowered tank and the powered tank.) We love our geothermal system with no buffer tank. If you haven't already read it, the geothermal thread "Justifying two electric hot water heaters" provides good information on buffered and non-buffered systems.

doesn't milk, OJ, water and many other things we drink come in plastic? the HW does not get to a boiling point to cook anything out

< Can always replace them with the titanium elements later on if needed. Marathon also told me that softened water was much easier on the elements than hard water.  Here is a link that describes Marathons titanium elements (near the bottom of the page):

http://www.marathonheaters.com/cons_installtips.html

I just came across this and was excited about the option of titanium elements as I have a marathon and have very hard water. I looked on the website but can't find any info online about the cost of these elements, anyone have any feedback? I swear this water heater is THE heater to get. I love ours and it works great.

I am unsure about pricing, but you can try calling Marathon directly. They may be able to sell you the elements directly. At a minimum, they should be able to tell you the suggested retail price. When I have called with technical questions, I have always spoken to a friendly, well informed person. They may be able to give you additional information (if any is available) on maintaining the titanium elements.   If you call, please let us know how you make out.