I need to decide on a water heater this week. I was originally looking at the GE heat pump unit. Now, it looks like the Marathon may be the better choice. I live in a heating dominated climate (Milwaukee), so I'm not sure I'd see the benefits that GE claims. Any thoughts?

Posted By beckkl on 20 Jul 2010 11:16 AM
I need to decide on a water heater this week. I was originally looking at the GE heat pump unit. Now, it looks like the Marathon may be the better choice. I live in a heating dominated climate (Milwaukee), so I'm not sure I'd see the benefits that GE claims. Any thoughts?

With a hybrid half the heat going into the water is extracted from the room air.  If you're paying more per BTU for space heating than you pay for electricity (unlikely, but possible if you're heating with propane) it could be a net loss.  But if you're heating-BTUs cost less than resistance electricity, it's a net gain, even in the winter.

In the summer it's a clear net-gain, since the total amount of heat being dissipated inside the building's thermal envelope by the HW heater is roughly half what it would be for a Marathon, resulting in a lower air-conditioning load. (The COP of these beasties tends to run about 2-ish.)

But longer term it's still hard to say- there may be maintenance issues with the (compressor based, therefore mechanically more complex) hybrid that a (simple electric heating element) Marathon simply wouldn't have.  Time will tell, but I suspect the compressors will turn out to be relative low-maintenance- it's not much different from a home refrigerator compressor in size, complexity, or operating temperature, and it will have nice long duty-cycles with the thermal mass of a water tank to work with- it won't short-cycle itself into early failure.

But from a user convenience point of view, comparing the first-hour gallons numbers between them (which determines the number of showers you'll get out of it before a lengthy temperature recovery period) you may need a bigger heater than the GE hybrid.  If you're planning on 4 people showering all around the same time in the AM you may need more than the 63 first-hour gallons of the GE hybrid or the 61 first-hour gallons of the 50gallon Marathon. But for 2-3 people and low-flow shower heads & EnergyStar washers/dishwashers  either would be enough (unless one of those people is an endless-shower fanatic.)  Figure on ~12-15 gallons/shower for a 10 minute shower.  If you have a soaking-tub or 2+ people who prefer to tub bathe rather than shower, 60-65 first hour gallons is on the low side and you may have to schedule your hot water use at times.

I agree with Dana except for the COP (vs EF), which is around 2.6. It also has electric elements for when the heat pump can't keep up.

My electricity cost is currently $.126/kWh, and natural gas is about $1.00/therm. I put in a 96%AFUE furnace, so I'm guessing there is no way the GE model could be less efficient than the Marathon? Even so, does it still make sense to spend the extra $500 for the GE?

There is something to be said for simplicity, and the warranty of the Marathon. If the ROI on purchasing the GE over the Marathon is going to be 10 years+, I guess I'd rather have the unit that appears to require less maintenance.

Thanks for the input. I appreciate it.

Isn't there a tax credit on the GE?

Ah, you are correct. That brings the price down to about the same. Makes the decision easier. Thanks!

Looking at just summertime operating costs without the wintertime adder for the hybrid (or subtractor for the Marathon, etc. since half the standby loss supports the heating load):

12.6 cents/kwh is equivalent to ~29.3x 12.6= $3.69/therm

An electric tank with an EF of .95 (like a Marathon) then delivers a therm of heat to the water for $3.69/0.95= $3.88/therm

If the EF of the GE hybrid is ~ 2, the cost per therm delivered to the water in summer is $3.69/2= $1.85/therm

With a cheap old standing-pilot gas-fired HW heater running an EF of only 0.5, at $1/therm, it would deliver a therms of heat to the water at $1/0.5= $2.00/therm.

With a mid-efficiency gas tank HW heater with an EF of .60 you'd be looking at heating water at $1.67 therm...

...which is a lower operating cost than that of the GE hybrid.

For a higher efficiency power-vented tank with an EF of 0.7 you'd be at $1/0.7= $1.43/therm

...which is a substantially lower operating cost than the hybrid, half the cost of running a Marathon.

With on-demand/tankless heaters even though the EF numbers are inflated relative to real-world efficiency, you'd have even lower operating cost than with non-condensing tanks, but for substantially more up front money.

At your power & natural gas rates, why are you going with slow-recovery electric water heating?

Dana1,
Yikes, I hadn't been considering a gas tank heater. I'd like to do a PV system in a few years on the roof, and figured that on less gas appliance would be beneficial. I'm not sure that logic makes sense, being that I'll never be able to match the need of the entire house anyway. I'll have to take a closer look at some of the offerings.

Around here, there is a special interruptible rate for electric hot water heat that moves the GE from slightly better to much better than nat gas.

For some odd reason, on demand heaters are priced artificially high in this country.

You might as well use the actual EF of the GE at 2.35 - which makes it equal to nat gas in beckkl's case.

Wouldn't placement of the water heater also be a factor in the decision? For example if I place a GE hybrid in the conditioned attic then it lessens the load on my AC in the summer (but I'm in a hot climate). But from what I've read the hybrid can be beneficial in a cold climate too, for example in a basement, where it can reduce humidity. On the other hand if you have it in your living space (laundry room, kitchen closet, for example) then I guess it would increase your winter heating load?

I'm looking more closely at the hybrid. The skill set in my area to install and maintain a desuperheater on my central AC compressor just isn't there. But we're sort of on the verge of being higher demand (only 3 people in the house, but one is a tub soaker, and there is also a double-headed shower in the master). Do they make more than one size of the hybrid?

I really can't see any reason someone with inexpensive piped natural gas would consider a heatpump water heater. Running a heat pump water heater off of PV panels is even worse, you'll get far better efficiency just using solar water heating panels. Go with a natural gas water heater and you'll save money upfront, save money on water heating bills, and get better performance (better recovery rate).

Yeah, I was way off on this. I think I'm going to order the A.O. Smith Effex in a 50 gallon. Has anyone looked at the AO Smith "Hybrid" Gas On Demand? Supposedly it has no minimum flow rates and you can vent with PVC:

HYB-90N:

Posted By Jelly on 20 Jul 2010 10:37 PM
Wouldn't placement of the water heater also be a factor in the decision? For example if I place a GE hybrid in the conditioned attic then it lessens the load on my AC in the summer (but I'm in a hot climate). But from what I've read the hybrid can be beneficial in a cold climate too, for example in a basement, where it can reduce humidity. On the other hand if you have it in your living space (laundry room, kitchen closet, for example) then I guess it would increase your winter heating load?

I'm looking more closely at the hybrid. The skill set in my area to install and maintain a desuperheater on my central AC compressor just isn't there. But we're sort of on the verge of being higher demand (only 3 people in the house, but one is a tub soaker, and there is also a double-headed shower in the master). Do they make more than one size of the hybrid?

It's still a net power consumer, and while it might unfavorably chill a small enclosed space, the net effect on space heating load to the building is probably close to zero. Whether it appears as a true space heating load depends on how much heat is given up to the house in standby + hot water distribution plumbing losses + heat released to the house from drain plumbing before it exits the thermal envelope.  In a typical house something on the order of 15% of the total HW heat energy is abandoned in distribution plumbing but inside the thermal envelope. Another double-digit percentage would be given up to the house at the shower/tub/washer/dishwasher before it hits the drain.  A smaller amount is dissipated in drain plumbing, but it all adds up.  If roughly half the heat ends up staying within the structure, it's a net-zero heating load.

GE only makes a 50 gallon hybrid, Rheem has both 40 & 50 gallon versions, and there are 80 gallon hybrids from other vendors, but their first-hour gallons ratings only hit the low 70s. (See:  http://www.energystar.gov/index.cfm?fuseaction=heat_pump.display_products_pdf )  But since you're in a warm-water area you have several more first-hour gallons than advertised, since the standard incoming water temp for the rating test is 58F,  which is lower than is typical in LA, but you may opt for a lower storage temp than the standard too, giving up some first-hour gallons. (First hour gallons tests use a storage temp of 135F, incoming water at 58F, and a draw rate of 3gallons per minute, and measures the volume that can be drawn until the water temp drops to 110F. Large real-world draws such as tub filling are quite different from the test procedure.)  A drainwater heat recovery heat exchanger would roughly double the first-hour gallons for your super-soaker double headed shower, but would be of no aid in filling oversized tubs.

Posted By beckkl on 21 Jul 2010 10:06 AM
Yeah, I was way off on this. I think I'm going to order the A.O. Smith Effex in a 50 gallon. Has anyone looked at the AO Smith "Hybrid" Gas On Demand? Supposedly it has no minimum flow rates and you can vent with PVC:

HYB-90N:

The small condensing mini-tank on-demand gas hybrids (there are several out there now) can be a good option, because while they have some standby loss, storage temps are usually time-of-day programmable, and the mass of the tank avoids short-cycling losses & startup lags that occur with standard tankless on-demandeswhen used with high-efficiency washers that typically fill using short low-volume draws rather than a single larger one. While they might break 0.9 in an EF test, real-world performance of tankless on-demands are typically 6-10% lower than tested, but the hybrids should pretty much hit their numbers in actual use, with maybe a low single-digit percentage lower than tested for low volume users. (The standby loss is a constant, independent of volume used, but there are no short-cycling losses with a hybrid.)

I suppose I'd just have to figure if the extra efficiency justifies the $1K extra. Something tells me the ROI would be pretty long, vs. the effex. We do have a whirlpool going in though, and it may be necessary.

Posted By beckkl on 21 Jul 2010 11:57 AM
I suppose I'd just have to figure if the extra efficiency justifies the $1K extra. Something tells me the ROI would be pretty long, vs. the effex. We do have a whirlpool going in though, and it may be necessary.

If you have a truly large tub (75 gallons+) you'll NEVER fill it with an electric tank of reasonable size,  but tubs of almost any size are easily handled by a 140KBTU+ gas-burning on-demand.

When buying a big-burner gas water heater, be sure that both the distributor & installers in your area fully support it.  Installation is significantly more complicated than the typical 35KBTU/hr tank heater- it's more comparable to the installation of a condensing gas boiler used in space heating which is another option you might consider.  Hydro-air coils in air handlers are easily run at condensing temps, and having both AC and heating coils in the same air handler is common.  A 100BTU/hr boiler + an indirect 40 gallon tank (or reverse-indirect buffer/HW heater like an Ergomax E23 or the smallest TurboMax) would have over 150 first-hour gallon capacity on the hot water end, and is likely to be sufficient heating capacity for any moderate to high-R house in the midwest.  Condensing furnaces are pretty cheap, but if you're talking about a super-expensive water heater with a burner big enough to heat the house when it's -30F outside, a combi might make more sense.  The installed cost of a 100KBTU condensing boiler just isn't that different from that of a condensing HW heater, and heating contractors are likely to be more familiar with setting up boilers & indirects than most plumbers are with setting up on-demands.  (But if the heating system is already in place, forget about it- don't look back.)

Dana1,

The water overflow capacity is only 55 gallons, so I'd think I could fill it fine with the 50 gallon AO Smith Effex. Its first hour rating is 81 gallons. The whirlpool also has an inline heater.

As for the condensing furnace, why wouldn't I go with the A.O. smith vertex direct vent? It has a first hour rating of 127 gallons, and runs about $1500.

It looks like the price difference between the .62 Models and .70 models is too great. The ROI, from what I can tell is over 20 years. I can get a Bradford White .62 model for over $400 less. I'm just gonna pull the trigger and be done with it.

Posted By beckkl on 21 Jul 2010 12:55 PM
Dana1,

The water overflow capacity is only 55 gallons, so I'd think I could fill it fine with the 50 gallon AO Smith Effex. Its first hour rating is 81 gallons. The whirlpool also has an inline heater.

As for the condensing furnace, why wouldn't I go with the A.O. smith vertex direct vent? It has a first hour rating of 127 gallons, and runs about $1500.

A Vertex also has a fairly big burner- the installed price can sometimes run as high as 2x the cost of the unit itself if the additional burner power means the gas plumbing needs upgrading.  If the burner on the furnace is under 100KBTU/hr you're probably good to go, but if it's 200K you may run out of regulator/meter.

Either way, be sure that the distribution lines to the Vertex are fat enough to deliver the full 76KBTU/hr with margin, and that other large appliances aren't teed off from that feed line.  Discuss the supply line issues with the installer BEFORE, to make sure they're on top of it.  With half-inch line you don't even get 20' (with no elbows, since every 90 degree turn counts for 5' of length) before you're toast on the Vertex- it'll likely need to be 3/4" or 1" gas lines, tied in right at the meter/regulator to run reliably:

 http://www.industrial-equipment.biz/assets/images/information/gas-natural-piping.jpg

Bigger burner on-demands typically require 1" or 1-1/4" gas plumbing, and modulating burners tend to be more sensitive to pressure pulses than bang-bang/on-off burners like the Vertex, but when in doubt, oversize the gas lines.  Some states require extra certification for gas-fitters to prove they can to the arithmetic, others don't.  Stories of problems with undersized gas lines being installed for big-burner HW heaters abound- don't star in that movie if you can avoid it.  Most "standard construction" setups for gas fired HW heaters are half-inch lines, often teed off from the feeder lines from the furnace, which would be a recipe for trouble with a 76KBTU burner. (The HW heater could have issues itself, or cause problems with the burner on the furnace in that configuration.)

The Effex will probably leave you wanting- the 81 first HOUR gallons are at 3gpm, but you'll likely want a much faster fill rate- faster than 12-15 minutes.   At a healthy 8gpm fill rate it only takes ~ 6 minutes to fill the tub, but the temp of the water will be on the tepid side if you do since there will be inevitable mixing of incoming water.  For fast tub fills you really want to know is the first FIVE MINUTE gallons rating (which isn't tested for), but it's on the order of ~2/3 of the total storage volume. With only (0.8 x 40K=) 32KBTU/hr applied to the incoming cool water stream it'll likely leave you 10+ gallons short of a tub unless you wait another 6-10 minutes for the tank to recover to an acceptable temp.

With the 76KBTU/90%+ burner of the Vertex you'll be way ahead of the game compared to the modest 40KBTU/80% burner of the Effex, delivering more than twice the heat to the incoming water.  (In warmwater days of summer a 76K condensing burner on the Vertex would likely deliver 2-3gpm of 110F water for hours or days on end, but the Effex wouldn't.)  In a fast-fill of a 50 gallon tub you won't have to dial it back to let the burner catch up- it'll make it with some margin.  There's probably a higher subsidy available for the Vertex & Vertex 100 (the 100KBTU/hr burner version) than for the Effex as well.
 

Dana, I'm not sure if this private message system works - trying to get a message to you...