Alternatives for high efficiency tank gas water heater

[Bcarlson78248]

My current 40 gallon gas water heater was installed in my basement in 1992, so its probably time for a replacement. I plan to do it as part of a larger renovation, so I have the opportunity to reconfigure things a little and look for higher efficiency.

Factors to consider
- I need a short water heater to match the existing flue pipe connection to the masonry chimney, but have space use a larger diameter water heater (e.g., go to a 50 gallon short).
- I don't think the existing gas connection would support a tankless, and it would require tearing up quite a bit of finished basement to upgrade the gas line.
- The utility room is large enough to provide the air volume needed for a Heat Pump water heater.
- Due to the other renovation changes, I could also switch from the existing metal flue into the chimney to a PVC flue and air intake that goes directly out the side wall.
- There is a floor drain almost right next to the water heater.
- I'm in the Washington DC area, so ground-water and air temps are cold, but not frigid.

The simplest replacement would be a new gas water heater, but the Energy Factor would be in the range of .58-.62. I've also looked at Heat Pump water heaters, Hybrid water heaters, and some gas models that advertise higher efficiency.

Any insight on reliable solutions that would work for a family of 2-4, and maybe gain some efficiency?

Thanks,

Bruce

 

[Phog]

Hi Bruce, with a family of 4 you might or might not see any cost benefit, going from gas to a hybrid heat pump/electric water heater. The heat pump is very efficient but also has very slow recovery, and with frequent hot water draws spaced throughout the day, the unit would likely be relying often on the backup electric heating element & thus defeating the cost savings from the heat pump. For times when there are only 2 building occupants that calculus could change.

In addition to your family's usage profile, the relative cost of course also depends on the utility rates in your area for electric vs. gas. Be aware that heat pump units are usually quite tall, although removing the flue connection may give you enough room to fit one in. Be sure to factor in the required free head room in addition to the unit's height if you are thinking of going this route.

If you're interested in increased efficiency with a gas appliance, your can move to either a power vent or condensing type tank & run plastic venting out the side of the house. Sticking with the masonry chimney basically limits you to an atmospheric vent system (aka what you already have), which is inherently inefficient because the pilot is always burning & because the continuous flue draft pulls heat out of the tank & conditioned air out of your house and sends it up the chimney 100% of the time, even in standby.

Power vent units fix both those issues. Condensing units do too, and also have the added benefit of pulling the latent heat of phase change out of the flue gases. They are therefore usually significantly more efficient. You do also need a nearby drain for condensing units, but it sounds like you already have that. There were some issues when condensing tanks first came out with premature failures, and as a result some plumbers still recommend against them. YMMV.

Some people still prefer the traditional atmospheric vent tank despite the more efficient options now available, because they have no moving parts to break down and are (in theory) the most reliable. The newer atmospheric vent tanks post-2015 are required to have thicker insulation than the old ones, and so are marginally more efficient than your 1994 tank. You would therefore see your monthly energy costs go down a little even by just going with the 2018 version of what you've already got.

Tankless do usually require upgrade of the supply line & often the gas meter as well.

Good luck!

 

[Sponsor]

 

[Dana]

The heat pump/hybrid water heater may be the right solution for you, but if 4 people are showering in rapid succession or a couple showers shortly after a tub-fill you will likely either need something bigger than 50 gallons, or a drainwater heat recovery unit to enhance the "apparent capacity" in showering mode.

But there may be another alternative:

Navien's NPE series condensing tankless water heaters are designed to work with 3/4" gas plumbing of surprisingly long distances, and might be directly retrofittable. I have no direct experience with those units, but it's in the specs. They prefer that it be the nearest big-burner load to the regulator if it's sharing a gas line with a furnace/boiler, etc.. The biggest one (NPE-240) can be installed with as much as 30' "equivalent feet" (equivalent lenghts of ells & tees) of distance between the regulator and the tankless. The NPE-180 can go as far as 50' (equivalent) and is fine for most 1-1/2 bath houses. The NPE 150 can go 70', but won't cut it for more than a single-bath.

I have no first-experience with the NPE water heaters, but they seem to be installing a lot of them in my area to replace plain-old tanks without upgrading the gas lines.

The heat pump/hybrid solution will remove a LOT of moisture out of the air during the summer and knock a degree or two off the average temperature in the utility room too, which is usually a good thing.

A Sanden heat pump water heater is a hefty hunk of change, (they run about four grand with an 83 gallon tank, $3750 with the 43 gallon, which might still be enough with the tank set to 150F+ for storage) but is more efficient than a tank-top compressor heat pump water heater, and more powerful. They recover faster, can store more heat per unit volume (a the higher storage temps possible) and the tank could be placed where the old one was. Even the shorty version of the 83 gallon tank is less than 59" tall, and the plumbing connections are all on the side. The compressor is mounted outdoors (looks a lot like mini-split compressor), but is a hermetically sealed CO2-refrigerant system- the connections between the outdoor unit and tank are only water plumbing- there are no refrigeration technicians involved in the installation.

The recovery time is as-fast or faster than a standard electric tank, and it can still make 170F water when it's -20F outside. (I saw a post from a guy in Cincinnati this morning happily reporting plenty of hot water capacity from his Sanden when it was -3F outside.) Unlike tank top heat pump water heaters a Sanden will neither cool nor dehumidify your house. There are a few people in the Pacific Northwest heating their houses with these things.

In case you're nervous about being a new-product guinea pig, the Sanden water heaters are on their third or fourth generation, a product originating out of Japan's "EcoCute" technology consortium of the early 2000s, and have been sold in significant quantities in Asia & Australia. The NEEA utility consortium in the Pacific Northwest began assessing them for the US markets about five or six years ago. It's a real product, with a real and largely favorable track record.

Sanyo was also part of the EcoCute consortium and used similar compressor technology for a space & hot water heating combi system marketed in Europe & Asia a decade ago, but have since pulled back from the space heating. I don't believe Sanyo ever sold products based on that technology in the US.

 

[Bcarlson78248]

I appreciate all the input. After a little more research on the hybrid heaters, it seems like they may not be a good choice because of the longer recovery time for the mid-priced units (those around $1,200-$1,500). I will continue to look at the NPE tankless also, although it would probably make the installation more complicated.

Based on a quick look at what Home Depot sells for standard gas water heaters, this one seems to be a good choice for a moderate upgrade (.66 energy factor) from what I have. https://www.homedepot.com/p/Rheem-P...TAR-Tank-Water-Heater-XG50S12DM40U0/204321571 They also sell a Richmond power vent model for about $150 more, but it doesn't have a better energy factor.

Bruce

 

[Clog]

The relatively rapid evolution of tankless water heaters have given me pause. The second aspect about tankless that pauses my adoption is that people are adding storage tanks to tankless systems, because the tankless alone wasn't doing the duty in their situation. The third tankless downer is that some people were adding multiple tankless units to serve larger homes/demands. If one is adding a tank, what is the point of tankless? And if one is adding multiple tankless units, that surely is a heavy capital expense upfront. By the time one is even a quarter of the way in recapturing that upfront expense in fuel burning savings over time... the tankless units might crap out and have to be replaced again?

From a property owner's perspective, I'm thinking that first step gains in improving water heating and delivery on demand efficiency would be to insulate ALL the hot water piping, especially those pipes that trawl under the house in the unconditioned crawl space.

In the last two water heater installations I've done, I tore the sheet rock off the walls to insulate the first 8 feet of both hot and cold leading to the heater. Local code requires first 5 feet be done anyway, so might as well insulate down to the bottom plate. I'm going to submarine into the crawl space of those two homes later and continue the insulation of every visible hot water pipe. During any kitchen or bath remodels, the wall pipes will get insulated. Last year, I redid the siding to a house, no plumbing involved, but I insulated the pipes anyway before replacing the WRB.

I know tankless is good, but I'm not convinced that tankless is THAT good yet, under all circumstances. But that could simply be from a lack of complete understanding about the choices available, which themselves seem to be ever changing. Keeping up with it all is kind of a tankless job.

 

[Jadnashua]

There is some simple physics to it all...how satisfied people tend to be with one is how cold their wintertime water supply is (bad for any volume or temp rise to a useful value), and how soft their water supply is. Hard water can quickly generate mineral deposits, decreasing the efficiency and throughput of the heat exchanger. Throw in the higher capital cost and maintenance requirements, plus the potential inability to keep it running on a warm water use (minimum firing rate), and it starts to be only looking good to certain people who have blinders on. There are situations where they work great. There are a lot where they don't. Depends on your pocketbook and tolerance level.

 

[WorthFlorida]

A heat pump water heater takes heat from the air to heat the water. If the water heater is in a unheated basement there is little heat in the air to extract. If the space is heated you're transferring heat from your furnace to the air then to the water. The by product is it will cool the space down, then reheat it with your furnace. Not very efficient. In VA in the summer, would would gain where your cooling the basement.

Where a heat pump water heater may shine is in garages in the southern states where freezing is not an issue. It is nothing but an air conditioner in reverse. It will cool the garage down and in the hot and humid southeast, it would be a blessing after putting the car in the garage with a hot engine.

 

[Dana]

A heat pump water heater takes heat from the air to heat the water. If the water heater is in a unheated basement there is little heat in the air to extract. If the space is heated you're transferring heat from your furnace to the air then to the water. The by product is it will cool the space down, then reheat it with your furnace. Not very efficient. In VA in the summer, would would gain where your cooling the basement.

Where a heat pump water heater may shine is in garages in the southern states where freezing is not an issue. It is nothing but an air conditioner in reverse. It will cool the garage down and in the hot and humid southeast, it would be a blessing after putting the car in the garage with a hot engine.

Heat pump water heaters in unheated basements are fine. It pulls heat through the slab from the subsoil in any location where subsoil temps are north of 45F, which is most of the continental US. Even in a fairly modestly sized basement it doesn't drop the room temperature by more than a degree or two.

Yes they will be pulling 2/3 of the heat via the heating system during the heating season if located in fully conditioned space, but the cost and efficiency of that heat varies:

In a house heated with a heat pump at a COP of 2.5 it will still be delivering heat leveraged by a heat pump, far more efficient than a plain old electric tank. The additional load to the typical house heat pump also increases it's average efficiency by a miniscule amount by increasing it's duty cycle.

If the heat is a gas furnace, the efficiency of that 2/3 drawn from the room is the same as the efficiency of the furnace, which in most cases is higher efficiency than a plain old standalone gas water heater. The standby losses of a heat pump water heater are a small fraction of those of a standard gas-fired tank, if only somewhat less than best-in-class condensing gas water heaters. It's still more efficient.

In a Virginia basement during the summer & shoulder seasons a primary benefit is the latent cooling / dehumidification it provides, keeping the "musty basement smell" at bay. Running a dehumidifier to keep basement humidity down converts that latent heat into sensible heat in the room air. Running a heat pump water heater converts that latent heat into sensible heat inside the insulated tank. The impact on room temperature is quite small, but the impact on room's humidity is significant.

There really is no down side to heat pump water heaters other than up-front cost, and slower recovery rates compared to gas-burners.

The Sanden heat pump water heater only takes heat from the outdoor air, not the house, which it does quite well (even at double-digits below 0F.)

 

[Phog]

Dana, do you know of presently available standalone heat pump water heat systems that are not integrated into a tank unit? The Geyser series from Nyle are the only ones I've ever heard of, and I can't find information about whether they're still made. It seems like a very sensible idea & could also be installed on any existing tank system, including gas. But for whatever reason they've never caught on.

 

[Dana]

The retrofit style heat pump water heaters were a tiny market even at their peak, and couldn't match the efficiency of second & third generation integrated heat pump water heaters. I'm not sure if anybody is still marketing them at this point, now that EF 3+ is the norm.

The standby losses of gas water heaters make them less suitable as a heat pump retrofit, but plain old electric tanks were pretty decent candidates.

 

[Phog]

I'm thinking more for the primary purpose of dehumidification. The Geyser units were overly expensive (in my opinion). But if there is something similar that is lower priced maybe it starts to make sense instead of a $200 Walmart dehumidifier. At least for a DIY install where I'm not paying a plumber.

 

[MrStop]

I don't know if you have made a decision yet or not, but I installed an HTP Phoenix water heater several years ago and that thing has been a beast. I have a family of 4 and it will easily handle consecutive or multiple showers at the same time. In my opinion, it performs much like a tankless unit, but without the reported drawbacks. One of the other benefits is that it pulls the combustion air from outside (like a high efficiency furnace), so it is a much safer gas appliance. You can check my history for a writeup on the installation.

 

[Jadnashua]

You're probably the only person here from Viet Nam...what may be available here, versus what's available there for purchase and maintenance, are probably two very different products.

 

[Bcarlson78248]

The HTP Phoenix is a very interesting product, but I'm not sure my hot water usage will justify the price difference for moving to that efficiency.

Bruce

 

[Dana]

The HTP Phoenix is a very interesting product, but I'm not sure my hot water usage will justify the price difference for moving to that efficiency.

Bruce

If you plan to live there a couple of decades, the Phoenix should last that long or longer, outliving the typical residential water heater by a factor or two or more. For short termers there's not enough "payback" to make financial sense in under 10 years.

 

[MACPLUMB]

Hi,
I'm looking for a tankless gas tank water heater. Where is the place I should find out ?

Check Paloma they are made in Japan so should be available to you, they also make some good rice cookers

 

[MrStop]

The HTP Phoenix is a very interesting product, but I'm not sure my hot water usage will justify the price difference for moving to that efficiency.

Bruce

Quite honestly, I haven't really seen much of a financial payback yet. It has pretty much allowed my son to take endless showers negating the efficiency. There might be some payback as, in theory, if I stay long enough that I won't have to replace as many water heaters.

My biggest criteria was more of getting the combustion air and fumes out of the house. It also allowed me to completely abandon the vent running through a wall I want to remove. Additionally, I wanted a good supply of hot water without the complexity of a proper tankless install. The heat pump electric water heaters didn't seem to have the recovery I was looking for at the time (not sure if that is still the case). The HTP was about in the neighborhood of the tankless or heat pump unit. In the grand scheme of things, it was more but didn't put me in the poor house.

 

[Dana]

The recovery rate of a heat pump water heater will never match that of even a plain old 50 gallon gas water heater, let alone even the smallest burner Phoenix. But a heat pump water heater would prevent the "endless shower" thing- even a 120 gallon version would eventually fall tepid.