Should I switch to tankless?

[WestMIchigan]

I currently have a 21 year old AO Smith 50gal water heater feeding a 40gal generic electric water heater which feeds the whole house. There are 4 bathrooms/showers but generally no more than 3 are used at one time. Would switching to a Navien NPE-240A or similar actually same me propane over the course of a year? I would be going from propane being the primary but not my only source of heating water. I could have less than 120°F water coming out of the propane tank and still be heated by the electric but on average most of the initial heating would be propane. I am on a well that is about 200ft down so the water temp won't change much at all over the course of the year. After letting my water run for about 10 minutes my cold water temperature is 53°F. Does tankless make sense from a propane standpoint or shoud I keep my current propane/electric setup.

 

[Breplum]

clarification question first. the 21 y.o. AO Smith is the propane heater now?
It will be impossible for me to answer the annual cost saving questions since there are cost variables at every turn.
Around here, it is definitely cheaper to operate natural gas (while they still allow gas) vs. electric.
But propane, I can't contribute help.
I am a complete Navien NPE series fan boy.
But how about a hybrid electric WH? The prime downside is slow recovery and the tanks rot out, same as conventional.

 

[Sponsor]

 

[WestMIchigan]

clarification question first. the 21 y.o. AO Smith is the propane heater now?
It will be impossible for me to answer the annual cost saving questions since there are cost variables at every turn.
Around here, it is definitely cheaper to operate natural gas (while they still allow gas) vs. electric.
But propane, I can't contribute help.
I am a complete Navien NPE series fan boy.
But how about a hybrid electric WH? The prime downside is slow recovery and the tanks rot out, same as conventional.

Yes, the AO Smith is a 50 gallon propane. No natural gas around here. Not sure what I think of a hybrid electric. I have heard various pros and cons. This would be in a finished basement.

 

[Jadnashua]

A hybrid will somewhat act as an air conditioner...the heat it pulls from the air gets put into the tank. It's more efficient than just inserting it at a 1:1 ratio with a stock electric tank. Under a heavy load, the hybrid may revert to a stock electric tank, but when fully recovering after the flow stops, it should run in hybrid mode and be more efficient. Newer tanks are required to have more insulation, which helps with the standby losses.

If I follow you, you intend to use the tankless as a preheater for the electric tank? That has a chance of working, but using it as the primary heater with up to three showers in use at once, would not work well, IMHO.

 

[Breplum]

The Navien is pretty much as efficient as they come.
With propane, it is rated at 5.6 GPM with 67 degree temperature rise. So with your water coming in at 53 you would get up to 120 degree water delivered in insulated pipes.
If you figure out your shower head's flow, then that will indicate simultaneous showering conditions.
In my old 2017 Navien spec sheet, it quotes propane at $2.41/gallon and postulates 193 gallons/year for estimated operating cost of $465.

 

[Fitter30]

Gallon of lp 91,000 btu's need for to figger total cost with tax and delivery fees. Most condensing water heaters 96% efficient.
Total cost of electric per kw. Electric is 100% efficient. 3412.142 btu's per kw
25.6 kw = 87300 btu's (96%)
When having two water heaters piped in series the first heater catches most of the lime.

 

[WestMIchigan]

The Navien is pretty much as efficient as they come.
With propane, it is rated at 5.6 GPM with 67 degree temperature rise. So with your water coming in at 53 you would get up to 120 degree water delivered in insulated pipes.
If you figure out your shower head's flow, then that will indicate simultaneous showering conditions.
In my old 2017 Navien spec sheet, it quotes propane at $2.41/gallon and postulates 193 gallons/year for estimated operating cost of $465.

A hybrid will somewhat act as an air conditioner...the heat it pulls from the air gets put into the tank. It's more efficient than just inserting it at a 1:1 ratio with a stock electric tank. Under a heavy load, the hybrid may revert to a stock electric tank, but when fully recovering after the flow stops, it should run in hybrid mode and be more efficient. Newer tanks are required to have more insulation, which helps with the standby losses.

If I follow you, you intend to use the tankless as a preheater for the electric tank? That has a chance of working, but using it as the primary heater with up to three showers in use at once, would not work well, IMHO.

I wasn’t planning on having a tankless as a preheater. It was hoping for a single source solution. I knew it was marginal but I was hoping I had miscalculated somewhere. Installing two would require too much $$ to make it happen.

 

[Dana]

Yes, the AO Smith is a 50 gallon propane. No natural gas around here. Not sure what I think of a hybrid electric. I have heard various pros and cons. This would be in a finished basement.

In almost all local markets a heat pump water heater will have a lower operating cost than propane, usually even cheaper than natural gas.

During the summer months in any MI location a large fraction of the heat is pulling from the room would be the latent heat of vaporization of the water it is removing from the air. It's more similar to a dehumidifier than an air conditioner in that regard, but it will also sensibly cool the space by a small amount, and the drier air mitigates against "must basement" odors & mold growth. During winter when the indoor humidity levels are low the sensible cooling is a bit more than in the summer, but we're talking about 1F typical for a 800 square foot basement at moderate water use. If the basement is actively heated about 2/3 of the heat going into the water is drawn from the room, representing a modest heat load for the heating system.

So if the basement is currently being actively dehumidified or the house is air conditioned, a heat pump water heater will carry some of those loads, lowering the overall amount of energy used by the AC or dehumidifier- it's a net electricity use win. A dehumidifier takes the latent heat and creates warm air out of it putting sensible heat into the room- a heat pump water heater puts the heat into the water inside an insulated tank.

This market had matured considerably since the early days. Currently available heat pump /hybrid water heaters are 3rd or 4th generation designs, far superior to what was available a decade ago. Don't be distracted or put off by negative reviews or complaints from 5+ years ago on first & second generation goods, many of which did have issues. Newer versions are more efficient, quieter, and more reliable.

 

[Jeff H Young]

good point breplum, basicaly how long will burning gas be permited? and will they curb use with taxes or penalty? like 2.50 a gal propane get a 25 cent tax per gallon and then 50 and so on until it no longer a viable option . expected life of a water heating system? 10 years? so if you can save 50 bucks a year on heating water over 10 years 500 bucks not bad if you dont spend a ton on upgrading the system . I look at the yellow stickers the worst unit versus the most efficient seems to be a small differance like 70 bucks a year. Anyway let us know how the numbers come out how much in dollars and cents your hot water cost now and how much you expect to pay, cost to replace equiptment standard versus the super energy miser system. of cource its a bit of guesswork but Id sure like to know how much youll save

 

[WestMIchigan]

good point breplum, basicaly how long will burning gas be permited? and will they curb use with taxes or penalty? like 2.50 a gal propane get a 25 cent tax per gallon and then 50 and so on until it no longer a viable option . expected life of a water heating system? 10 years? so if you can save 50 bucks a year on heating water over 10 years 500 bucks not bad if you dont spend a ton on upgrading the system . I look at the yellow stickers the worst unit versus the most efficient seems to be a small differance like 70 bucks a year. Anyway let us know how the numbers come out how much in dollars and cents your hot water cost now and how much you expect to pay, cost to replace equiptment standard versus the super energy miser system. of cource its a bit of guesswork but Id sure like to know how much youll save

I can’t even begin to quantify my water heating costs. It isn’t the only appliance on propane and obviously electric is a guess also. With 4 kids 10-16 there are frequent showers, lots of laundry, and plenty of dishes being washed so water usage and actual costs are something I can’t even begin to guess at. I’ll have to look at the hybrids again. I have pretty much dismissed them.

 

[Jadnashua]

After a cold spell in western Michigan, I'd bet your incoming water could be close to freezing...I have measured that here in S NH (not far from Boston) after a cold spell in winter...your water from a tankless system then that might do fine in the summer, now could be 20-25 degrees colder at maximum output. They can work if you have modest needs or are willing to sacrifice and time share its use where it can get cold. My sister lives in Holland, and the incoming cold water there can be really frigid when I've visited in the winter. A long shower like many teens like means your going to cool the inlet pipes down to whatever is coming in from the street. How deep is your frost level? They don't usually dig the pipes much deeper because of the costs, so it's very possible to get as cold there as it does here.

Today's tanks are required to be much more efficient, mostly because of insulation, but burner design can help some, too. The heat pumps are more efficient and reliable, too. Depends somewhat on what your utility costs are when you figure your cost/BTU used. The extra insulation does drop the standby losses some, and depending on where the tank is located, those standby losses may help with space heating in the winter and may not be a big deal in the summer with cooling, depending on where it is located.

 

[WestMIchigan]

Question on the hybrid since they were brought up, it looks like the recovery rate is fairly slow. Looking at a Rheem

After a cold spell in western Michigan, I'd bet your incoming water could be close to freezing...I have measured that here in S NH (not far from Boston) after a cold spell in winter...your water from a tankless system then that might do fine in the summer, now could be 20-25 degrees colder at maximum output. They can work if you have modest needs or are willing to sacrifice and time share its use where it can get cold. My sister lives in Holland, and the incoming cold water there can be really frigid when I've visited in the winter. A long shower like many teens like means your going to cool the inlet pipes down to whatever is coming in from the street. How deep is your frost level? They don't usually dig the pipes much deeper because of the costs, so it's very possible to get as cold there as it does here.

Today's tanks are required to be much more efficient, mostly because of insulation, but burner design can help some, too. The heat pumps are more efficient and reliable, too. Depends somewhat on what your utility costs are when you figure your cost/BTU used. The extra insulation does drop the standby losses some, and depending on where the tank is located, those standby losses may help with space heating in the winter and may not be a big deal in the summer with cooling, depending on where it is located.

See my first post, I am on a well that is just over 200ft deep. My cold water temperature doesn't vary much at all. It varies based on the holding tank in an unfinished basement which is currently in the process of being fully insulated vs partially insulated now.

 

[Dana]

Question on the hybrid since they were brought up, it looks like the recovery rate is fairly slow. Looking at a Rheem


See my first post, I am on a well that is just over 200ft deep. My cold water temperature doesn't vary much at all. It varies based on the holding tank in an unfinished basement which is currently in the process of being fully insulated vs partially insulated now.

Hopefully you haven't fallen into the mold-risky pitfall of installing a fiber-insulated studwall (either tight to the foundation, or with an air gap), with an interior side vapor barrier. Basements are subject to both interior moisture drives and condensation inside the studwall in winter, and exterior moisture drives from ground water & high dew point summertime air. There are ways of doing it on the cheap without creating mold farms- a topic that gets covered fairly often on the remodel forum here.

With multiple teenagers taking showers the "apparent capacity" of any tank water heater (including heat pump water heaters) can be extended substantially using a drainwater heat exchanger to pre-heat the incoming water headed to both the cold side of the shower and the cold intake to the water heater. They're not cheap, but cheaper than the upcharge between a 50 gallon heat pump water heater and an 80 gallon version, and a 4" x 48" or bigger can cut the total energy use by about half or more. There are others.

Energy use alone won't pay for the heat exchanger if it's a heat pump water heater (it pays for itself up front by the reduced size), but it will pay off on energy use well before you're rid of your brat-pack if heating with propane or a plain old electric tank.

The current best-in-class (on both return efficiency and lower pressure drop) is the EcoDrain VT-1000 series, which can be purchased direct from the manufacturer. (I don't believe this Canadian vendor has distributors in the US yet). Renewability's Power Pipe series isn't bad either, and can be gotten through the big orange box store's website and a few other vendors, or direct from the manufacturer , also in Canada. (I installed an R4-48 4" x 48" PowerPipe installed at my house over a decade ago and it's still performing well, but were I doing it today I'd probably go with a VT-1000-4-54.) They are sometimes discounted direct from Renewabilty on the Am**** site, but lately they've been close to full-retail.

Being on a deep well is usually an argument against going tankless due to rapid liming of the heat exchangers. Some manufacturers will even void the warranty if the well water tests over some water hardness level. (If you have a water softening system that can be better controlled.) They can work even with hard water, but plumb in ports for annual de-liming if going that route. I've seen them go 10+ years without maintenance on well controlled municipal water systems, but at the other end of the scale some homes will need de-liming every six months.

 

[Reach4]

With multiple teenagers taking showers the "apparent capacity" of any tank water heater (including heat pump water heaters) can be extended substantially using a drainwater heat exchanger

That would be really effective for long and consecutive showers.

A heat pump water heater could spend a lot of time using more-expensive resistance heating with long and consecutive showers. Setting that WH to heat-pump-only could limit shower duration, which could be good, but would also call for spacing out the showers.

 

[Dana]

That would be really effective for long and consecutive showers.

A heat pump water heater could spend a lot of time using more-expensive resistance heating with long and consecutive showers. Setting that WH to heat-pump-only could limit shower duration, which could be good, but would also call for spacing out the showers.

Setting it to heat pump only when there are going to be 3+ consecutive showers would be the worst. Once depleted the recovery time is glacial- the kid has to be late for school or go to school smelly. It's better to have sufficient CAPACITY to serve up 4 showers of reasonable duration, especially if operating in heat-pump-only mode.

With a sufficiently large drainwater heat recovery unit, the rate at which hot water is drawn is reduced by 15-25% (even more for a really tall one), and the fact that the incoming water is already tepid means the recovery time to reach showering temp is cut in half. The tallest and fattest heat exchanger that reasonably fits is always the "right" one. If the water in the well is 55F and the temp at the showerhead is 105F, the water coming out of a 50% rated heat exchanger during showers would be about 75F at 2.5 gpm and warmer still at a 1.75-2 gpm flow. So even the water at the bottom of the tank when the output of the tank dips to 100F will already be half way there, and the average temp of the tank will be even closer to the 105F temp, assuming he heat pump started running as soon as the tank temp dropped below 125-130F (typical for a 140F storage temp setting on the water heater.)