Water storage

So, I'm doing some very early thinking about the plumbing for my new cordwood cottage.  I have a 50-gallon hybrid water heater that came to me as a gift.  I will be on well water here in northern Maine.  Now, the water coming up from the wells around here is about 45f, maybe less in our long winters.  I am wondering whether I might interrupt the well feed to the water heater with a tank that might bring up the well water temp some five or ten degrees, or more, before it enters the water heater.  A thirty-gallon plastic water tank seems affordable.  They cost somewhere around $150.  A metal tank would be too pricey for my budget.  The tank would be within the heated space of the house (as will be the water heater).  Has anyone done something like this?  Am I being penny-wise and pound-foolish?  

Would the plastic tank be under pressure?

Yes.  I would have to ensure that the tank is sealed enough for the pressure from my well pump.

I think it will increase the energy needed to heat your living space.
That could be a cost savings if you heat your space with wood or solar.
If you heat your space with the same thing you heat your water with, then adding the extra tank won't save any money.

Small cabin, 400 sq.f. will be heated with a masonry bell heater.  Long Maine winter in the northern woods.

A plastic barrel/tank can’t handle normal plumbing pressure.  Putting your well pressure tank there will work.  Yes, it’s expensive but required for most well pump systems.

Yes, the pressure tank will be right there.  So, no plastic water tank due to pump pressure.  Ok, scratch that.  Thank you!

Spend the money to upgrade the pressure tank to the largest that you can fit/afford.

Scott, we are just two elderly pensioners on the plumbing.  I have heard it said to size the pressure tank "accordingly" though to this day I have not apprehended the explanation.  But if the water sitting in the pressure tank gains a few degrees, I will consider that  success.  If bigger is better, then it sounds like my solution here.  Thank you!

If it was me, I would run the feed between the well and the hot water heater through your masonry heater in a place where it would pick up plenty of heat, but not enough to boil. A copper coil perhaps with a branched off pressure relief valve if you are worried about it, but not needed if designed and placed correctly. William is right that there is no free lunch. It'll cost you energy somewhere to heat this water up.

Running the piping under the masonry stove is also being considered.  The masonry stove is a bell, tentatively sized at 2' wide x 4' high x 30' long.  I have not yet costed the amount of metal pipe that I would need, but it seems that upsizing the well pressure tank to the max permitted by its pump might be cheaper.  I also have a ton of pex lying around, but I am not sure that pex would absorb heat quick enough.

If you have plenty of PEX, I would just use that, but build a manifold that sends it through parallel runs.
At 30' it will have a long time to pick up heat.
Since your cabin design is 400 square feet, I'm guessing the bell is along the entire wall.

What do you plan on putting above the bell?
It's pretty high and narrow for sleeping on.
A row of windows perhaps?
It could be good place for the pressure tank.

Since you seem familiar with plumbing, consider sourcing old water heaters.
If they are not leaky, then they can become your storage.
Stripped of insulation, they could go right inside the bell.
Most are bigger than 4' , so they would need to be installed horizontally.
That would reduce the length of pipe you need by a bit.
They are also kind big , so they will reduce the space inside the bell, but if the bench is not a bell (uses ducts instead of a big hollow space) that could be another advantage.
4-5 tanks with 40 gallons each would be a great amount of water storage.


For summer time, a southern facing solar thermal water heater makes a lot of sense.
You can build them to work  in the winter as well,but given your space  heating plans, I would skip that extra compilation.

Actually, if the temperature remains consistent, your well water could be used for cooling the house during the summer, by running it through a fan coupled heat exchanger.
A heat pump water heater would do the same thing, but much slicker and probably more efficiently.

William, the masonry bell runs down the center, lengthwise, of the cabin.  The bell is, overall, two feet wide.  The outer skins are 8" rammed clay-rich earth, and the inner hollow is, of course, 8" wide.  So, if you imagine a rectangular, open-plan room, it is divided by the bell.  Sort of like a counter top.  There is a doorway in the bell for back-and-forth access.  The water heater, pressure tank, and well pump are in a utility area such that the masonry bell is right there.  We are only two older people.  We don't use much hot water, so we are going with the idea from R. Scott to use a decent-sized pressure tank that should pick up several degrees while the water is 'on deck' for the water heater.  The pex will likely be used to bring water to my sheep and pigs and the greenhouse.  

Another path.  Instead of warming all the water just warm a line thru it.  Then you don't need a pressure rated tank.

Here is the large scale example.  Start at 1 hour and 9 minutes in.

Thermal storage.

smaller scale storage.  Better if more vertical for stratification.

storage "tank" aka box

So you might want to change your thinking on this.