Dummies Guide to: Hot Water Jackets

Now that my rainwater tank is set to be delivered I’ve had a few more choices to make. The first is hot water. Some of these posts may be super detailed but I’m basically writing what I wish I could’ve read when I had to make these decisions. So many blogs/websites/articles start by assuming you have a clue about this stuff.  I like my building instructions the way I like my directions, based on the premise that I have no idea what you’re talking about…or where I am. So here it is, the unofficial ‘Dummies Guide to Tiny House Hot Water.’

Chapter 1: Hot Water Jackets

Ok so firstly, a quick run down on what I WANTED to do, before I get into what I’ll actually be doing. Originally I wanted to heat my water using the wood fired stove through a hot water jacket – also known as a wetback, although apparently that’s an American (and also a racist) term. This pretty much involves water running through a coil inside the stove, and heating the water when the fire is going.

The cold water runs out the bottom of the tank, through the jacket on the heater, heats up and rises back to the storage tank, where it pushes the cold water back through the cycle.  Taadaa!

domestic_hot_water_elmira

There are much more thorough and competent explanations of them online than I could offer (including lovely pictures like this one), here’s a good starting point. So without going into much more detail than that, here’s the list of things that made me change my mind and decide not to get the hot water jacket. If you’ve thought of them all then you’re already way ahead of me.

  • One of the biggest barriers was cost. I thought it would be efficient to heat water from a system I already own and will be using, but I’m just not sure that’s true when it comes to set up cost. My stove to start with was $1600, and not all stoves are made for hot water. The jacket itself is close to $300 and needs to be installed by a plumber, who would’ve had to cut holes in my stove to retrofit it. A new storage tank was over $1000 and that’s not including a header tank for overflow or pressure regulation.
    (Special note here, it took me about 15 years to find out that’s how much the tanks cost because there are secret code words for all of these parts and projects and it’s a whole new magical language. You can’t just look up ‘hot water storage tank’ because you’ll find all sorts of electric water heaters and tanks and get nowhere near close to the right thing. What you actually want is an ‘Open Vented Low Pressure Wet Back Hot Water Heater Stove Cylinder – Non Electric‘. I’m not even joking, googling this stuff is an art form in itself.)
  • I briefly looked at repurposing an electric water heater (a storage tank with an electric element inside it) and just not plugging it in so it would stay just a tank. But electric systems aren’t vented, meaning they don’t have a way to release the pressure and overflow of the water that would build up using the hot water jacket (more info on vented vs unvented here).
  • Electric heaters are also not designed for the high temperatures of a wood fired stove. Here’s another magic code word: vitreous enamel. This is what you want your storage tanks to be made from in order to withstand the heat your stove will create. Copper is apparently an option too but I couldn’t find many of those on offer anymore.
  • Even if you’re have a small system like I’ll have and won’t require that much hot water, you need to have a large storage tank  – sorry, ‘Cylinder – Non Electric’. There has to be enough space and capacity for your hot water to cycle through and cool down in the tank before it goes back through the stove. Once your fire is set to go, there’s no stopping the heat from boiling up that water. Hence the open vented and low pressure cylinder – I’ve been told things can explode. Not ideal. A large tank is an expensive purchase and you need somewhere to put it. Somewhere above your stove, which means mounted on a wall somewhere. Space is precious in a tiny so that was a big cross!
  • Putting the coil in reduces room in the stove, meaning a smaller fire box and therefore a smaller heater. This sends less heat into the house and into the oven for cooking.
  • If you don’t want to have your fire burning all year round you’re going to need a back up option. I figured instant gas would be a cheap and easy option – kinda wrong there. The cheapest gas options I found that would fit the bill come in at upwards of $600. The back up system also gets tricky because hot water jackets can’t run off mains pressure – meaning that connecting them to town water like most houses are won’t work. Gas systems, however, usually need a decent minimum amount of pressure to work. So running between two systems can be complicated. It probably means using a water pump – more equipment and more money.

There are also, obviously, lots of good reasons to use a hot water jacket to heat your water. If you already have the stove, live in colder climate and have a big enough house and water system then it makes total sense to piggy back off a wood heater to also heat your water. I love the idea of it, but sadly it just doesn’t make financial or practical sense for me to bother right now.

I’ll go into more detail on the pumps and gas systems and what I’ve chosen as an alternative in future chapters. If this hasn’t quenched your thirst for knowledge, here’s a super detailed article on water systems I found helpful for a number of reasons.  But for now – happy plumbing, fellow dummies! xx

-End of Chapter 1- 

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