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Pedro -Dawn- · 07-03-2022, 06:06

Hello All!

I am looking into tapping into my engine coolant system and create a very, very DIY system. This needs to be as low budget as possible. Attached is a very rudimentary drawing. “Boiler” tank is 18L. In am thinking of distributing already mixed water to my sink and shower, thus the thermostatic valve as the outlet to the hot water tank.

Some questions I have about this are:

- Instead of flowing the tank water through the heat exchanger, would you add a cooper coil ruuning through a reservoir, flowing coolant through the exchanger? Would this net any pressure in the current system?
- Do I need an expansion tank?
- Do I need a check valve?
- Do I need an extra water pump? I am thinking that the main pump would be enough

Any comments or suggestions you may have will be greatly appreciated.

Cheers,

Pedro

glenn.225 · 07-03-2022, 12:32

Well for a really simple DIY system all you need is is a coil of 1/2" or 5/8" copper, say six feet inside your “Boiler” tank.

This coil will be plumbed from your engine coolant system just like the heater core of your car.

It will heat the water as the engine runs. The thermostatic valve on the outlet to the hot water tank is a good idea but not needed if you are the only one using system and know the water maybe Hot.

Water in a small tank is not going to expand much with heating and you really don't need much extra.

Bearing in mind you have the manual skills and knowledge to make this system and already have a pressurized domestic water system it should cost very little.

That said drinking engine coolant will kill you so be careful of want you do.

Pedro -Dawn- · 07-03-2022, 16:11

Quote:

Originally Posted by glenn.225

Well for a really simple DIY system all you need is is a coil of 1/2" or 5/8" copper, say six feet inside your “Boiler” tank.

This coil will be plumbed from your engine coolant system just like the heater core of your car.

It will heat the water as the engine runs. The thermostatic valve on the outlet to the hot water tank is a good idea but not needed if you are the only one using system and know the water maybe Hot.

Water in a small tank is not going to expand much with heating and you really don't need much extra.

Bearing in mind you have the manual skills and knowledge to make this system and already have a pressurized domestic water system it should cost very little.

That said drinking engine coolant will kill you so be careful of want you do.

Hi Glenn, thank you for the inputs!!

I was skeptical about tapping straight into the coolant system. I thought that running through a heat exchanger would limit the distance traveled by the coolant, as well as isolate both systems.

Awesome knowledge about the heat<>expansion stuff. I couldn't find info on that and was a bit worried. So I'm guessing one less problem!

Cheers!
Pedro

leboyd · 07-03-2022, 20:50

I can’t see/read the plan very well, but as Glenn says you’re better off separating the systems. The coolant system requires high pressure to work properly (which is why you don’t open the radiator cap when hot). Therefore, you can’t open the system if it’s hot to shower. Use the coolant system plumbing to heat the separate system of lower-pressure potable water. (If your design is like this already and I just can’t see/read it, then you can ignore ��).

Uncle Bob · 07-03-2022, 21:03

Quote:

Originally Posted by Pedro -Dawn-

Hi Glenn, thank you for the inputs!!

I was skeptical about tapping straight into the coolant system. I thought that running through a heat exchanger would limit the distance traveled by the coolant, as well as isolate both systems.

Awesome knowledge about the heat<>expansion stuff. I couldn't find info on that and was a bit worried. So I'm guessing one less problem!

Cheers!
Pedro

Pedro, right on and if you wanted to refine it even further then a second coil in the tank connected to the potable water supply to heat the water with an expansion valve dumping into the tank completely eliminates any contamination issues. The tank is filled with water and has an overflow hose located to the top, meaning the tank is full of hot water at nil pressure and the water that you use is heated via the second coil in the tank. Lasts a long time before wearing out.

realem · 08-03-2022, 13:57

I found a small heat exchanger holds about a quart but will keep heating water for a quick shower while the engine is running. both house water and coolant run together through the exchanger. below link is similar
https://www.ebay.com/itm/29482075711...UAAOSw87RiD82t

two-rocks · 08-03-2022, 14:20

Not sure how a cheap water is not better (and cheaper), but anyway...

The heat exchanger should be fairly small as far as BTU's are concerned - the coolant tap from the engine may bypass the thermostat (I think mine does). I have a hydro-air heating system on my boat bypassing the engine completely (DIY not cheap) and found the water heater does not remove as many BTU's from the coolant loop as you might think. (i.e. takes time to warm the water in the water heater).

Dooglas · 08-03-2022, 14:26

Quote:

Originally Posted by two-rocks

Not sure how a cheap water [heater] is not better (and cheaper), but anyway...

My thought as well.

zstine · 08-03-2022, 14:57

the OP system may work but almost certainly more money and complexity than a standard off the shelf heater. He's got a separate heat exchanger, a circulation pump, a tank, and a thermostatic valve and then bits and bobs to connect it together. Yes, it will probably work, maybe not well(?), but for under $300 bucks you can get a tank with a heat exchanger inside and be done. No extra pumps or valves to fail or consume power. Why spend more and get less?

misfits · 08-03-2022, 15:32

You will need, highly recommend a pressure/temp relief valve on the tank side of the heat exchanger & one for the tank itself. Putting a mixing valve on the domestic side, odds are you will need an expansion tank. Especially once you put the check valve on the cold water inlet to the tank which I'd highly recommend. The circulating pump for the heat exchanger; not sure what you plan on using but keep in mind eventually it will be pumping water at whatever temp the loop off your engine produces. This doesn't include whatever the delta t loss is through the passes on your heat exchanger which is typically 20 degrees F.

captstu · 08-03-2022, 16:49

I installed a "tempering" valve on the domestic output of the hot water heater - it blends cold water to maintain a hot, but not scalding, temperature as the hot water heater cools with use.

You could turn it down a bit to be just warmer and run a single line at a warm temperature - but I think you will miss cold tap water for drinking and cooking.

The tempering valve comes from Amazon:

https://smile.amazon.com/Thermostati...dDbGljaz10cnVl

Bent Bugle · 08-03-2022, 18:57

I'td probably work - I'd definitely put a PTR valve on the tank, much safer, & a a non-return valve on the tank c/w inlet, must say it'd be a lot easier just to buy an off the shelf system, they come with tempering valves & all the bits & pieces...plus mains power if you want it...

Pedro -Dawn- · 08-03-2022, 21:30

Quote:

Originally Posted by zstine

the OP system may work but almost certainly more money and complexity than a standard off the shelf heater. He's got a separate heat exchanger, a circulation pump, a tank, and a thermostatic valve and then bits and bobs to connect it together. Yes, it will probably work, maybe not well(?), but for under $300 bucks you can get a tank with a heat exchanger inside and be done. No extra pumps or valves to fail or consume power. Why spend more and get less?

Hey two-rocks & Dooglas!

Problem is I am doing this refit in Brazil. There are no locally produced boiler systems under ~1000USD. But my main concern is the lack of local craftsmanship for marine applications. It is just a huge gamble to buy anything here. Also adding current logistics bottlenecks and increasing cost...

For any imports, we face major taxation issues down here. Take a look at this screenshot. Its just an example. A USD100 Whale Foot Pump delivered by Amazon would cost me USD249.39. There are no heaters available for delivery by Amazon. Ebay service is very iffy and a lot of people face significant fines when importing. The workaround this issue is to import parts under USD50, which are not taxed, or most likely will pass by customs without inspection.

As the title of the thread mentions, this is a VERY DIY system. I am building the tank from a 8" CPVC pipe which someone in a construction site close by gave me. All in I've spent so far:

Heat exchanger $55.14
Coolant reservoir $9.49
CPVC Boiler tank $0.00
Copper coil $26.68
Pressure Relief Valve $21.89
TOTAL so far $113.20

If it works, Hey! pretty nice. If not, is not like I am too deep in this project. But the comments to the thread certainly helps me a lot!
Cheers!
Pedro

Pedro -Dawn- · 08-03-2022, 21:39

Quote:

Originally Posted by captstu

I installed a "tempering" valve on the domestic output of the hot water heater - it blends cold water to maintain a hot, but not scalding, temperature as the hot water heater cools with use.

You could turn it down a bit to be just warmer and run a single line at a warm temperature - but I think you will miss cold tap water for drinking and cooking.

The tempering valve comes from Amazon:

https://smile.amazon.com/Thermostati...dDbGljaz10cnVl

Hi Capt Stuart,

I will certainly do that! It is my assumption, also, that for a 19L tank (my build), it could save me a lot of hot water by mixing at the source. So in my galley I will have 4 faucets... 1 salt, 1 fresh, 1 hot fresh and 1 filtered. Not the most elegant, I know..

The only thing I'd say about buying this stuff from Amazon is that there is some markup associated with it. I'd go straight to the source and buy at Aliexpress.

Cheers!
Pedro