Bosch Mini Tank as an Expansion tank

seekingexp

New member
I got this idea from this thread, https://medium.com/@mylifewodoor/diy-high-altitude-hydronic-van-heating-3c68ef42dc47

I am putting together my hydronic diesel heating system. It will be an Espar fired furnace that heats a loop for floor heat, a fan blower, a heat exchanger for domestic water and another loop for heating exterior tanks. I really love the idea of using the Bosch mini tank as an expansion, and as a buffer. It will also allow me to use electricity to heat the coolant. Unfortunately I don not think the author ever did this so I would love to hear peoples opinions on this idea.
 

Aqua Puttana

Poly - Thread Finder
The system should never be under any real pressure. Assuming that the tank is vented (fill cap vent?), that expansion tank should work fine.

FWIW. I added an expansion tank to a walk-in van engine cooling system. I just used a windshield washer tank from a scrapped vehicle. It worked fine.

:2cents: vic
 

owner

Well-known member
I did something similar. I used a Duoetto. But my Espar is the stock coolant heater one, not separate like that link. I pipe the house water out to the engine bay and use a 60 plate FPHE there. So the house water is heated by engine and/or Espar heat, and brought back to the Duoetto at the sink and shower. I had thought about a radiator in the fresh circuit for rear air heating, but we don't really need that down here. The dash heater is plenty here. The fresh loop can also cycle through a tap into the underbody freshwater tank if freezing was ever going to be an issue. The Duoetto is a 10l SS tank with 12V/240V elements. It has a relief valve vented under the floor.
 
So I am clear, the expansion tank like those 2.5 gallon electric water heaters would have coolant in it ? I can't tell if the the original author intended to use it for coolant or h20
 

seekingexp

New member
Yes it will be used to heat coolant which will also act as both a buffer and a way to use electricity. I am starting to think I will also need a small expansion tank also.
 

Midwestdrifter

Engineer In Residence
You need a tank which is open to the atmosphere. It doesn't need to be full flow, it can just be a single hose. However make sure you have provisions to bleed air out of the system, or the pump can vapor lock and there will be no flow. An expansion tank with room for 750ml of expansion will probably do the trick, but you might need a bit more if you have air trapped in the water heater.

Instead of an electric water heater, there are also electric external block heaters for cars/trucks. These are smaller, and come in various wattages. I doubt you need a 4 gallon buffer, especially with all that floor heating length. Just make sure your cut in/out temps are far enough apart to prevent short cycling.

My plan is to use one of these block heaters in series with my coolant hydronic loop. This loop passes through my expansion tank and water heater coolant loop. This allows me to use the hot water as a thermal reservoir to increase cycle length. On a second loop which connects to the main loop with tees on each side of the water heater is my anti-freeze loop. This heats my external water lines/tanks, and the shower floor. This loop has its own pump. Using a custom made controller I can keep the second loop under freezing, and cycle the pump on the second loop, and the main heater/pump as needed to keep everything above freezing.
 

seekingexp

New member
You need a tank which is open to the atmosphere. It doesn't need to be full flow, it can just be a single hose. However make sure you have provisions to bleed air out of the system, or the pump can vapor lock and there will be no flow. An expansion tank with room for 750ml of expansion will probably do the trick, but you might need a bit more if you have air trapped in the water heater.

Instead of an electric water heater, there are also electric external block heaters for cars/trucks. These are smaller, and come in various wattages. I doubt you need a 4 gallon buffer, especially with all that floor heating length. Just make sure your cut in/out temps are far enough apart to prevent short cycling.

My plan is to use one of these block heaters in series with my coolant hydronic loop. This loop passes through my expansion tank and water heater coolant loop. This allows me to use the hot water as a thermal reservoir to increase cycle length. On a second loop which connects to the main loop with tees on each side of the water heater is my anti-freeze loop. This heats my external water lines/tanks, and the shower floor. This loop has its own pump. Using a custom made controller I can keep the second loop under freezing, and cycle the pump on the second loop, and the main heater/pump as needed to keep everything above freezing.
I am curious what kind of controller you will be using. I was just going to use some inkbird thermostats to open valves and maybe power up a second pump.
 

Midwestdrifter

Engineer In Residence
I am curious what kind of controller you will be using. I was just going to use some inkbird thermostats to open valves and maybe power up a second pump.
Probably a custom unit, arduino with relay board. There are industrial units which are pretty flexible.
 

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