Hydronic heating experiment

[etischer]

I hate the furnace in our trailer, it's so loud, I wake up every time it turns on. These heaters haven't changed much since the 70's. I pulled mine out, and designed a new heating system that uses hot water from the water heater to heat the inside of our trailer. I Still have finishing touches to do, but so far it seems to be working well. It should be putting out about 2kw of heat. I ran an air duct to the bathroom, one at the foot of the bed, and two ducts at the galley floor. It's much quieter, we can run the fan at 20% and still have plenty of air flow, and not worry about anything catching fire. We now have heat throughout the trailer instead of one spot. We also benefit from having instant hot water at the sink. We can also run the heater off electric or gas since our water heater is both.

 

[profdant139]

Fantastic! (No pun intended.) Would you consider writing up what you have done? I know that is a big task, but it makes it easier for other folks (like me) to steal (I mean copy) your ideas.

The big issues, for me, are first, how to hook up to the water heater -- I see the photo, but is there a sensor valve? Second, the hydronic heat exchanger -- which one did you use?

Thanks!!

 

[etischer]

I still have a few improvements to make before posting a how to.

Here are the heater parts I used.

https://www.jegs.com/i/JEGS/555/70607/10002/-1

https://www.jegs.com/i/JEGS/555/70608/10002/-1

https://www.jegs.com/i/JEGS/555/70610/10002/-1

The heater has (3) 2.5" holes. I made a new faceplate with (4) 2" holes, but if you can find a 2.5" duct kit, that would make life much easier. There were also heaters on eBay with (4) 2" ports, but I was afraid they might be too cheap and rattle, and have exaggerated specs. Jegs has quite a few heater options, that seem to be a bit better quality.

I did some testing this morning, and was only getting about 11 deg/hour rise, which seems really slow. I had the water heater preheated, and for the hour of testing, the water heater drew 1300 w/hr. The gas burner never fired up.

As far as improvements: The cold side of the water heater has a non-return check valve that's spring loaded, this restricts the circulation pump by about 50%. I need to move this so it's not restricting recirc, but still prevents hot water from entering the cold supply line. I think I should be able to extract a bit more heating power with better circulation.

Another option is to have both the original furnace, and heater core heater installed underneath. The installation manual for the Suburban furnace shows 0" clearance requirement on the bottom. With my heater core installed, I have about an inch to spare, and the space under the furnace is kinda useless. I imagine the original furnace is more efficient use of battery (BTUs/AH).

 

[etischer]

I moved the non-return valve on the cold side of the water heater so it doesn't restrict my recirc pump, and it made a big improvement. I'm now getting almost twice the heat, 20 deg F per hour!

I was also able to install the original furnace, but hoping after a few camping trips, we can determine it's unnecessary.

 

[etischer]

I ended up sticking a Siemens "LOGO!" PLC on top to some timing tasks. I have the PLC programmed to run the pump for 20 seconds so the heater is hot before the fan turns on. The fan runs slowly for 20 seconds until the ducts are warm, then runs at full speed (set by the dial). If the heater restarts within 5 mintues, the delays are bypassed and the fan starts up right away.

If anyone is interested in the PLC, it's super easy to program, you don't even need a computer. Here are the notes I used to program:

notes

I wrapped the ducts with insulation, and I think this project is done.

 

[profdant139]

I am in awe. I think this project is beyond my abilities, but I sure wish I could harness the heat of my water heater for space heating. It is so much more efficient and quiet.

 

[etischer]

Added final touches. Replaced the thermostat, built up the floor in the kitchen cabinet to hide the ducts, and added a switch to select Furnace/Heater. Also upgraded my battery monitor.

 

[profdant139]

Brilliant! If this significantly reduces noise and electricity consumption, you may be able to start a business selling a kit of components and detailed installation instructions.

 

[etischer]

Brilliant! If this significantly reduces noise and electricity consumption, you may be able to start a business selling a kit of components and detailed installation instructions.

Well it is quiet, but it's not very efficient. A portable electric heater would be 100% efficient. The gas furnace is fire-to-air, verses fire-to-water, water-to-air. The furnace heat exchanger is much hotter than the 135 deg F heater core, so for the same volume of air blown, the furnace puts out more heat; and it also doesn't have a water pump running.

The heater core system is definitely quiet. It's also nice to have vents blowing on the floor, across the foot of the bed, and in the bathroom. It's also nice having instant hot water. Variable blower speed option is also nice, and no worry of something burning up. It's also so small, it fits under the existing furnace. It's also Gas + Electric if your water heater is G+E. I'm excited to start testing it out, next camping trip in 3 weeks.

We rented an RV in Switzerland and it used a Truma Combi (combination water heater and ducted furnace); this is basically what I was trying to mimic for around $400. I think the Combi is the ultimate solution, but it is $2-3k.


Here are some pics of the heating system in our Swiss RV.

Water heater and furnace in one unit, and it's smaller than our water heater.

Really cool that the heating ducts surround the perimeter of the bed.