Finally got propane backup installed

[Nofossil]

My backup heat has been fuel oil, but I've been facing two problems: the oil boiler is almost 25 years old and has not improved with age, and I last bought fuel oil in 2007 and I'm almost out.

I bought a Takagi TK-50 jr instant-on propane hot water heater a couple years ago, and it's finally installed. I have it plumbed in parallel with the wood, oil, and storage (see diagram below). It's capable of providing hot water at 182 degrees, and is rated for space heating. It's appears to modulate both the combustion and the flow through the HX to hit its target outlet temp.

I'll have to do some real testing. In a brief inaugural firing, it heated 72 degree water to 180 degrees at about 2gpm. We'll have to see what it does with more typical inlet temps. The HX provides a LOT of flow restriction, so I expect that it will be flow limited. Updated plumbing diagram:

 

[Fred61]

Will it handle return water temperatures over 100 degrees or is that likely to mess it up? Years ago my brother had photo processing equipment that required a constant flow of hot water so he installed electric instant hot water units to increase the temperature of the water coming from his 100 gallon propane fired heater that couldn't handle the flow. They had about a 30 day lifespan.

 

[Nofossil]

It modulates the flame, so it should deal OK with higher inlet temperatures. Much more testing to be done, though. I'm using a Grundfos UPS 26-99, which should give me a decent flow rate.

 

[BoilerMan]

Got some pics? Is it PVC vented or a Z-Vent? I know I can look this stuff up, but it's better coming from you NoFo.

TS

 

[STIHLY DAN]

Wow, thats quite the system. How do you have the controls on it? Will the TK 50 modulate low enough for 100* return? Many of these modulating units can only go down to 30%.

 

[Nofossil]

I'll work on a picture today. It's Z-Vent, and it's on the wall in my boiler room.

How do I control it? That's a really long story. Grab a cup of coffee and pull up a chair....

On second thought, short version: My installation evolved over the last 7 or 8 years with a lot of involvement from folks on this forum. The story of my journey is here. I built my own control system which came to be called the NFCS, and which has since become the Vesta system.

Another Hearth member has the Vesta system and is posting his progress installing it in another thread.

At present I control the propane boiler with the Vesta, though I'll eventually wire it up to the house thermostats and DHW aquastat as an independent failsafe system.

 

[Nofossil]

Here's a picture - boy, does the iPhone take a crappy picture in low light.

With the Grundfos UPS 26-99 that I'm using, I should get about 4gpm which translates to about a 55 degree rise through the propane heater, which translates to about 100k BTU/hr. I don't expect that I'll get return temps low enough to achieve a 55 degree rise without exceeding the 182 degree maximum, so I won't get 100k BTU/hr in actual use.