Can't Figure Out How A Piggybacked Pellet Boiler Would Work With An Oil Boiler

[velvetfoot]

Can anyone clue me in on this?

I've read the Harmon Hydroflex60 install manual, done some searches here but I can't get how it would work if the two boilers were connected.
How does the pellet boiler start, and the oil boiler not start, when both boilers are cold? If the Harmon was in manual mode keeping the circulating water at something more than the aquastat setting of the oi unitl, but that could cause an excess heat issue. If the Harmon was in auto mode, a call for heat would both boilers , no? That would be undesireable. Do I have to have dual thermostats for each zone, with the oil set lower than the pellet? Where would that leave the indirect water heater (Boilermate) then? There'd be no chance of putting in another aquastat in that.

I'd like to go with this boiler, but I have to figure out how it'll work with the existing one first.

Thanks for any help.

 

[Chris Hoskin]

the two boiler set-up you describe is very common. Your installing contractor/dealer will know how to make it work no problem.

 

[MrEd]

Without a doubt, there are controls that can handle this for you. My low-tech solution with my oil burner and my Tarm wood boiler, is to simply turn off the power to the oil burner. Its the easiest thing to do if you don't need the automatic fallback to oil when the alternative boiler/heater is not running.

SInce I work at home, I don't worry about the house going cold, and if I am not going to be here for an extended period of time in the very cold weather, I turn on the oil boiler before I leave.

 

[stoveguy13]

auto / manual mode refer to the igniton not to how it runs the the simplest way to get what you want would be to plumb the hydro in to the return of you oil unit and and lower the water temp on your boiler to 150 and set the hydro at 160 so it will send hotter watter into the oil burner then it is looking for and stoping your oil from turning on depening on you plumbing and location of the units some would need to look at the system and see exactly what needs to be done

 

[velvetfoot]

Thanks. My dealer didn't think it would be a problem either, though I believe he did mention different settings on the two aquastats. He mentioned nothing about additional controls, and there's nothing in the manual about it either. I'm still interested in exactly how it would work.

 

[stoveguy13]

sent you pm

 

[velvetfoot]

Thanks stoveguy. I replied before you posted. As I understand it, running it on manual mode would mean that when there's no demand for heat, the pellet feed rate will go down to 1, still kicking out the heat ultimately to the dump zone, which doesn't seem like that great an idea. On automatic, my understanding is that the unit shuts down totally, using the electric ignitor to get the fire going when there's another demand for heat. At the point in time before it fires, the water temperature could be below the minimum aquatat setting for both boilers.

 

[velvetfoot]

stoveguy, thanks very much for your help!

 

[stoveguy13]

no problem