Temperature difference on pellete boiler(HydroFlex) and oil boiler

If you really are circulating between the two boilers at all times, I'd have to guess that the thermometers don't agree, unless the hot from the Hydroflex is going out to the heating system and the return water is coming to the oil boiler, which would be a peculiar way to connect things.

As with clocks, the person who has one knows what time or temperature it is, and the person with two or more just knows that they never agree ;-) - If you can find a third, trusted thermometer and check both systems with it, you might gain some insight. It could also be worth insulating the pipes between the boilers, if they are not - a hot pipe will bleed a lot of heat, even without fins attached.

Flow makes perfect sense - hopefully the insulation will make a significant difference.

jervine10 said:

Hello everyone!

This is my first post. I've been reading through a lot of the topics here and have learned a lot! I have a harman HydroFlex 60 and absolutely love it. I didn't do the plumbing myself so I have more of a general knowledge of its workings. I believe it's plumbed in series. There's a pump that circulates water between the two boilers at all times.

I'm hoping to get a little bit of help to optimize the system. I have the feed rate at 4, and the min and max temps at 160/180. When the water reaches 180 in the pellete boiler, my oil boiler's temp gauge can run anywhere between 150-160 (usually closer to 150). Does that sound normal? Is there anyway I can bring that temperature up in the oil boiler without firing it? If I want to keep it up I can set the temp of the water in the oil boiler to 160+ but then it fires fairly often; once or twice an hour for a few minutes at a time.

Thanks for any help! Let me know if I need to explain more.

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There's a boiler forum that probably will give you all your answers, but it seems to me that the pellet boiler is cycling water from 160 to 180, which it then sends over to your oil boiler. As long as the temp doesn't drift below 150, the oil burner won't fire. Seems to be right, though I'm not sure if the oil burner differential should only be 10 degree. I've always seen 20 minimum, but I'm no expert.

jervine10 said:

Thanks everyone for the answers. Sorry, I wasnt aware this was the wrong forum, rookie mistake =)

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Hi Jervine10,

Velvetfoot sent me a private message, looking for me to comment on this thread. Please see my other posts on the HF60 in the boiler room.

This does NOT sound like a series install. I'm guessing you are circulating between the two boilers with 3/4" pipe and the house is circulating only through your oil boiler. The pellet boiler, fed with 3/4" pipe, can not keep up with the house load. I would definitely insulate your pipes between the two boilers.

Per one of my last posts in the Boiler Room, you should try using MANUAL Mode (with a dump zone connected) and your oil boiler will always be siting at the 180 Degree point, when nothing is running in the house. MANUAL Mode rocks when your HF60 is a little undersized for the job.

VT_Bubba

jervine10 said:

Thanks Bubba! I've read through that entire forum topic several times and have switched to manual mode... Although I don't have a dump zone connected, so I'll probably be back to auto before I go to bed. The install you described is exactly what I have, so apparently I was wrong about the series install. You mentioned 3/4" pipe is not enough to meet the demand of my house, can I redo the piping between the boilers and bump that up?

I'm quite surprised that it can't keep up with my home though. It's only about 1100 sq ft, and I rarely run more than one zone at a time...

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Jervine10,

Yes, you can re-plumb, but don't be so quick to change anything. I call all thermometers "Liars", because you can have 3 or more, and none of them agree !

Get your "Dump Zone" hooked-up to make sure "Manual Mode" has a place to dump excess heat, so you do NOT over heat the boiler and shut-down when in Manual Mode.

- Make sure you really have the Temperature Delta you think you have. If needed, go buy a digital Liar for another opinion.
- Wait for a warm day and turn-off all zones (t-Stats) and let the two boilers circulate with out any heating load. Do the temperatures begin to converge ?
- Then turn on a heating load and observe the temps in the boilers and the pipes. Is the house and oil loop significantly colder than the pellet loop ?

You can also increase the flow rate on the pellet loop, compared to the house\oil-boiler loop. I have variable speed circulators and run my Pellet Circ on Speed2, but the house circulators run on speed-1. Flow rates matter.. .If you think about flow and heat transfer, you will quickly figure-out what is happening.

However, you may find that a simple dump zone hook-up and manual mode is good enough for you.

I hope I gave you some ideas.... Please share what you learn with the forum !

VT_Bubba