Series versus parallel plumbing for boiler - question(s)

[MrEd]

Hi all.

Tarm is here and I am reading all I can getting ready to dig into the install over the summer.

Everything is subject to change of course, but so far I am leaning towards the tarm in a new shed about 40 feet from the house. I'll run underground insulated pex of some sort to the house, and then hook pipes to my existing oil boiler in the cellar.

My simple plan was basically that the hot output from the tarm would plumb into the cold/return of the oil boiler, and the hot output of the oil boiler would connect to the cold/supply of the wood - I didn't realize that there were at least several other options available to me. Reading 'nofossils' very informative website, I gather that would be considered a 'parallel' installation instead of a 'series' install.

His choice, according to his site was series, and the big negative about my choice is that no matter which boiler I am running, it is being forced to heat the other, therefore is loosing heat. In some respects, I get that, but in my case where the Tarm is outside, and I am not planning on using anti-freeze, would that 'negative', in fact be a positive if I went away for a couple weeks in the winter and didn't burn wood? Seems I would use more oil(when I was away), but the benefit would be that the tarm would always stay warm.

What other considerations should I be thinking about as I decide between series/parallel, primary/secondary, suppl/return...?

 

[WoodNotOil]

My tarm is in parallel with my oil boiler. It is piped hot to cold like you plan to do with a pump on the return of the tarm. The pump only circulates heat to the oil boiler when the boiler needs it. All heat for the house is drawn from oil boiler. I set the the low on the oil boiler low enough so that as long as the tarm is up to temp it won't need to fire at all. The oil furnace does not supply the tarm with heat. The aquastat on the heat out pipe of the tarm knows when the tarm is under temp and does not circulate. It would be very costly to heat the 54 gallons in the tarm with an oil boiler! Instead the oil boiler keeps itself hot and supplies heat to the house even when the tarm is stone cold. Anti freeze in the closed system lines will be required to not damage the tarm and pipes. I don't think there is anyway around that. I am very happy with my parallel system and have not noticed efficiency issues.

 

[MrEd]

I am not sure how I understand how your setup doesn't circulate water from the oil boiler to the wood boiler if you only have just the one pump?

I agree it would take an extra bunch of oil to have the oil boiler heat the tarm, but in my case, for the one or two weeks per year when I am not home 24/7, that is a good thing (i.e. having the oil burner keep the wood boiler in my outside, insulated, shed warm when it is not running).

 

[WoodNotOil]

I have one pump that is dedicated to circulation between the boilers. I have other pumps for the zones. With the aquastat in the exiting pipe from the tarm, the pump will not run when the tarm is under temp. If you theoretically wanted the the oil boiler to keep the tarm warm, you would have to have additional controls and sensors on the pump.

 

[MrEd]

I am probably just being dense here, and I don't mean to belabor the point, but if the output of your tarm is piped to the input of the oil boiler, and the output of you oil boiler is piped to input of your tarm, what I am picturing is that as the tarm runs, it pushes hot water into your oil boiler. And if the oil burner is running, it is pushing hot water out into the tarm...but perhaps you have it piped differently than I understand. Any chances of posting a schematic of you piping?

 

[WoodNotOil]

Here is the schematic of my existing system. The aquastat only circulates water when the tarm temperature is within the set range. When the tarm is stone cold it does not circulate. The aquastat is not like a traditional thermostat. It has a range of about 20* that it will circulate water in. I hope that helps clarify.

 

[Nofossil]

Hi all.

Reading 'nofossils' very informative website, I gather that would be considered a 'parallel' installation instead of a 'series' install.

His choice, according to his site was series, and the big negative about my choice is that no matter which boiler I am running, it is being forced to heat the other, therefore is loosing heat. In some respects, I get that, but in my case where the Tarm is outside, and I am not planning on using anti-freeze, would that 'negative', in fact be a positive if I went away for a couple weeks in the winter and didn't burn wood? Seems I would use more oil(when I was away), but the benefit would be that the tarm would always stay warm.

What other considerations should I be thinking about as I decide between series/parallel, primary/secondary, suppl/return...?

Must be some other nofossil. I'm a big advocate of parallel for the simpler cases, with the possibility of primary/secondary for more complex situations.

What you show is an interesting variant. Looks like Tarm water would circulate through the oil boiler, but not vice versa. Any reason not to hook them up purely in parallel to a common supply and common return? If you're worried about freezing, you could run the Tarm circ for a few minutes every once in a while when temps are cold. You'd have to have an open zone valve to provide a loop under those conditions, but that would solve the freezing issue without the waste of heating an inactive boiler.

 

[MrEd]

Are you sure you didn't just edit your website(kidding)??? I thought for sure I read on your site that you chose 'series'...maybe I've just been reading too much lately and got things confused.

Anyway, so now (and maybe always!), you site says parallel - which is also what I want to do. How can I setup my system to run parallel, but also (maybe with a manual ball valve or two), plumb it so that when I go away for a week in the winter, I can get the oil boiler to circulate hot water thru the tarm - even thought it costs more and is inefficient).

Suggestions?

 

[Nofossil]

Are you sure you didn't just edit your website(kidding)??? I thought for sure I read on your site that you chose 'series'...maybe I've just been reading too much lately and got things confused.

Anyway, so now (and maybe always!), you site says parallel - which is also what I want to do. How can I setup my system to run parallel, but also (maybe with a manual ball valve or two), plumb it so that when I go away for a week in the winter, I can get the oil boiler to circulate hot water thru the tarm - even thought it costs more and is inefficient).

Suggestions?

Simplest suggestion: install a relay that can open a zone valve on one heat zone in the house. Install a thermostat on the Tarm set for some really low temp like 40 degrees. When that thermostat calls for heat, wire it to open the zone valve and turn on the Tarm circulator. That should do it. It will circulate warmed water through the Tarm, even if the oil boiler is off at that moment. It will cool the house a bit, but only enough to keep the Tarm at 40 degrees.

 

[solarguy]

If your existing oil fired boiler is old & has been kept hot its whole life you may want to consider a series piping arrangement. Although it's not the most efficient way of hooking up a system you'll need to decide if you want to gambel on if she'll start leaking when she cools off.

 

[webbie]

Both installations have their ups and downs. In a care where the wood boiler has a small water capacity, parallel might help add to the water storage and make it go into overheat less often. But larger capacity (water) boilers probably give more flexibility in this case. Also, the use of continuous circulation (mix valve) makes the house part of the storage, which makes the whole point somewhat moot (in this case, both boilers are kept hot in either installation).

I'm probably behind the times, but a main idea is to have some circulation going on at all times so the wood boiler does not overheat or turn down too far. In the case of series, this could be one of the house circs along with the mix valve. In the case of parallel, this is an added circ between the two boilers.