Buffer Tank / Thermal Storage needed/recommended for new Pellet/Log Boiler?

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Expat_Latvia

New Member
Oct 4, 2021
7
Latvia
I'm having a new boiler furnace installed in my house (Domusa Dual Therm 35KW). It can use both pellets and logs. I plan to use both. Installer says not to use a Thermal Storage or Buffer Tank. He says the size we'd need won't fit thru the door of the house into the furnace room.

I read this old thread:

And...I'm a bit confused. Okay many people say thermal storage isn't needed with a wood pellet boiler but IS needed with a log boiler due to safety/overheating issues if the power goes out with a load of logs burning. For sure my current boiler has overheated if the primary pump is unplugged so that's a known issue, blows the relief valve.

We will use this boiler to heat our domestic hot water. So that tank is supposed to be 300 liters. Calculations I saw say a 35KW system should have at least 700 liters of buffer for overheating protection (70 gallons per 10,000 BTU heating power or so). So some people say that the domestic hot water tank can be used as a sort of thermal storage. Should I buy a much larger domestic hot water tank then? Currently we have 150 liters which is not enough for our family so 300 liters seems like enough but I'm willing to go bigger if needed.

House is not zoned, does not have any temperature gauges in the rooms to communicate with the boiler. It's all quite old school. So there won't be any "calls" made to the boiler, just from the control panel and domestic hot water tank.

As far as Domusa goes they say any of the 5 following installation methods are acceptable:

17.6 Managing BT and BT-DUO buffer tanks
Parameter P.08 is used to set the type of hydraulic installation that has been used for the BT or BT-DUO buffer tank. This parameter depends on the instllation and must e set by the installer once the buffer tank has been assembled. The factory default value is 0, management function of BT buffer tanks is disabled. The elctronic control of the DualTherm boiler is able to manage the operation of 4 different types of installation.

Function Disabled
Installation with Sanit DHW tank after BT tank and control by temperature sensor
Installation with Sanit DHS tank before BT tank and control by temperature sensor
installation with Sanit DHW tank after BT tank and control by thermostat
Installation with Sanit DHW tank before BT tank and control by thermostat

Ultimately I just want a better heating system for my house and family. I don't really trust my installer (part time sub-contractor to the company I bought from) and I'm looking for other opinions before we go ahead with the install.
 

brenndatomu

Minister of Fire
Aug 21, 2013
7,517
NE Ohio
I don't recall the name right now, but there is someone here in the states that sells a storage system that easily comes apart to be taken in/out of tight spaces...maybe one of the other boiler guys will come along here soon that remembers the name...
 
35 kW sounds like a good size boiler.
To my knowledge all cordwood gasification boilers are installed with plenty of thermal storage in europe.
I would recommend minimum 500 gal for 35 kW.
Domusa is an advanced brand.
They have great combustion technology.
But with a gasification boiler, once the fire is going there is no way back as full trottle forwar: so definetely thermal storage
 

hobbyheater

Minister of Fire
I don't recall the name right now, but there is someone here in the states that sells a storage system that easily comes apart to be taken in/out of tight spaces...maybe one of the other boiler guys will come along here soon that remembers the name...
 
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maple1

Minister of Fire
Sep 15, 2011
10,963
Nova Scotia
IMO, storage is a must when burning cord wood. Not so much pellets. And it's not for over heat protection as mentioned above. It is to allow you to batch burn - burn wide open until the fuel is gone. Then you make another fire when the house needs heat again. How much storage to use IMO is also not directly related to the size of the boiler. It is more directly related to how far you want to go between making fires. Yes it should as minimum hold all the heat from a full fire box of wood, but usually if storage is cold and has anywhere near a desirable size, it will. I have around 700 gallons in my total system. Would love 1000 but space was an issue. And there are other means of overheat protection.
 
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Expat_Latvia

New Member
Oct 4, 2021
7
Latvia
Maybe there was a miscommunication due to language issues. The head service manager said of course we need a buffer tank and the service plan includes one. They put a 400 liter (100 gallon) thermal buffer tank into the plan which seems very small. We have another discussion, at least, before I give the go ahead for the installation.
 

peakbagger

Minister of Fire
Jul 11, 2008
7,689
Northern NH
I f you look on the website they had a fire at their shop and they currently are not making tanks. Too bad as I have one and its nice kit for getting a big tank through a small door. I installed mine complete solo.
 

Expat_Latvia

New Member
Oct 4, 2021
7
Latvia
I f you look on the website they had a fire at their shop and they currently are not making tanks. Too bad as I have one and its nice kit for getting a big tank through a small door. I installed mine complete solo.
Looks good. I could put this under the stairs in my basement and hold a lot of water. But I don't think they do business in Europe so I'll have to look for something else available in Europe that'll fit into my house thru the doors...