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

[Expat_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:

Does a Pellet Boiler Need Storage?

I'm thinking it wouldn't, but could someone verify? Also nothing special for a chimney - right out the side of the house. Might save install cost anyway.

www.hearth.com

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]

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...

 

[PassionForFire&Water]

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

 

[PassionForFire&Water]

this is a link to the manual.
(broken link removed)

It looks like thermal storage is REQUIRED, as it is not optional like some of their other options.

Probably lost in translation from Spannish to English

 

[hobbyheater]

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...

American Solartechnics, LLC.

Last Updated: March 6th, 2024 December 2nd, 2022 - Between the fire we had this summer and our other business endeavors keeping us busy, we have been considering stepping back from the Heat Bank...

www.americansolartechnics.com

 

[maple1]

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.

 

[Expat_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]

American Solartechnics, LLC.

Last Updated: March 6th, 2024 December 2nd, 2022 - Between the fire we had this summer and our other business endeavors keeping us busy, we have been considering stepping back from the Heat Bank...

www.americansolartechnics.com

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]

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...

 

[Expat_Latvia]

Final Post:
There were communication issues with the company and installation contractor. I don't speak the native language of this country. In the end, of course we got a thermal buffer tank (accumulation tank) which is mandatory with the Domusa system. 400 liters, which is about 100 gallons. It's the biggest one they could get into our house they say.

We had to complain a lot to get proper service and get the installation done right, but in the end we're happy. The house has never been so warm and the accumulation tank is a big deal. I come from the USA and electric heat pumps with forced air central cooling/heating so I didn't realize how critical the thermal buffer tank/accumulation tank is to making these boiler systems work well.

Total cost was about $13,000 including installation, delivery etc. ~6K for the furnace, then the domestic hot water tank (300 liters) and accumulation tank, various pumps and all the rest. Sold the old furnace for $850 which was surprising to me because I didn't think too much of it.

The Domusa DualTherm 35KW furnace eats a lot of fuel but puts out a lot of heat. The price of wood pellets is very high right now so I'm trying to burn as much firewood as possible but sometimes I don't have time to move wood from the wood shed into the furnace room so I end up burning pellets. It's good to have that option, but it's burning money (literally). Last year a ton of pellets was ~$150 and right now they're $400+. If I only burned pellets my house could easily use 1.5 to 2 tons a month which, again, is why I'm trying to burn as much firewood as possible (much cheaper, puts out a lot of heat).

Conclusion: I'm happy with the Domusa DualTherm system and it keeps my house very comfortable even in 10 below. The really cold weather (-20C or colder) will come early next year. House is something like 3700 square feet of heated living space for your information.