Bosch Combi boiler's

[purediesel]

About 3 years ago we poured a 6" floor in our barn and it was always meant to have heated floors. We installed 2 zones of 1/2" pex on 12" centers with 9 loops on our shop side and 5 loops on our storage side, all loops are 300' long. This was all installed on 25psi xps foam board over 15mil Class A vapor barrier. So fast forward to today and I have an opportunity to get a Bosch Greenstar 151 combi boiler for a pretty darn good deal and I was just wondering if anyone has any experience with this boiler or any Bosch's similar boilers. While I wasn't planning on having DHW service it may be nice since we will have a full bathroom in the barn. Thanks for any input.

 

[Mr onetwo]

I have had the bad luck to deal with one of these boilers about 5 years ago.So many problems with it.Finally had to retain another contractor to get the thing to run right.Awful non-intuitive controls and internal parts replacement was a nightmare.I have no info on what model it was.IMHO I wouldn't touch a Bosch boiler with your 10 foot pole let alone mine.Viessmann Vitodens all day every day.

 

[kj_mustang]

I have a Bosch Greenstar ZBR-28-3 heat only boiler running propane. Runs my floor heat and I use an indirect hot water tank for DHW. Running fine for about 5-1/2 years now. Zero issues.

 

[Jackfre]

Most of the wall hung mod cons out today are pretty good from a “product” standpoint. I do agree with the Veissmann comment above. The thing with the wall Hung’s is that they MUST be properly installed and set up. Your margin for error shrinks considerable when you move a2way from the large cast iron block of the traditional boiler.

 

[yeldogt]

About 3 years ago we poured a 6" floor in our barn and it was always meant to have heated floors. We installed 2 zones of 1/2" pex on 12" centers with 9 loops on our shop side and 5 loops on our storage side, all loops are 300' long. This was all installed on 25psi xps foam board over 15mil Class A vapor barrier. So fast forward to today and I have an opportunity to get a Bosch Greenstar 151 combi boiler for a pretty darn good deal and I was just wondering if anyone has any experience with this boiler or any Bosch's similar boilers. While I wasn't planning on having DHW service it may be nice since we will have a full bathroom in the barn. Thanks for any input.

What's the heat load on the building ? That boiler has a minimum input of over 30k btu ... 36K btu -- how big is the building?

My new house in PA with over 4k of space has a 60k Viessmann -- indirect for hot water . I have a studio that is around 1600 with 15k of heat.

What is a good deal ..... ? NG or Propane?

 

[purediesel]

Thanks for the input fellas. The barn is a 50x80x16 and we will hopefully be adding a 30ft addition to make it a 50x110. As for the boiler, the one that I am looking at getting is a floor standing model of the Greenstar 151 and will be running LP. Only difference between wall mount and floor standing is the addition of a low loss header. This will come in handy with my current setup of zones. Even using this as a single zone boiler I would need the low loss header since the 151 internal pump is only good for 4gpm and the shop has 9 loops of 1/2" tubing. .6gpm x 9 loops= 5.4gpm As for a good deal, I think at over 50% off would classify a good deal to me. One of the best things about this deal is that the boiler is brand new in the box, I forgot to add that in the original post. Since were getting into building specs I'm sure someone will be asking about wall and ceiling details. The ceiling is roughly an R44 from blown in fiberglass and the walls have R7 1.5" xps between the girts and then spray foamed the gaps to make it air tight. Over the 1.5" xps is an unfaced R19 fiberglass batt that is covered with 6mil poly vapor barrier, also the entire building is wrapped with house wrap.

 

[yeldogt]

My boiler has a 10/1 turn down so I can get somewhere in the 6-8k BTU range ......the problem with combination boilers is they have to be sized for heating the domestic water.. Your boiler will just have to fire on and off.

Radiant systems benefit from a LLH because it maintains correct flow to each system component. Boiler circulator is designed to give the boiler the proper internal flow so as to remove the heat it is producing (the primary loop). The secondary loop can now be fitted with a circulator to provide what's need to the radiation loop -- pex is restrictive and the heads are too great to use direct flow with only one pump (no primary/secondary) and have the boiler get it's 4gpm flow. Flow on the secondary side is based on heat transfer needs --- that's why the new smart pumps work so well .... proper flow not max flow. Needed flow is based on BTU transfer needs

A single smart pump -- pumping away from a spirovent setup can do multi manifolds. Here is my last system as it was being set up .... 4 manifolds over 30 loops w/ 2 remote manifolds about 40 feet away. The secondary is 1.25 copper. This set up has three circulators. Primary with this boiler is external -- secondary off of LLH. Circulator to Indirect tank for domestic hot water. The two heating loops are using smart pumps (one fixed) and the Indirect has a simple dumb 3 speed. The smart pumps use very little energy .. so even though one of them is not really set up to be smart it's only using 14w vs about 80w .... running 24/7 in the heating season that adds up. Plus it allowed me to play around a bit.

Many people think they can connect up a wall boiler and using one pump flow water out of the boiler and into a PEX manifold ... this only works in small systems. As you add pex loops the head grows and the flow through the boiler drops .. this increases temps through the boiler. Higher temps usually have the boiler going on and off -- or even hitting high limit ... at some point the flow we be too low for the boiler to fire. This is why some here have problems when they copy other systems. That boiler loop is very important

 

[Mr onetwo]

I absolutely agree on the use of a low loss header in a larger system.Solves a lot of problems.I am using a Resideo (Honeywell Braukman) Hydrosep in my own house.Really nice product. https://www.supplyhouse.com/Resideo-HYDROSEP-103-U-1-1-4-Union-Hydraulic-Separator

 

[purediesel]

From my research it sure sounds like the llh is a must on most radiant heating systems that we use on this forum. From the cost of them I am glad that this boiler already comes with one factory installed. I have now moved onto pump sizing and what a ton of information to take in. One thing I am sure of is that I want to run a vfd pump to make the best out of the setup and to be able to run more zones in the future.

 

[yeldogt]

From my research it sure sounds like the llh is a must on most radiant heating systems that we use on this forum. From the cost of them I am glad that this boiler already comes with one factory installed. I have now moved onto pump sizing and what a ton of information to take in. One thing I am sure of is that I want to run a vfd pump to make the best out of the setup and to be able to run more zones in the future.

One alpha II is all you need .... the same as in my picture.

LLH is always the best way to go with the low mass condensing boilers. The heat exchangers are restrictive and need/require a specific flow for the BTU extraction (primary). This never matches the radiation requirements (secondary)

big cast boilers and big radiators -- the type used in hot water heat 100+ years ago has almost no resistance. That's why the early coal systems did not even have pumps. Same with small systems where guys use a tank water heater ... the tank has no resistance.

 

[fitter30]

14 loops x300' 147k btus. 35 btu per ft how is the system piped

 

[purediesel]

Good outlook and it does put this boiler to max output at 35 btu per foot. Hopefully with all the insulation that is installed and the measures taken for air sealing the building will be more along the lines of 20 btu's per foot.

 

[Mr onetwo]

Just to let you know, this boiler does not contain or include a low loss header.Also, it has an aluminum heat exchanger...be very careful of the ph of your feed water.I wouldn't touch an AL heat exchanger boiler with a 10 ft pole.

 

[purediesel]

You are correct, that one does not included a llh. That is not the one that I am getting. Mine will be a floor unit that does included a llh. Please elaborate on the problems that you have seen with the aluminum exchangers.

 

[Mr onetwo]

They are very sensitive to water quality especially with well water.There are ph requirements as well as iron/mineral limits.You have to clean and treat with Fernox or equal.Any indication of bad water and Bosch will not warrantee the heat exchanger.As you can tell I don't like Bosch boilers in general and would never use one.Viessmann, with they're stainless steel/titanium heat exchanger is far superior IMHO.Been putting them in for many years and have had 1, I said 1 service call in all that time.I had to replace a main board due to a lightning strike...not the boilers fault.Just my opinion and experience.

 

[purediesel]

They are very sensitive to water quality especially with well water.There are ph requirements as well as iron/mineral limits.You have to clean and treat with Fernox or equal.Any indication of bad water and Bosch will not warrantee the heat exchanger.As you can tell I don't like Bosch boilers in general and would never use one.Viessmann, with they're stainless steel/titanium heat exchanger is far superior IMHO.Been putting them in for many years and have had 1, I said 1 service call in all that time.I had to replace a main board due to a lightning strike...not the boilers fault.Just my opinion and experience.

I have an RO system up an running that I can use to fill the system. TDS is down to 4 but the ph will have to be looked at closer when its time to fill the system. Last time I checked my ph was 7.8 so Ill have to look closer at the Bosch requirements.