Bypass valve for Buderus G115WS/3?

jesmed1

The Buderus G115WS/3 literature calls it a "low temperature" boiler, but in the fine print of the installation manual, it says that for systems containing large water volumes (>115 gal per MBTU), a bypass valve must be installed to redirect some of the hot supply water back into the return to maintain boiler water temps above 130 F.

I'm asking about this because I'm evaluating our options for when we need to replace our two oversized Weil-McLain WGO-5's. Sharp-eyed @EdTheHeaterMan saw in a pic I posted that our WGO-5's do not have the bypass valves required by Weil-McLain to keep temps above 140. And because this is an old 4-unit house with massive amounts of radiation and massive amounts of water in the pipes, the water rarely or never gets above 140. So these boilers have run for 25+ years with water almost always below Weil-McLain's spec minimum.

Despite that, the boilers are in surprisingly good shape, with no evidence of ill effects from the dreaded condensation that may or may not actually be happening.

So in evaluating options for new boilers when the time comes, I'm looking at what each mfr says about minimum water temps and whether a bypass is required. Weil-McLain, Burnham, and Buderus all require bypass valves in low-temperature applications like ours. The only suitable boiler I can find with no minimum water temp is the Biasi B10 (and maybe that's because I haven't found the right manual yet.)

Right now I'm leaning towards the Buderus G115WS/3, as that's a boiler our oil company is familiar with and likes, and it is advertised as being able to cope with low water return temperatures.

So my question is whether anyone has experience with the Buderus G115WS/3 as a cold-start boiler, and if you have any comments on the bypass valve requirement. I guess it's cheap insurance to install one anyway whether or not it's actually needed. Apparently our WGO-5's don't really care that our water temps are so low with no bypass. Wondering if the Buderus would be any different.

Big Ed_4

With a cold start the combustion gases will condense until the boiler reaches 120* , The system bypass does not have to be full size as the supply size , A ball valve is use to throttle or adjustment ... It would nice to have if needed

jesmed1

Big Ed_4 said:

With a cold start the combustion gases will condense until the boiler reaches 120* , The system bypass does not have to be full size as the supply size , A ball valve is use to throttle or adjustment ... It would nice to have if needed

OK, thank you. As you say, nice to have if needed, and it's a trivial cost to install when the boiler is put in. I'm just curious if anyone has seen bad effects from a bypass being omitted and boilers running too cold as a result.

EdTheHeaterMan

I have worked on boilers for over 40 years. I have seen Weil McLain boilers and other Pin type boilers where the pins near the top of the heat exchanger have rusted away to small pencil point spurs compared to the original 1/4" rounded off pins that were there when they were new. Your boiler(s) are so oversized that the flue gas temperature is hot enough to burn off that condensation when the water temperature reaches maybe 110° or 115° at the return. That is a unique situation for your boilers. The flue gas condensation happens when the flue gas temperature is low. The boiler water temperature helps keep that flue gas temperature low on some jobs. If you were to connect one boiler to both sides of the building, without a bypass, you may end up with a completely different set of circumstances that may result in the boiler rusting away as a result of the low stack temperature created by the larger system volume (2 radiator systems on one boiler).

I believe that was touched on in one of your other discussions. Someone said many water heaters operate at 120° maximum all the time and they don't experience Condensation problems. I beg to differ with that assumption because I remember one of the first atmospheric burner Gas Automatic water heaters I installed, Filled with cold water and turned on the burner... Then I heard water dripping on the burner. I though for sure that the tank had a small leak. Turns out it was condensation accumulating on the baffle in the "center flue" tank. Once the water temperature got past 95° the dripping stopped. So the design of that tank and burner is such that when the water is really cold, there is condensation... but when the water is warmer the condensation stops. But it is designed for 120° tank temperature.

Weil McLain wants 140°. Buderus wants 130° and other (non-condensing) boilers all have a similar issue. When the return water is consistently below a certain number. There is a chance of condensation. Not a guarantee of condensation.

Better safe than sorry.

jesmed1

EdTheHeaterMan said:

Someone said many water heaters operate at 120° maximum all the time and they don't experience Condensation problems. I beg to differ with that assumption because I remember one of the first atmospheric burner Gas Automatic water heaters I installed, Filled with cold water and turned on the burner... Then I heard water dripping on the burner. I though for sure that the tank had a small leak. Turns out it was condensation accumulating on the baffle in the "center flue" tank. Once the water temperature got past 95° the dripping stopped. So the design of that tank and burner is such that when the water is really cold, there is condensation... but when the water is warmer the condensation stops. But it is designed for 120° tank temperature.

Weil McLain wants 140°. Buderus wants 130° and other (non-condensing) boilers all have a similar issue. When the return water is consistently below a certain number. There is a chance of condensation. Not a guarantee of condensation.

Better safe than sorry.

Thank you @EdTheHeaterMan. Interesting story. I know natural gas combustion produces more water vapor in the flue gas than oil combustion. Does that mean gas heaters/boilers are more prone to condense at low temps than oil?

But as you say, better safe than sorry. If we were installing the Buderus, would we use a mixing valve like this with a preset temperature? Or just use a plain ball valve or gate valve and experiment with how much to leave it open?

https://www.supplyhouse.com/Caleffi-280166A-1-Female-NPT-ThermoProtec-Thermostatic-Mixing-Valve-140-Degrees-F-Tset

Here's a previous discussion where ball valve was used and seemed to work OK once set properly.

https://forum.heatinghelp.com/discussion/191875/boiler-bypass

One interesting feature of the Buderus is removable baffles that can be taken out to increase the flue gas temperature. I expect that means slightly lower efficiency as more heat goes up the flue, but that would presumably be another way, in addition to the bypass, to reduce the possbility of condensing.

EdTheHeaterMan

Thank you @EdTheHeaterMan. Interesting story. I know natural gas combustion produces more water vapor in the flue gas than oil combustion. Does that mean gas heaters/boilers are more prone to condense at low temps than oil?

YUP!

But as you say, better safe than sorry. If we were installing the Buderus, would we use a mixing valve like this with a preset temperature? Or just use a plain ball valve or gate valve and experiment with how much to leave it open?

Caleffi was not around here 40 years ago... so I did the gate valve if I wanted a full port valve or globe valve if it didn't matter. Ball valves are not the best for throttling but will work in a pinch.

One interesting feature of the Buderus is removable baffles that can be taken out to increase the flue gas temperature. I expect that means slightly lower efficiency as more heat goes up the flue, but that would presumably be another way, in addition to the bypass, to reduce the possbility of condensing.

Best practice is the bypass valve idea. No one wants to intentionally make a boiler less efficient to operate.

jesmed1

EdTheHeaterMan said:

Caleffi was not around here 40 years ago... so I did the gate valve if I wanted a full port valve or globe valve if it didn't matter. Ball valves are not the best for throttling but will work in a pinch.

Ok, thanks. I see the Caleffis come with different preset temps. Since Buderus wants minimum 130 degrees, it looks like this one would work:

https://www.supplyhouse.com/Caleffi-280165A-1-Female-NPT-ThermoProtec-Thermostatic-Mixing-Valve-130-Degrees-F-Tset

EdTheHeaterMan

Have we determined if you need 1" Piping for the near boiler piping or 1-1/4". I guess that will depend on what boiler goes first, and if you purchase a boiler to do only one side of the building (the one that breaks down) or If you go for one that will do the whole building. You know that one or both of the owners of the other side won't want to pay for the boiler if they still have a working boiler. Then after you get the proper size boiler for your side and put your own oil tank in to operate the new properly sized boiler, the other two will see that you are paying a lot less to heat your side. Then they will ask to get a lower fuel bill, but by that time you already have one new boiler and a perfectly good inefficient boiler on the other side. Then let them do the research and purchaseing for themselves. And don't tell them about the stuff you learned here. Let their plumber make the mistake and maybe install it wrong.

Am I being too pessimistic, or do I just know human nature?

jesmed1

LOL. Yes, you know human nature.

We do have 1-1/4 pipe at supply and return, so we probably would get the larger mixing valve. The 1-inch is what happened to come up on the supplyhouse link, so I just copied the link as an example.

But you're right. One boiler will go, and the two condo units heated by that boiler are supposed to pay for its replacement. The other two units won't want to abandon their still-working WGO-5. So a new boiler will go in for just the two units. Probably a WGO-2 or a Buderus G115WS/3. Hopefully with the correct bypass valve if I'm not here to bird-dog the installers.

The two 275-gal oil tanks are tied together, however, and will probably stay that way. All units split the oil cost 4 ways. So the other 2 units will get partial benefit from reduced oil use, which is fine. Once everyone realizes how much less oil they're burning, that will make the next boiler replacement a little more palatable.

Watch now, after all my research and planning (and your very helpful input for which I am grateful), these WGO-5's will last another 10 years, and I will have moved away! But I've written everything down for the next boiler installers to reference on heat loss, boiler size, water temps, etc. Hopefully someone reads it...

Meanwhile I keep hoping one of these dinosaurs croaks so we can replace it.

EdTheHeaterMan

I would split the tanks when the new boiler comes in. The installer can do that. Then rewrite the rule about the 4 way split. Since your side spent the $$$ for the more efficient boiler... Why should the other side get the benefit?

Just Sayin'

All 4 get the new boiler and all 4 get the benefit. only 2 buy the new boilerm then only 2 get the benefit. Fair is fair.

The other side can even go with a different oil company. Just make sure the oil fills are prominently marked

jesmed1

EdTheHeaterMan said:

I would split the tanks when the new boiler comes in. The installer can do that. Then rewrite the rule about the 4 way split. Since your side spent the $$$ for the more efficient boiler... Why should the other side get the benefit?

We could do that. OTOH, it might be the other side's boiler that goes first...fortunately, everyone in the building is nice and we all get along well.

Mad Dog_2

The Buderus/Bosch G 215 is designed and set up to better handle situations like this, but I forget how small they go.  Mad Dog 🐕 

jesmed1

Mad Dog_2 said:

The Buderus/Bosch G 215 is designed and set up to better handle situations like this, but I forget how small they go.  Mad Dog 🐕 

Unfortunately the G215 only goes down to 117MBTU/hr net, which is still too high. We want to be down around 70-80MBTU/hr. I guess it's not really a problem to install the bypass, but it would be nice to find a boiler that didn't have the low water temp concern.

I've read the Biasi B10 installation manual carefully, and it doesn't say anything about minimum water temps or bypass. The only thing it says is there must be positive water shutoff like a zone control valve to prevent gravity circulation after the boiler stops firing. I'm going to try to contact a Biasi dealer and confirm that it doesn't need a bypass.

EdTheHeaterMan

I don't believe that the Laws of Physics apply differently to Biasi. But maybe they have good lawyers and have found some loopholes in that Law.

jesmed1

EdTheHeaterMan said:

I don't believe that the Laws of Physics apply differently to Biasi. But maybe they have good lawyers and have found some loopholes in that Law.

I'll report back what they say. It is interesting that they don't want gravity circulation after shutdown. But at that point there are no more flue gases, so it can't be a condensation concern. Maybe they don't want the cast iron to cool too fast and develop thermal stresses.

EdTheHeaterMan

jesmed1 said:

EdTheHeaterMan said:

I don't believe that the Laws of Physics apply differently to Biasi. But maybe they have good lawyers and have found some loopholes in that Law.

I'll report back what they say. It is interesting that they don't want gravity circulation after shutdown. But at that point there are no more flue gases, so it can't be a condensation concern. Maybe they don't want the cast iron to cool too fast and develop thermal stresses.

Not the reason. Stop gravity flow in order to prevent overheating in the home. More for zone systems where gravity flow from one zone may find its way to other zones not calling for heat. Also if you were to have a single zone with Baseboard heat (or any other small water volume system) the gravity flow, after the thermostat is satisfied, the heated water's gravity flow may over heat a second floor section while the first floor loop stays at the thermostat setting. Or the gravity flow may only get to the beginning of the loop leaving the end of the loop cooler. Flow check valves will reduce that imbalance.

And I find it interesting that there are no piping diagrams at all in the "owners manual". I wonder if there is another manual for the installer?

jesmed1

EdTheHeaterMan said:

Not the reason. Stop gravity flow in order to prevent overheating in the home.

OK. Just weird that none of the other boiler installation instructions have that requirement for positive water shutoff after the boiler stops firing.

This is the only "manual" that I could find, and it does have wiring diagrams and a section (#5) titled "Piping" that seem to be written for installers. But there aren't any piping diagrams, just the Section 5 text about piping.

https://qhtinc.com/wp-content/uploads/2022/03/2022-B10-MANUAL.pdf

I've been in touch with a Biasi rep by email and am trading Q&A's with him now on this topic.

jesmed1

@EdTheHeaterMan You are right as usual! Even though the Biasi documentation says nothing about a bypass, this is the reply I got from their rep:

"We always recommend primary/secondary piping. But in a retro application with no primary/secondary piping, a by-pass will function similarly. Stack temp with the Biasi B10 series should be around 350º to avoid flue gases from condensing."

So any boiler we consider is going to need a bypass. Not a big deal, but it's good to know. I wonder how many installers know to do this, any how many know but ignore the instructions. I'm guessing the guys who installed our WGO-5's knew they were supposed to install a bypass but didn't for the sake of expediency.

HVACNUT

The Buderus G115 has a 1 inch return to throttle down the flow. They also claim you cannot shock their block.
I believe they now come with the Hydrostat 3250 Plus which has a circulator hold off function, and you can set a minimum water temperature for the circulator to energize.

EdTheHeaterMan

jesmed1 said:

@EdTheHeaterMan You are right as usual! Even though the Biasi documentation says nothing about a bypass, this is the reply I got from their rep:

"We always recommend primary/secondary piping. But in a retro application with no primary/secondary piping, a by-pass will function similarly. Stack temp with the Biasi B10 series should be around 350º to avoid flue gases from condensing."

So any boiler we consider is going to need a bypass. Not a big deal, but it's good to know. I wonder how many installers know to do this, any how many know but ignore the instructions. I'm guessing the guys who installed our WGO-5's knew they were supposed to install a bypass but didn't for the sake of expediency.

I Think I'm going to save this for future use. Did you see that @ethicalpaul, @STEVEusaPA, @WMno57 and @109A_5. I Try to tell you all to listen to me! LOL

jesmed1

HVACNUT said:

The Buderus G115 has a 1 inch return to throttle down the flow. They also claim you cannot shock their block.
I believe they now come with the Hydrostat 3250 Plus which has a circulator hold off function, and you can set a minimum water temperature for the circulator to energize.

Thank you; I didn't know about the Hydrostat 3250 and its holdoff function. That could actually be useful. A combination of that plus a bypass valve would be extra insurance.

WMno57

I always listen to Ed.
My 80 year old Weil McLain has no boiler protection. It condenses when I start it up in the fall. Warm start, so during most of the winter, no condensation. Last winter the batteries in the thermostat died while I was away for a week. Came home to a 40 degree house. Massive condensation recovering from that. That convinced me all boilers should have some type of boiler protection.

jesmed1

WMno57 said:

I always listen to Ed.
My 80 year old Weil McLane has no boiler protection. It condenses when I start it up in the fall. Warm start, so during most of the winter, no condensation. Last winter the batteries in the thermostat died while I was away for a week. Came home to a 40 degree house. Massive condensation recovering from that. That convinced me all boilers should have some type of boiler protection.

Interesting. Gas or oil fired? We have two oil fired Weil McLain WGO-5's that cold start and have survived 25+ years just fine with no bypass or any other type of condensation protection. Maybe we just got lucky, or maybe the guys who installed it knew from experience that, in our setup, those boilers would not condense, or that the condensate would burn off as the boiler heated up without causing problems in the long term.

WMno57

Gas, originally Oil. A Midco gas power burner was installed about 50 years ago. Warm start, and the Aquastat is independent of the Thermostat. After the thermostat is satisfied, the boiler continues to run until it hits 170. I think the power burners dry out the boilers better than atmospheric burners.
Not very efficient, but natural gas is cheap. BTU for BTU, the wholesale price of oil is 7 times the wholesale price of Gas. Just a few weeks ago Oil was 8 times the price of Gas.

Mad Dog_2

I love the old thread protector coupling and bushing on the gas line!  That boiler has been well cared for.  Waxed better than my cars 🚗!   Those Midco's run forever. Mad Dog 🐕 

jesmed1

WMno57 said:

BTU for BTU, the wholesale price of oil is 7 times the wholesale price of Gas. Just a few weeks ago Oil was 8 times the price of Gas.

Wow. You must live near a natural gas field. Here in the Boston area gas is about 30% cheaper than oil per BTU. I looked into converting, but the payback period was too long. Would be a different thing if we lived wherever you are.

WMno57

NW Indiana. 35 cents a therm for September 2023 . My bill says the 35 cents includes a 22 cent per therm interstate pipeline transportation cost. So gas cost is 13 cents a therm. Today's spot price for gas is $3.18 per mmbtu (ten therms). My utility must have bought gas futures contracts that are much lower than today's spot price.
Fixed cost for the gas meter/service is much higher than oil service.
Variable costs per BTU are much lower.
The 7 times figure is based on today's wholesale spot prices.
$3.18 mmbtu gas
$2.89 gallon heating oil
https://finviz.com/futures.ashx

jesmed1

Wow. Here the costs are about $2/therm (total with delivery) for gas and $3 for the same BTU's in heating oil.

EdTheHeaterMan

The real cost for gas and for oil and for electricity is the bottom line. Where my gas bill says PAY THIS AMOUNT is the number I divide the cubic feet used into. Natural gas charge, transmission charge, pipe line charge, meter charge and taxes are all part of what I pay.

That is the only way to compare the cost of fuel. BTU per dollar spent. Not the wholesale cost of the stuff. I can get waste oil for free and burn that stuff. But I need a special burner, equipment to pump the oil from the repair shop that changes oil, barrels to transfer. and all the time it takes to do all that stuff. BUT MY HEAT IS FREE!

NOT!

WMno57

Fixed costs and variable costs are both important to consider.
My point was my variable costs are very low. Going from a 50 percent efficient boiler to a 90 percent boiler will not reduce my bill by 40 percent. The fixed costs remain the same.