Westinghouse 80k BTUh boiler setup for best efficiency

[Bunny Laroche]

Hello, this forum has been so helpful in the past that I thought I would post another request asking for advise about how best to set-up my Westinghouse 80k BTUh boiler.

The gas company's technician inspected the system and turned on the gas at our house a couple of weeks ago. The system has since performed better than we expected, but then again the weather has been much milder here in Northern Minnesota than usual.

So the only changes to the boiler's factory default setup that my girlfriend (she installed the boiler and radiators and pipes to connect everything) made were to enable the boiler's "step modulation" feature, she changed the duration the boiler will wait before satisfying the next call for heat to 20 minutes (an effort to reduce the boiler from cycling on and off too frequently), and she also turned the maximum boiler supply heat down to 160F from 180F, saying that as the winter wears on we will likely need to adjust that temperature.

I wonder what the general opinions about these changes might be, as well as any advice for any further changes/modification that might help set up a more efficient system?

BTW, although we installed an 80k BTUh boiler, the heat analysis for our home suggested that we should only require about 35-40k BTUh to keep things toasty and warm on the coldest days of the year.

 

[Leon82]

your going to want to play with the odr reset curve.

I think that boiler can limit the max firing rate which will extend the burn times

 

[Sponsor]

 

[Jac04]

What specific Westinghouse boiler do you have? Is it a condensing boiler? I'll base my comments on the assumption that it is a modulating condensing boiler. There are 2 things you want to do to maximize efficiency: 1) Get the return temperature (which should track with supply temperature) as low as possible to take advantage of the condensing efficiency, and 2) Limit the firing rate as low as possible.

Ideally, the boiler would come on once at the beginning of the heating season and run continuously in a throttled-down state, 'riding' the outdoor reset curve to keep the supply temperature at exactly the right temperature to keep the house at a constant temperature. This will yield maximum efficiency. In reality, this typically doesn't happen.

Now, you haven't mentioned any specifics about the boiler or what you are doing with the heated water (baseboards, radiant heating, hydo-air?) If you give us more info, some of the more experienced board members can give you some guidance on how to set the boiler. Do you actually have your supply temp set at 160F? If so, that seems really high unless there is something unusual about the heating system. What are your burn times? Short burn times will give you a quick indication of whether or not the supply temperature is too high.

 

[Bunny Laroche]

Hello fellas,

Thanks so much for the replies.

What specific Westinghouse boiler do you have? Is it a condensing boiler?

The precise boiler model is: a Westinghouse WBRU**80W Universal Fire Tube Boiler, Wall Mount. It is definitely a condensing boiler, or at least I hope so has been purging lots of water out of the neutralizer my girlfriend installed on the wall.

Do you actually have your supply temp set at 160F?

Yes that is correct, except my girlfriend turned the supply temperature setting to 155F yesterday as means for less boiler cycling. I guess the burn times have been short, as you ask. The boiler comes on frequently but does not remain on for long periods of time. The temperature here in Northern Minnesota hit a low of about 5F, but during the day for the past couple the temp has hovered around 20F. So the temp outside is feeling more normal for this time of year.

Although the boiler's fan speed is still at the factory default setting of 00, my girlfriend has mentioned that perhaps the boiler might benefit from that setting being lowered.

you haven't mentioned any specifics about the boiler or what you are doing with the heated water

The secondary loop is piped through steel radiators split into upstairs-downstairs zones. The radiators really do radiate a nice amount of heat so far, so we are hopeful we went with the right choice for heat emitters.

My girlfriend is an electrician so she asks her colleagues most of the questions regarding how best to set up the boiler, but I am not sure how much useful information she receives in reply. So that is why I am also asking for some help on here about some setting changes we might be able to make to better set this boiler up for the long haul through the colder winter month bearing down upon us. I appreciate the advice and suggestions.

 

[Leon82]

You want the bottom of the odr curve to be around 100 to start for radiators. The boiler will adjust the temp of the water for the temp outside.

For example

Outside temp 50. Water temp 100
Outside temp 0. Water temp 155

 

[Leon82]

So now your radiators put out enought heat for the thermostat to turn off quickly. As you tweak the odr curve they will put heat out slowly and take longer for he thermostat to satisfy

 

[Bunny Laroche]

As you tweak the odr curve

So would reducing the boiler's fan speed also help to tweak the "odr curve," in addition to reducing the boiler's maximum supply temperature, to where it will be more efficient for our particular situation?

There are two 3-speed water pumps (circulators I think) installed in the primary loop: one feeding the supply and the other drawing back the return, which we just turned from their MIDdle to LO setting last night in an effort to help better moderate (slow) heat output.

 

[Jac04]

What are your actual burn times with 155F supply temp? Are we talking like 1-2 minutes? If so, that means the supply temperature is much too high for whatever outdoor temperature the 1-2 min burn times are occurring at.

By "fan speed" do you mean firing rate? The firing rate will not change the ODR curve. ODR = Out Door Reset, which is referred to as Outdoor Temperature Mode in your manual. Do you have the outdoor temperature sensor installed and are you actually using the Outdoor Temperature Mode?

Anyhow, you want to use the lowest supply temperature possible to meet your heating needs. You can just keep lowering the supply temperature until the boiler runs constantly and the thermostat requirement is never quite met, then bump it up about 5 degrees. You will need to do this at different outdoor temperatures to get a feel for how to set the ODR curve. If you are not going to use the ODR, then you will need to find the supply temperature that works for your actual outdoor Design conditions.

 

[Bunny Laroche]

Do you have the outdoor temperature sensor installed and are you actually using the Outdoor Temperature Mode?

Yes the ODR module is installed on the north side of our house located under the raised porch. I remember when my GF installed this unit she was then able to measure a voltage on the boiler's OS terminal leads on the terminal block, indicating I believe that it should be working.

By "fan speed" do you mean firing rate? The firing rate will not change the ODR curve.

There is a system setting in the "installation mode" labelled FAN SPEED. The factory default is "00," but can be swung to "+/-30." When the boiler turns on the FAN speed can be observed to slowly rise in speed until it gets to ~4500. My GF has read that lowering the water pump speed might help to reduce the return temperature, and I think she wonders if lowering the boiler's FAN speed could have similar beneficial results. Perhaps the info we need about this is in the Westinghouse manual, but we have found so far that some settings such as FAN SPEED are just not clearly explained enough for a couple of women like ourelves.

There is a LOw and HIgh fire mode in addition to NORmal fire mode, changed by two switch on the boiler's control board. The gas technician had my GF change these switches in order to run the boiler on both LOw and HIgh fire so he could measure the combustion on both as part of his inspection process. But my GF has not mentioned changing the "fire" to LOw or HIgh from NORmal as a means to better tweak the ODR curve.

Thanks a lot for the wonderfully quick replies that are instilling confidence in us, allowing us to proceed to get the most out of this new boiler for our circumstance.

 

[Dana]

The fan speed will not lower the return water temperature, but may reduce the maximum burner output.

Even though he's several hours drive away, you might contact Morgan Audetat (posts here as BadgerBoilerMN ), a pro who recently installed the HTP version of that boiler in his own place, and is undoubtedly tweaking-in the ODR curve on his as the winter temperatures arrive.

 

[NY_Rob]

There's really no reason to tweak the burner fan speed (12:FH and 13:FL) because there is a actual function available to limit the boiler's heating capacity (18:cb) to prevent hitting high limit and not being able to modulate down quick enough once the water makes a complete loop around the space heating circuit. You may also experiment with step modulation (37:CM) to stop the boiler from climbing to max fire rate too quickly on short calls for heat. You can use use 'limit heating capacity' and 'step modulation' together to extend burn times.

In my system, on DD (15F) my heatloss is just under 30K BTU's, so I used the 'limit heating capacity' and set it to 50% so the boiler now is in essence a 40K BTU boiler and doesn't throw a full 80K BTU's at my space heating loops which helps prevent short cycling. 'Step modulation' helps on my shortest zone that heats up quickly.

 

[Leon82]

So would reducing the boiler's fan speed also help to tweak the "odr curve," in addition to reducing the boiler's maximum supply temperature, to where it will be more efficient for our particular situation?

There are two 3-speed water pumps (circulators I think) installed in the primary loop: one feeding the supply and the other drawing back the return, which we just turned from their MIDdle to LO setting last night in an effort to help better moderate (slow) heat output.

There are parameters for the odr temp curve. I dont know exactly what they are but the book should say. You shouldn't have to adjust fan speed

 

[NY_Rob]

All the above tweaks including adjusting the Outdoor Reset curve come back to knowing your heatloss figures, without knowing it- you're just guessing. You also have to have the figures on your zones- particularly your shortest zones in order to see how low your SWT can go before short cycling on your shortest zone. You may want to go down to 110F SWT (100F AWT)... but if you have 40' of fin tube on your short zone that only puts out maybe 5,400 BTU's so you'll short cycle on a boiler than can only fire down to 8K BTU's and need to raise the SWT another 10-15F.
Of course shoulder seasons present another set of challenges too.

 

[Leon82]

The fan speed adjustment is there for rare occasions that may pop up.

The odr curve will be a little trial and error. It is the only way to lower the supply temp without making the max temp too low

 

[NY_Rob]

If found Excel to be extremely useful in ODR calculation experiments.
If you know your heatloss, and your total fin tube length- you can calculate the AWT (SWT-10F) you need on DD to keep up with heatloss.
You then take in to account your shortest zone BTU output, and always want to be condensing (RWT below 130F)... so fire up Excel- put your low and high outdoor temps in... let autofill populate the cells between low and high, right next to the outdoor temp columns start a column with your high SWT, end it with your low SWT and let autofill populate the cells between the two... rinse and repeat with differing SWT's high and low values and see what you come up with. I needed 128F SWT at 15F (DD) and didn't want to go below 115F AWT (to prevent short cycling) on my shortest zone when we still need heat... so I ran numbers in Excel and am currently using the blue highlighted column in the included worksheet.
All in all it's a compromise... but armed with your system particulars you at leas have a starting point.

 

[Bunny Laroche]

Thanks for the wonderful suggestions in your replies. I was away for the past couple of weeks but my girlfriend continued to tweak our boiler settings and it appears as though we are getting closer to an ideal setup as she described how the boiler runs for much longer periods than not.

there is a actual function available to limit the boiler's heating capacity (18:cb)

We overlooked this setting completely, so we really appreciated reading your setting description and suggestion. We too, went ahead and

set the option on our boiler to 50% so the boiler now is in essence a 40K BTU boiler

, since the heat loss calculation for our whole house is ~35,000BTUh.

My GF does not like working with spreadsheets, but she has been diligent while I was away to keep a list of temperatures stickied to the front of the boiler so we can keep track of what CH temperature satisfies our heating demands for any given outdoor temperature. Unfortunately we are victims once more this year to a slow start to winter, as the temperature has been unseasonably mild. It has barely dipped below 32. But so far it appears as though for outdoor temperatures between40-32F, the boiler's CH needs to be set to 110F in order to just barely keep the upstairs thermostat happy when it is set to 70F.

So as the outdoor temperature will hopefully begin to drop soon we will continue to increase the boiler's CH temperature so it just keeps the upstairs thermostat barely satisfied, and we should soon enough have our own unique heating curve to keep our cozy little abode efficiently comfortable.

We do wonder though, since we are so surprised how low we have had to set the CH temperature to keep the boiler running *almost* continuously, is there a valid concern at all by setting the boiler's CH temperature too low, even if it still manages to satisfy the thermostat? Is there any chance lower temperatures in the pipes can create an incubation-like environment that is warm enough to promote but not kill bacterial growth?

 

[NY_Rob]

The space heating loop is a closed system- devoid of O2 after several days of initial firing- so no chance of bacterial growth.
If you're getting your domestic hot water from an indirect tank- the loop that circulates through the boiler is sealed too, so no chance of contamination there either.

If you're at all concerned about Legionella, you can keep your indirect tank temp setpoint at 140f to kill bacterial growth and use a tempering valve to bring it's domestic output water down to the mid 120F range if desired. I keep my DHW setpoint at 135F because we have no small children in the house that could be scalded by that hot water. Homeowners have been using mid 120F DHW setpoints for years without problems- mainly because the DHW system in a normal household has no dead-ends and is not stagnant for any length of time.