Bunch of condensing boiler questions

lkhelp

Hello,
I've read many threads but still confused about many aspects of condensing boilers. Really looking for help here! Long story short, bought house and the tank and boiler decided to leak within the first week. Got several quotes for new heating system and ended up getting a Lochinvar Knight 110,000 BTU mod/con boiler with indirect 40 gallon tank (Heat Flo). While I understand that the modulating part of the boiler is already saving me money (I'm on propane and the old boiler was 164,000 BTU cast iron unit), I am very confused about how the system should be setup to utilize the benefits of condensation. Everywhere I'm reading that the return water should be 100-130 F range for the condensation to occur and the delta T should be 20 F. When my boiler is running even on one zone - it's typically showing delta T of only 2 degrees and the return and supply temps are in 150s or 160s. Does this mean the condensation doesn't occur? There's also a third temperature the display is showing - flue temperature and it's usually in 120s, but I think this might be in the pipe that vents to outside?
When the system was installed they said that for baseboard fins to open up they need to be running at 180ish and that's what he set the temperatures to be, but then for me to get 120-130 F on return water it sounds that it would be impossible to achieve. I guess the question is - if I lower the temps to the point where condensation can occur - would that gain in boiler efficiency outweigh the lost efficiency of baseboard fins? Would it also take much longer to heat up the house?
Sorry if this doesn't make sense, I think I have a quite a mess in my head from a week of reading online resources and talking to installers. Hopefully, folks here can help me straighten everything out.

Few details about the house: about 2,400 sq ft, three zones (typically, only one or two at most would be used at the same time), we are in Massachusetts. Attaching a photo of display on a "typical" boiler run and photo of plumbing (I think they've installed some primary/secondary piping here, but I am not clear on details at all).

Thank you very much in advance!

fenkel

The reason your contractor is using 180 water is: you do not have the correct feet of baseboards to run it lower..
1 ft of Baseboard @180 degrees supply temp. produces <= 580 btus per ft.
1 ft of baseboard @160 degree supply temp produces <= 450 btus per ft.
1 ft of baseboard @140 degress supply temp produces <=330 btus per ft.
When a heatloss calculation is performed,each room has a designed heatloss.. each room will be different...
Example..living room needs 5800 btus to heat the room on design day..
Youll need 10 feet of baseboards at 180 degrees supply ,
12.5 ft at 160 degree supply and aprox  16ft at 140 degree supply temp..
If you dont have the correct length of baseboards, you will not get a zone to heat correctly.. the end of the zone will be cold.. therfore youll need warmer supply temp to heat the zone..
Was a heatloss calculation performed?
Do you have an outdoor reset installed? This might help on days when its not that cold outside and will lower you temps down to be in the condensing range...
Does  the home heat nicely?
Id be more concerned with short cycling at this time... this will prematurely wear out your boiler...

psb75

Sometimes mod/con boilers are installed in settings where they can't do what they do best. If you don't have the right amount of radiation and if the house is leaky, your boiler won't be able to condense, unless you are willing to be cold. It is true that the return water temperature needs to be something UNDER 130F in order to condense. That's just the way water IS.

hot_rod

Know too, that a small % of the heatings season will you be at design condition. So even if 160 or higher is required for design, there will be days where low SWT and return will allow condensing. Get the outdoor reset function dialed in
You can wait and observe, or run the numbers starting with a room by room load calc and fin tube assessment

lkhelp

@fenkel Thank you, this is very helpful!

fenkel said:

The reason your contractor is using 180 water is: you do not have the correct feet of baseboards to run it lower

Not sure I understand this part. I measured the baseboard lengths and it came to about 68 feet for zone 1, 48 feet for zone 2, and 38 feet for zone 3. Last one also has 2 toe kicks.

fenkel said:

Was a heatloss calculation performed?

It was not. Basically, installer asked the square footage of the house and ballparked the max BTU from there. My understanding, that this approach would be frowned upon for older systems, but for the modulating systems - does it matter? The boiler can run at 10% capacity and I've seen it doing that. The fact that the zones need different temperatures is what I don't understand - the boiler will only output whatever temperature was programmed, right? I can't set one temp for one zone and another temp for another zone or can I?

fenkel said:

Do you have an outdoor reset installed? This might help on days when its not that cold outside and will lower you temps down to be in the condensing range...
Does  the home heat nicely?
Id be more concerned with short cycling at this time... this will prematurely wear out your boiler...

I believe it did come with the outdoor reset, but how would I verify that? It hasn't been super cold - 20s and 30s and 40s and I have not seen the return temperature under 150F when it's trying to heat one zone. It does briefly dip under 130F when the system is just starting or when it's also trying to replenish the water tank, but that does not last. Then it goes back to 150s and 160s or so for both return and supply with delta T of 1-2 degrees.

lkhelp

Youngplumber said:

Are all of your zones baseboard heat? I assume they are. 

Your extremely tight delta t  is probably based (like stated above) your heating needs.

If you change radiation type you could maybe get condensing like you want, but that's probably not called for. 

Heating systems are just that, systems. One hand washes the other.

I have to add this is my lightly experienced opionion. 

Thank you, I agree with your points. I understand that if I had radiant heating floors it would be a whole different story, but I am sort of shocked that it sounds like that it's impossible to get condensing going on baseboard heat? If that was that case it sounds like it's insane misuse of the condensing technology that is being installed left and right with existing baseboards.

EBEBRATT-Ed

@lkhelp

To further explain.
It looks like your contractor did a nice job from what the pictures show.

Baseboard systems can be run with low temperature water (in the condensing range) but that requires a large amount of baseboard. as baseboard puts out less BTUs at lower water temp

The contractor replaced the boiler and kept the existing system which is the normal thing to do on a boiler replacement.

As is you will probably get some condensation in the spring and fall when you can heat the house with low temp water. During the winter it will not condense when the outdoor temp is low.

This is provided the controls are set up properly.

You could add more baseboard if you have room. Is it worthwhile? maybe not

To figure this out would require a heat loss calculation of the house and a survey of the baseboard

lkhelp

psb75 said:

Sometimes mod/con boilers are installed in settings where they can't do what they do best. If you don't have the right amount of radiation and if the house is leaky, your boiler won't be able to condense, unless you are willing to be cold. It is true that the return water temperature needs to be something UNDER 130F in order to condense. That's just the way water IS.

Thank you! I have 68, 48, and 38 feet of baseboards in each zone, house is not super leaky... I mean I don't feel drafts and the insulation was just done before sale at least in zone 1.

Big Ed_4

You are right , condensing boilers were designed for low temperature radiation , Radiators and radiant heat are low temperature radiation . Baseboard is high temperature .

lkhelp

hot_rod said:

Know too, that a small % of the heatings season will you be at design condition. So even if 160 or higher is required for design, there will be days where low SWT and return will allow condensing. Get the outdoor reset function dialed in
You can wait and observe, or run the numbers starting with a room by room load calc and fin tube assessment

Thank you! It's been in 20s-30s-40s and I only see return temps under 130 when the system just starts firing up. It then quickly reduces delta T and keeps running at 10%-30% firing power until the zone is heated, but the vast majority of that time delta T is 1-2 degrees and return temps are 150-160... When you say "get outdoor reset function dialed in" - what do you mean?

Zman

You should be able to scroll through the settings and determine if the boiler is reading outdoor temp.
Your boiler circ is capable of variable speed and should be able to manage the boiler delta T to virtually any temp you like. The boiler is also capable of sensing and managing system temp.
My guess is that your installer did not enable/install everything they could have.
If you are comfortable powering down the boiler and taking a picture of the control wiring, we can probably get to the bottom of this.

lkhelp

EBEBRATT-Ed said:

Baseboard systems can be run with low temperature water (in the condensing range) but that requires a large amount of baseboard. as baseboard puts out less BTUs at lower water temp

Thank you! I'm assuming this means it will also take longer to heat up the house? The way that we use the heat is by setting it to comfortable temperatures when we are in that heating zone. We have Nest thermostats in all three (but with disabled learning feature) and basically dial them to 68-70 when we're in the zone and then turn it to 50-60 when we're not.
I guess the real question is - would the increase in efficiency through condensation be higher than decrease of efficiency of baseboards radiating not at high temperatures?

EBEBRATT-Ed said:

As is you will probably get some condensation in the spring and fall when you can heat the house with low temp water. During the winter it will not condense when the outdoor temp is low.

How low is low? Are we talking won't condense when it's 10s F outside or 30-40F?

EBEBRATT-Ed said:

This is provided the controls are set up properly.

And that is my main question really - at this point I have no idea how he setup the boiler other than it's supposed to be at 180ish to "open up the baseboard fins". How do I ensure the boiler's software is set to the optimal parameters?...

EBEBRATT-Ed said:

To figure this out would require a heat loss calculation of the house and a survey of the baseboard

When you say survey of the baseboard - what do you mean? Just lengths or also condition/dust/dirt/something else?
Again, thank you very much!

lkhelp

Big Ed_4 said:

You are right , condensing boilers were designed for low temperature radiation , Radiators and radiant heat are low temperature radiation . Baseboard is high temperature .

Got it, thank you. For some reason in my head baseboards were always lower temperature than radiators, but I guess that's because they're covered!

lkhelp

@Zman - thank you!

Zman said:

You should be able to scroll through the settings and determine if the boiler is reading outdoor temp.

It definitely reads outdoor temperature, it can be seen as 34F on the first photo. The question is I guess whether it takes that reading into account under current settings.

Zman said:

Your boiler circ is capable of variable speed and should be able to manage the boiler delta T to virtually any temp you like. The boiler is also capable of sensing and managing system temp.

Yes, I believe one of the selling points of Lochinvar Knight I read in the brochure was the variable speed. Great point about managing any delta T, I didn't think about this. Does this mean that it should be smart enough to slow down the circulator inside of boiler to reduce the speed with which the water flows through the system and thus return temps would be lower? But wait, there are separate pumps on each zone - won't they control the speed of water through the zone? I'm confused.

Zman said:

My guess is that your installer did not enable/install everything they could have.
If you are comfortable powering down the boiler and taking a picture of the control wiring, we can probably get to the bottom of this.

When you say control wiring do you mean inside the box on the wall that has power lines from pumps and water tank going to? It says Taco SR503 3 zone switching relay.

fenkel

To determine if you have odr.. look on a north facing outside wall..the box should be out of the sun light and on north facing exterior wall... the odr might have lochinvar on it...
If you have the ability...do a heatloss yourself...go to slant fin.com and try a room.. just need a tape measure...
Its fairly straightforward.. the heatloss from slantfin uses 180 for supply temp..
The results should help you understand why you might need 180 supply temp for heating..
Also. From the posted pictures, all zones use the same  supply temp to heat each zone...
You orginal system was probably designed to use 180 supply temps..

Zman

You are piped primary/secondary. The boiler flow rate can and will be different than the system flow rate. Yes, the boiler circ will turn way down to optimize the boiler delta T. This may trip up the system temp so Lochinvar recommends a system sensor.

If you turn off the boiler power, open the from cover, open the control box and take a picture of the wiring, that would help a lot.

Jamie Hall

Just a few points here.

First, a properly designed and installed zoned system can have different temperatures in different zones, if it uses zone pumps. It's a matter of installing a recirculation line through a mixing valve. The mixing valve mixes return water (cooler) with boiler water to get the proper temperature. The valve may be fixed, temperature sensitive, or controlled by a thermostat -- such as an outdoor reset.

Second, that big setback in the zones you aren't using is going to require fully hot -- 180 -- water from the boiler, pretty much no matter what the relationship between heat loss and radiation is. It probably isn't saving you anything, and may be costing you.

Without a zone by zone heat loss calculation and comparison with the zone radiation capacity, there is no way -- other than trial and error -- to determine what temperatures are needed to heat the zone. As I say, with the large setbacks you are using, you need the most it can provide anyway, whatever, to do the recovery.

Your delta Ts are very low. The tradeoff is between flow rate and delta T, and you may be much better off with lower flow rates.

Zman

Ideally you would have a wide delta at the boiler and lower delta at the zones.
I am sure you will be able to experiment with different settings on the outdoor reset curve.
Right now, you need to figure out why that boiler pump is not modulating and which sensors are wired.

Zman

I believe you will be able to condense on warm and shoulder season days. Even when you are running on the non-condensing mode, the fact that your boiler fully modulates and turns down 10-1 will make it far more efficient than a conventional boiler.

lkhelp

@Zman thank you!

Zman said:

I believe you will be able to condense on warm and shoulder season days. Even when you are running on the non-condensing mode, the fact that your boiler fully modulates and turns down 10-1 will make it far more efficient than a conventional boiler.

Yes, fully agree - the fact that I saw it running on 10%-30% firing power should save me money compared to older unit.
When you say warm/shoulder - what outdoor temps do you mean? 50s? 60s?

Zman said:

I am sure you will be able to experiment with different settings on the outdoor reset curve.

Haven't found those settings yet. I see that the zones are set at 180 and water at 120. Strange that boiler has settings for 3 zones but I think it runs as if it's all a single zone because it always only has a 1 symbol no matter how many zones are running. I'm not super comfortable taking the panel off yet, I have a tech coming for some other work and will take a photo when they're here next week.

lkhelp

@Jamie Hall thank you!

Jamie Hall said:

As I say, with the large setbacks you are using, you need the most it can provide anyway, whatever, to do the recovery.

Your delta Ts are very low. The tradeoff is between flow rate and delta T, and you may be much better off with lower flow rates.

When you say "large setbacks" that I'm using - what do you mean?
On the second part - how would I lower the flow rates?

Jamie Hall

lkhelp said:

@Jamie Hall thank you!

Jamie Hall said:

As I say, with the large setbacks you are using, you need the most it can provide anyway, whatever, to do the recovery.

Your delta Ts are very low. The tradeoff is between flow rate and delta T, and you may be much better off with lower flow rates.

When you say "large setbacks" that I'm using - what do you mean?
On the second part - how would I lower the flow rates?

You mentioned somewhere up there that you were turning unused space zones down to 50 or so, as I recall. That's really too low -- note my earlier caution about condensation (which would, in the long run, cost you a lot more in repairs than you'd ever save in fuel, by the way).

On the flow -- if the zone pumps are variable speed, try a lower speed. Otherwise, balancing valves.

lkhelp

Jamie Hall said:

You mentioned somewhere up there that you were turning unused space zones down to 50 or so, as I recall. That's really too low -- note my earlier caution about condensation (which would, in the long run, cost you a lot more in repairs than you'd ever save in fuel, by the way).

On the flow -- if the zone pumps are variable speed, try a lower speed. Otherwise, balancing valves.

Sorry, so do you suggest not lowering temperature in unused zones and keep them always warm? I set it at 50 but I don't think it actually hasn't gotten to that temperature, so far it stays in lower 60s overnight and then when we wake up - we crank them up to 68-70. Repairs that you mention - they would be due to what? Thank you for your answers, really appreciate!

Looks like circulators are not variable speed: Taco 007e-2fe.

fenkel

If the installer is coming over ask him if the boiler has a anti freeze program...
On some boilers this will keep the temp inside the boiler hotter ( because the internal pump will run when there is no call from any zone and outdoor temp is below the freezing set point)therefore,you will have very close deltas at the boiler...

HomerJSmith

Where does the condensate come from?

Condensate forms when the temperature and pressure is such that vapour turns to a liquid, the dew point. Are we talking about, Hydrocarbon dew point? How much water vapour is in a cubic foot of gas? Or are we talking about the vapour in a cubic foot of combustion air? I have been told that natural gas is run thru driers to remove water vapour.

We are all told that in a conventional boiler the return water must be above 130 deg or condensation of the acidic flue gases will harm the boiler and exhaust sys. I have personal experience of the damage that a mini fin-tube boiler experienced with continual operation with return water at 120 deg.

A Mod-Com boiler passed the flue gases thru a part of the HX that the return water enters, cooling the flue gases below the dew point and condensation occurs and transferring that heat energy to the incoming return water. (Pre-heating the return water)

What is the economic value of flue gas condensation? I think the economic value of a Mod-Com lies in the modulating feature with ODR and that far out-weighs the value of flue gas condensation.

As previously posted by others, Mod-Con boilers are not a perfect match to fin-tube baseboard. To get the economic value of modulating temperatures in a baseboard sys, one need an abundant amount of baseboard to compensate for the lower temperature of the supply water or you will be cold.

Your choice is to add more heat emitters or , with ODR, adjust the boiler's central heating curve to optimize your needs.

Jamie Hall

If you don't use those spaces daily, turning them down to 60 shouldn't cause any problems -- and will save. Daily? I'd not turn them down more than 5 degrees from your usual temperature.

The repairs I mention -- thought, I might add -- considerable learning the hard way on several properties -- are due to condensation. As the humid air in the part of the house you are occupying gets into the colder spaces -- and it will -- the relative humidity goes up, and if it gets cold enough (for instance if you are running relative humidity and 70 in the warm part, condensation will occur on anything colder than 55 in the cool part) that moisture will condense. There are two areas of repair which are involved. The first, and generally applicable, is structural: that moisture will damage plaster, and may cause the keys to break. If this is caught early enough, while it is tedious to repair, it isn't really all that hard. If it isn't, or if it is a ceiling (nothing like half the room's ceiling come down... !) it can get hideously expensive, and the last thing you want in an historic property is to have to resort to drywall because you can't afford plaster. The other area of repair is for contents, and this depends a lot on what is in those spaces. If they are mostly sort of storage for oddments you are not using, not a big deal if they get musty or mildewed. On the other hand, one property I care for has -- among other things -- a Steinway grand piano worth somewhere north of $100,000, which could be irreparably damaged even by mildew (I caught the problem in time, and it only cost me a good new SUV...). Books and paintings are also subject to damage which may or may not be repairable -- but never cheaply.