New boiler and slant-fins

Hot_water_fan

Can you explain one more time that isn't my lowest output boiler, or something very close to it?

Because the odds of it being sized right at installation are pretty low. The actual usage shows you want happened in reality - it’s equivalent to sitting in the basement 24/7 with a stop watch . 

fentonc

The BTU output of your system is dependent on the water temperature - say it outputs 84.6K BTU/hr with 180F water coming out of your boiler. If your maximum actual heat loss for your house was only 38K BTU/hr, that means that it would only run 38/84.6=45% of the day on the coldest day of the year if you were using 180F water. The BTU output decreases with water temperature, so maybe you actually only need 140F water to output 38K BTU/hr on the coldest day of the year, and most of the year you could get away with 120F water (since your heat loss goes down with warmer temperatures). With a condensing boiler, if the water temp is below 135F or so your efficiency goes up significantly by causing the flue gases from your boiler to condense. Most modulating/condensing (mod/con) boilers support an 'outdoor reset' scheme, where an outside temperature probe is used to set the water temp to keep it as low (and as efficient) as possible.

TerrS

@fentonc thanks. I don't want to rehash too much here, but I can tell you I freeze when the out-side temperature is <35 degrees and my water temperature is not at least 180 degrees. With my aqua smart, and temperatures above 35, yes, I have seen between 160 and 175. This is why I am leaning away from the modulation boilers. If I had any other types of baseboard heat, not all fins, then we could have a discussion, but the only way you get the 95% is with return water around 140 degrees or lower and I NEVER ever see those temperatures on either my boiler Guage or aqua smart controls. 

If I wanted to spend even more money I would replace 1/2 of them with buderus rads and could make my house Miami with 160 degree water. But they are around $600 each with fittings and depending on size, to try to get ROI of that maybe 10%. Meaning boiler I am leaning to is 85% efficient. And difference of condensing boiler, that doesn't condense more days or let's say 2.5 months out of 5 to be generous. Doesn't return money until year 10.

hot_rod

Keep in ming the mod part of mod con. A 120 mod con can regulate its output from 12,000 to full output. With outdoor reset dialed in perfectly, a mod con could almost run non stop, modulating constantly to the changing load of the home. Think of it as a cruise control on your heating system.
An 85% non-con boiler will cycle on/ off a lot on mild days

I'm not sure how to put a $$ amount on that difference in operation, common sense is less cycling of equipment= longer life. Plus the small fuel savings. A good mod con comes with a lot of control adjustability, ODR, ramp delay, derate, online monitoring for when you are in Miami

TerrS

hot_rod said:

With outdoor reset dialed in perfectly, a mod con could almost run non stop, modulating constantly to the changing load of the home.

An 85% non-con boiler will cycle on/ off a lot on mild days I'm not sure how to put a $$ amount on that difference in operation, common sense is less cycling of equipment= longer life. Plus the small fuel savings. A good mod con comes with a lot of control adjustability, ODR, ramp delay, derate, online monitoring for when you are in Miami

I need a clarification on this, maybe just a typo. But if you said a mon con might run consistently all day, just adjusting burner output based on outside temperature and load.

However from what I understand if I need 180 water, or close to it, it would probably not modulate down much and still keep up my heating demands.  Then I have to add in there is no or very little condensating/ efficiency that would happen because the water would never get to the 135/140 temperature needed.

So wouldn't that cause more wear and tear on the mod con?

Hot_water_fan

However from what I understand if I need 180 water, or close to it, it would probably not modulate down much and still keep up my heating demands.

It can produce 180 degree water at less than full fire. It also would only need the 180 on the coldest days.

KC_Jones

TerrS said:

@fentonc thanks. I don't want to rehash too much here, but I can tell you I freeze when the out-side temperature is <35 degrees and my water temperature is not at least 180 degrees. With my aqua smart, and temperatures above 35, yes, I have seen between 160 and 175. This is why I am leaning away from the modulation boilers. If I had any other types of baseboard heat, not all fins, then we could have a discussion, but the only way you get the 95% is with return water around 140 degrees or lower and I NEVER ever see those temperatures on either my boiler Guage or aqua smart controls. 

If I wanted to spend even more money I would replace 1/2 of them with buderus rads and could make my house Miami with 160 degree water. But they are around $600 each with fittings and depending on size, to try to get ROI of that maybe 10%. Meaning boiler I am leaning to is 85% efficient. And difference of condensing boiler, that doesn't condense more days or let's say 2.5 months out of 5 to be generous. Doesn't return money until year 10.

I think there is still a point you are misunderstanding, at least based on everything you have posted it seems that way.

The water temperature alone is not the BTU output of the baseboard. It is water temperature and TIME because the output is in BTU/Hour. The example you gave of the boiler firing 4-5 times for 6 minutes at a time comes out to about 50% run time. Once the boiler and pump stop, because as you stated the thermostat is satisfied. A majority of the heating stops. Baseboard is low volume and cools down fairly quickly.

So output with 180° supply water with at 15° (I believe you mentioned that) delta T gives an average water temp of 172.5, for discussion let's use 170 because that is listed on the rating chart. at 170 the output is 510-540 depending on what flow you have (I don't know what you are getting).

So, if we start with 50% of the output that puts the water temperature required to about 140 based on the above numbers. So if you were to go to a modulating condensing boiler that is properly sized it would run continuously at 140° and it would keep you warm. This is the most efficient way to run, and it should actually be the most comfortable.

To put it another way, same baseboard, same house, 180° water being supplied 50% of the time, is the same output as 140° water being supplied 100% of the time.

The only way you need 180° water is if the boiler and pump are supplying 180° water continuously 24/7 and not stopping ever. Basically the thermostat is never satisfied. The minute the boiler and pump cycle, the output of the system is dropping off and you are not getting the full calculated output of the baseboard.

This is why a heat loss of the building is critical, that dictates the actual amount of heat required. The heat loss dictates boiler size, the amount of baseboard will help calculate required water temperatures to deliver those BTU's to the home. More baseboard relative to the heat loss and the lower the temperature you can run, on a continuous basis.

TerrS

@KC_Jones I am not an expert at this, like at all.. but what I can tell you my first 2 winters in the house with 170 degree water we froze. Once I reset to the 180, we got enough radiant heat off the fins to stay warm. And to be honest until the utility cost this past winter never really paid attention.

This past winter I started paying attention. I mean to the point I sat by the boiler for 1-2 hours. Counting how long and how many times it ran. Like I stated I can't keep my house warmer than 68 or I would use another 100 therms a month, instead of my 200 now. The aqua smart seems to have helped but I only installed it the beginning of February. So 2 months of data. Showed most days at 180, with avg temp in Feb 29 degrees outside.

The test I did Before I bought the aqua smart was to install a low limit to never do a boiler cold start. For 1 week I had quicker access to heat because my water was kept at 110. And that took the 4-5 runs an hour to maintain that. So cold starts I wait 30 minutes to get 180 water. With water already at 110, I waited 15. That cost me an avg of an extra 3 boiler runs per hour.

I am questioning your thinking. Not because of your calculations. But because while the boiler is firing I need 180 degree water to radiate those 650 btus per ft. So I have to account for that.

Also my loop runs are short, probably 60ft of runs. So my return water doesn't drop that much but I don't fire the boiler until it drops 15 degrees. Then rinse/recycle.

Real world experience, beats the calculations for keeping the house warm. Again not questioning those,

It basically comes down to price to install boiler, vs the quantified possible savings, and to date, absolutely no-one can do that. Too many variables especially condensing and return water.

Where as I know my old 32yr old boiler is only around 78% efficient. The possible new boiler I will drop in size by 30k btus and increase to 85% efficiency. And it has all the built-in smart controls and ODR.

I need a hvac to give the money back guarantee lol. I will hold my breath

JakeCK

You need to get off of the 180f water temp. Period. Sorry to tell you this. Please listen to what everyone is telling you.

This is pure physics. 

JakeCK

Also there is substantial savings between a 100k btuh boiler and a 50k btuh boiler. Possibly more then you would see over it's life time in fuel savings.

TerrS

JakeCK said:

You need to get off of the 180f water temp. Period. Sorry to tell you this. Please listen to what everyone is telling you.

This is pure physics. 

Please tell me how I can do that? I have looked at all the slant-fin documents and lowering water temp, means lower radiant heat being given off. 

If I had the time and extra money to like I said swap out to buderus rads or a higher efficiency base board system, then I would 100% agree with everyone and go mon con.

I dont see how to get around the issues I see in water temperatures..

And one thing this thread has proved is I don't need a 150k/113k btu boiler. On the high end a 120/101k btu, but more like a 92/78k btu would be plenty.

KC_Jones

Is your system pumping 180° water through the baseboards 24 hours a day seven days a week?

TerrS

KC_Jones said:

Is your system pumping 180° water through the baseboards 24 hours a day seven days a week?

No but if you ask if it does When the thermostat requires heat, then yes it does.

KC_Jones

TerrS said:

KC_Jones said:

Is your system pumping 180° water through the baseboards 24 hours a day seven days a week?

No but if you ask if it does When the thermostat requires heat, then yes it does.

The output on those baseboard charts is BTUs per hour. You need to understand this you cannot, absolutely cannot, look at the water temperature only. When the pump stops pumping water the output drops, like a stone. So unless you are pumping 180° water 24 hours a day seven days a week all winter long you are factually not getting the output from the baseboards that is on those charts.

you are essentially only getting the output from those charts while the pump is running. Baseboard is low mass, it cools down relatively quickly.

The reason I know this is not going on in your home, is because if it was you would either be cooking yourself in the shoulder seasons, or absolutely freezing in the dead of winter. The output from the system is variable, and absolutely has to be. 

You also stated that you keep it at 68°, but imply that you could go higher by burning more fuel. That fact also states to me you are not using the full output of the baseboard, there is more in reserve. The extra comes from longer run times.

Jamie Hall

At some risk of asking a question which people think has been answered, I'lll ask.

Does your thermostat always stay on? Or does it turn on and off, even on the colder days?

The thermostat on the wall, that is. Or another way of asking that, on the colder days is the thermostat on the wall ever satisfied?

(I think somewhere you said that you could turn the thermostat up and the house would get warmer, but at the expense of more fuel. That sort of answers the question, but I'd like a straight answer please.)

(And of course it takes more to get the house warmer. That should be obvious.)

Now if not, you have the boiler bouncing off the aquastat upper limit -- I believe you mentioned that the temperature drops about 15 degress and then it restarts.

If the thermostat is never satisfied, that means you need the full output of those 80 feet (I believe you said) at the 180 F water you are feeding them, and let's assume -- in the absence of a clear answer, that that is in fact what happens. That full output is around 51,000 BTUh. There is simply no possible way that you can get more power out of them. That's pure physics. That also means that there is no way you can put more power into them. That's also pure physics. If you try, all that will happen is that the circulating water temperature will rise -- and the boiler aquastat will turn the boiler off until the circulating water temperature drops. Then it will restart. That's quite normal.

Put in a bigger boiler, it will fire for less time and be off longer. Put in a modulating boiler, and it will adjust its firing rate down to match the heat output of the radiation. Take your pick.

To go one step further here, changing the boiler size will not affect the heat loss of the house. If your house does, in fact, require that 51,000 BTUh to keep it warm, that's what it's going to require, regardless of boiler size. A bigger boiler will, however, be less efficient as it is running shorter cycles to supply that power, so it will use more gas. How much more? Not really that much, probably. But more.

TerrS

@KC_Jones I think I need to give up.

When my thermostat is calling for heat, 2 things happen. The boiler lights and Pump kicks on after a 2 minute delay. It will now heat the water the first time to 180 degrees, Unless the aqua smart knows the last x number of times the thermostat was satisfied with only lets say 170 degree water. The pump never ever shuts off until 3 minutes After the thermostat is happy, to take advantage of water that might have just been heated.

So lets say that is 1hr in total time, then yes I have transferred 650btu per foot over that 1hr period, unless the aqua smart said it can provide enough heat with 170 degree water, which means the boiler didn't light again. As soon the boiler lights again the aqua smart raises the water temperature and this is the new set point.

I have sat and watched this happen. It might not be right but it's what's happening in my current configuration.

KC_Jones

The time the system has a off factors into the baseboard output to heat the house.  You stated the thermostat satisfies, which means the system turns off, the off time is part of the output of the baseboard, I think that is the piece you are missing here.

Again it’s btu per hour, all the hours, not just when the pump is running.  This is why I asked the question about 24/7.

TerrS

@Jamie Hall on a cold day my boiler will run for at least 1 hr until the thermostat is satisfied, depending on where the house starting temperature was at, lets say 64 degrees because that's my setback from 10pm-5am. So a rise of 4 degrees over that 1hr span.  This is when the thermostat switches to day mode and 68 degrees. During the day, my thermostat might call for heat 3-4 times an hour, again depending on the out-side temperature. But might only run 10 minutes because the house only needs to come up 1 degree back to 68.

JakeCK

You say the boiler will run at least an hour on a cold day. Is that the time the t-stat is calling for heat, circulator on, boiler firing? Or does the boiler bounce off the aquastat? Which would mean the pumps would keep running, t-stat would continue to call but the burners are off until it cools below set point?

TerrS

@jakeck yes the boiler will stop firing when the water hits it's setpoint determined by the aqua smart. Everything else is true. Boiler will keep cycling heating the water until thermostat is satisfied. 

My last comment because maybe I will just never understand this. But I can't size my boiler where it takes 2 hours to raise those 4 degrees. When my house is calling for heat, I need to be able to provide enough btu's to satisfy the demand and at whatever water temperature is required to do that. I understand i don't want to over size, because of short cycling and a waste of extra gas, but sizing to small, I think would take much longer to provide the heat needed.

Jamie Hall

You shouldn't be a bit surprised that it takes 2 hours to heat the house 4 degrees. That's the nature of it. It takes a certain amount of power -- BTUh -- to satisfy the heat loss of the house at a given temperature. It takes a certain amount of additional power - BTUh -- to change the temperature of the house and its contents.

Perhaps if we use a completely different set of examples, it may be a bit clearer. Let us consider your car. And let us say you are cruising along a nice flat road at 40 mph. You have your foot on the accelerator at a certain angle. Now you decide you don't want to go 40, you want to go 50. How do you do that? Well... it takes more power, so you stomp on the gas. But -- unless you have a Corvette -- you don't get to 50 right away, even foot to the floor. It takes time. Now when you get up to 50, you back off the gas -- but not quite to where you were; it takes a little more power to go 50 than it does to go 40.

So your house is at 64, and the boiler and pumps are running just enough -- controlled by the thermotats -- to hold that temperature. But you now decide to bump it up to 68, so you crank up the thermostat. Now the pump and the boiler turn on. The pump will keep running all the time until the thermostat reaches 68 and says stop. The boiler will cycle on and off to provide the power to the fin tubes. You get up to 68 and the thermostat -- and pump -- shut off, and the boiler, if it was on, also shuts off. Now when the thermostat calls for heat again, the pump turns on, the boiler senses that hot water is needed and it turns on, and the temp rises a little and the thermostat turns off again. Rinse and repeat.

Thinking of boiler size, again let's go back to the car. In fact, let's take my beloved Lady, a Buick Skylark GS Stage II with about 450 horsepower. Do I need that 450 horsepower to cruise at any steady legal speed? Um... no. Hardly. Do I even need anything close to it to accelerate reasonably briskly from, say 65 to 90? Um... no. The car will perform perfectly well in that regard on about 150 horsepower, max. So do I need that bigger engine? I do not. For almost all legal purposes, the car would be just fine with a 150 hp V6, and be a lot cheaper to run. (It's kind of nice at your local quarter mile, though, to blow the doors off pretty much anything else you can drive to track). And so it is with your boiler. Will a bigger boiler heat the house? Yes, it will. Will it heat it any faster? No it won't (You're limited by your radiation, not your boiler)(to continue the analogy -- Lady's top speed is 130, but not limited by the engine -- the tires won't take it). Will it cost more to buy and run? Indeed it will.

Your call.

TerrS

@Jamie Hall  yep I was getting to that analogy.  so you're right, almost every car can get to 100mph, given enough time. When we are talk heat, the sooner the better. So in my ideal world in, using a 1hr time frame, with my configuration i can produce around 84600btu's from my fins given 180 water. This is proven because in 1 hour right now I can heat my house 4 degrees. The problem now is I am spending 150k btu to get 113k btu out, it's a waste on all fronts, so the boiler cycles and waits, and it's very possible it will take more energy doing that. And that's been stated here a few times.

So if I buy enough btu's or maybe slightly under that 84600btu's number, I should be able to heat my house those 4 degrees and still in that 1hr time-frame, but use less energy. Now if I buy much less, lets say 50k btu, I have now extended that time to raise my house temperature up those 4 degrees on cold days, which we have many here in Pittsburgh. Yes, It will eventually get there but I will be cold until it does.

Hot_water_fan

@TerrS you got it. Why do you use a setback? 

JakeCK

Continuing with the vehicle analogy, some mustangs are known to blow their driveshafts right threw the floor boards at about 130mph. In other words you could put a blower on top of that engine and almost double the power to the wheels but unless you build out the whole car, it's only going to make it so you can blast your center console into orbit a little quicker. 

TerrS

@Hot_water_fan so the main reason is I am 10,000 degrees at night, call it whatever, but it is Harder to get colder when you are already at the minimum clothes/covers. You can always add covers. The other is too save on those gas bills. Now during the day I like it to be around 70, but that comes at a cost. I will probably always have the night setback, but instead of another one from 10am-3pm weekdays, I will get rid of that hopefully.

Jamie Hall

TerrS said:

@Jamie Hall  yep I was getting to that analogy.  so you're right, almost every car can get to 100mph, given enough time. When we are talk heat, the sooner the better. So in my ideal world in, using a 1hr time frame, with my configuration i can produce around 84600btu's from my fins given 180 water. This is proven because in 1 hour right now I can heat my house 4 degrees. The problem now is I am spending 150k btu to get 113k btu out, it's a waste on all fronts, so the boiler cycles and waits, and it's very possible it will take more energy doing that. And that's been stated here a few times.

So if I buy enough btu's or maybe slightly under that 84600btu's number, I should be able to heat my house those 4 degrees and still in that 1hr time-frame, but use less energy. Now if I buy much less, lets say 50k btu, I have now extended that time to raise my house temperature up those 4 degrees on cold days, which we have many here in Pittsburgh. Yes, It will eventually get there but I will be cold until it does.

OK. You have two different considerations here. You have the power the boiler can produce, and the power which your radiation can deliver.

Your bigger boiler will NOT heat the house in less time -- you can only heat it as fast as the radiation will allow. So -- the boiler will have to cycle on and off. If the boiler is exactly matched -- or nearly so -- to the radiation, you will get the same time for temperature rise -- and, perhaps more to the point, you will use almost exactly the same amount of fuel. The aquastat will prevent the bigger boiler from running full time; it will stop from time to time to let the radiation catch up If you drop the boiler too far, then it becomes limiting instead of the radiation, and you may not be able to raise the temperature at all. You may, in fact, not be able to maintain it.

Let's look at cars again. Consider my overpowered Lady. Her biggest limitation in accelerating from a standing start is, again, the tires. If I get too frisky, they will just spin and I have to back off a bit. Not enough traction (lots of smoke, though...). But take another example. Many moons ago I bought myself a 1955 VW convertible (bought it new, my first "own" car -- there are times when I wish I still had it!). It had a whopping 36 horsepower on a good day -- and that simply wasn't enough to maintain speed, never mind accelerate, up a steepish grade. Like the hills on the Massachusetts Turnpike...

You have to consider the whole system, not just one component.

bburd

I am hesitant to add more complication here, but one key point has been overlooked.

The OP has a high limit aquastat setting of 180°F. That aquastat probably has a 10° differential. That means it will cut the burner out at 180° and cut it back in at 170°, giving an average supply water temperature *leaving the boiler* of 175° F.

We can ignore minor losses in the piping, which I assume is within the house.  The OP stated that the temperature drop (delta T) through the system is 15°F. That means the *average water temperature in the radiators* when the system is running full blast on a continuous call for heat is 175-(15/2) = 167.5°F, not 180. This is the number that should be used when consulting the  radiator rating chart.

This is assuming the aquastat is accurate. It’s probably not too far off, but an infrared thermometer reading off a piece of tape stuck to the supply pipe would confirm this.

TerrS

@bburd at the risk of killing this dead horse once I again, I have a few additional comments.

First my aqua smart is set to a max of 185degrees and only a 10 t-diff, i had to reverify this today. This is because I noticed a 20 water temperature difference between what the boiler Guage stated and the aqua smart thinks. On one my coldest days in Feb, I watched the setup for about 1hr to make sure it was running as I wanted and not going over temp.

You are right that I need to buy an infrared heat scanner to hopefully verify my supply/return temperatures with what we all think.

I will tell you when I had the l8124 installed, the boiler guage was always going to 180. I asked another question on here in one of my threads and everyone said don't worry about the difference if the house is still staying warm.

Last comment in looking at the basic h3 slant-fins, they range from 650btu/170 water to 730btu/180 water.

If my avg stays in that range it seems my house will heat quickly and stay as warm as I set the T-stat for.

The current boiler size is way over by at least 40k btus. So a waste of energy that is way over my maximum needs.

So I have enough information now to make a better informed decision. So thanks everyone!