Boiler Working Overtime…

urbngasoutfitr

I have a slight dilemma(still investigating), but I have been keeping an eye on the boiler in our home which was installed a little before Christmas. I took notice of the actual run hours vs actual cycles run. The numbers are:

• Boiler run hrs: 156
• Boiler cycles: 907
• TT is a Honeywell CTN87 set at 3cph. 

Which puts the boiler working double it needs to be running at 5.8 cph. Quick EDR calculation brought me to 68,400 and our boiler is 70k BTU input. But the actual output says 59k BTU. Could the boiler possibly be undersized? 

I also set the circulator to overrun 10 minutes after a call for heat has been satisfied to disperse any extra heat lingering around in the boiler and back up to the radiators. 

Your help would be greatly appreciated,
Thanks 

Hot_water_fan

Sounds extremely oversized, that's all. EDR is not how boilers are sized for hot water systems. What's your general location? You can take heating degree days and this fuel usage to find your true heat loss. Since the boiler is a month old, you'll probably just get used to the short cycling. CPH doesn't mean cycles divided by hours. It means the most cycles per hour allowed by the thermostat. So if it was properly sized, you might only have 1 or less cycles per hour during the coldest weather.

EdTheHeaterMan

Steam systems need to be sized to the connected heating surface of the system. that is the way steam works because you only get one temperature from steam. HOT!

Water boilers can offer you several BTU output per radiator. A 20 EDR radiator will offer 4800 BTUh with a steamer. With a water temperature of 170° in that same radiator you will get only 3000 BTUh. At 140° water temp = 1800 BTUh. So the correct way to size a water boiler is to use the actual heat loss of the building and match with to the AHRI Net (Formerly I=B=R Net) boiler rating.

EBEBRATT-Ed

@urbngasoutfitr

Need more information. Is this steam or hot water? If it is steam and you calculated the EDR correctly and converted it to btu then you do look undersized. What type of boiler

urbngasoutfitr

@Hot_water_fan does the actual output of 59KBTU satisfy the EDR? Or the 70kBTU input? The calculation I did was to find out how many actual cycles the boiler ran during that hour the boiler took to satisfy the home’s temp, but I see that there is much work to be done here on my part. Much appreciated, btw we are located in SE Pennsylvania, Philly  

urbngasoutfitr

@EdTheHeaterMan so my calculations are incorrect per the boiler, because it is hot water & not steam… I will recalculate & get back to you on that, thanks! 

urbngasoutfitr

@EBEBRATT-Ed boiler is actually hydronic. Crown AWR 70k 

Hot_water_fan

does the actual output of 59KBTU satisfy the EDR? Or the 70kBTU input? The calculation I did was to find out how many actual cycles the boiler ran during that hour the boiler took to satisfy the home’s temp, but I see that there is much work to be done here on my part. Much appreciated, btw we are located in SE Pennsylvania, Philly

The EDR isn't relevant here as you want the heat loss to size the boiler. Looks like you're about 2x oversized using a quick fuel usage analysis, assuming the run hours are from 12/24 to 1/17.

EdTheHeaterMan

urbngasoutfitr said:

@Hot_water_fan does the actual output of 59KBTU satisfy the EDR? Or the 70kBTU input? The calculation I did was to find out how many actual cycles the boiler ran during that hour the boiler took to satisfy the home’s temp, but I see that there is much work to be done here on my part. Much appreciated, btw we are located in SE Pennsylvania, Philly  

Go Birds!

Go Crown Boiler

KC_Jones

You size hot water boilers by doing a manual J heat loss of the building, nothing to do with radiation.

The cycles will be a function of boiler size, to the heat loss of the building, but also the out door temperature on a given day that impact the heat loss of the building on a daily basis. The manual J heat loss calculations give the heatloss for the design temperature of the area the house is in. My area (south central PA) that is 7°, even though we will get colder than that on occasion. Design covers something like 98% of the coldest temperatures. Don't quote me on that percentage as I can't remember exactly, but it's the upper 90's.

mattmia2

Since we have had a very mild winter it may not be 2x oversized but probably is significantly oversized. With the mass of cast iron radiators connected to it I would be concerned that it runs long enough cycles that the boiler gets hot enough to boil off any condensation. You probably need some sort of a return water temp protection scheme if you don't already have it.

urbngasoutfitr

Hot_water_fan said:

does the actual output of 59KBTU satisfy the EDR? Or the 70kBTU input? The calculation I did was to find out how many actual cycles the boiler ran during that hour the boiler took to satisfy the home’s temp, but I see that there is much work to be done here on my part. Much appreciated, btw we are located in SE Pennsylvania, Philly

The EDR isn't relevant here as you want the heat loss to size the boiler. Looks like you're about 2x oversized using a quick fuel usage analysis, assuming the run hours are from 12/24 to 1/17.

Is there a reference for this material on how to calculate for myself? Also any solutions to this issue without accelerating wear & tear in the future? Thanks this helps a lot! 

urbngasoutfitr

@KC_Jones duly noted. I’m actually looking up the manual j load calculation manual as we speak. The heat has been fine since it was installed, but I’m glad I noticed this before it was too late. An oversized boiler will not suffice unless I can remedy the situation without removing the boiler at minimum. 

urbngasoutfitr

@mattmia2 that’s exactly what I am trying to figure out now at this point. Some type of remediation for this miscalculation. Because the boiler is here to stay. We did some renovations last year to the downstairs which gave us some warmer indoor temps bc we added insulation, but the upstairs is still plater & lathe. I know all this plays a role I just have to get to the bottom of it. Thanks! 

Hot_water_fan

Is there a reference for this material on how to calculate for myself? Also any solutions to this issue without accelerating wear & tear in the future? Thanks this helps a lot!

It's this method. Does this boiler also make Domestic Hot Water? If so, the heat loss is a bit less.

https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

Solution wise, not much you can do. You could install a buffer tank to length the cycles, but that's not cheap and doesn't change the fundamental oversizing. There aren't usually cast iron boiler sizes between 59kbtu and 30kbtu, so you'd have to be a bit undersized if you downsized. It probably wouldn't be noticeable, but I'd just live with the oversizing for a few decades.

Matt_67

On the bright side - if you've done the math right on the radiators the boiler won't short cycle during the call for heat. (Radiator heating capacity is greater than boiler output) You'll just have more variation in the house temperature and more cycles. If the house is comfortable I wouldn't worry about it too much. It would be nice if the industry could give us a little more variety in the smaller boiler sizes.

urbngasoutfitr

@Hot_water_fan the boiler is strictly for heat, no domestic hot water. I actually did some calculations on the heat load & the highest load I came out with was 49,500BTU (that was pushing the limit) adding up all square footage, taking into account windows & doors, bedrooms, etc. Roughly 50kBTU in which I would say our boiler is a tad oversized. 

urbngasoutfitr

@Matt_67 the house is definitely on the comfy side, sometimes opening a window just to dissipate a little heat on colder nights because the upstairs can be brutal on a below freezing day. But otherwise I guess you’re right. My new calculations brought me between 39 & 45kBTU, they definitely don’t have smaller boilers but we’ll live. Waiting on some test tools in the mail anyway so I’ll be able to tune the burners a bit & get an updated thermostat if that even helps. Thanks 

urbngasoutfitr

A net AHRI rating of 51MBH 

Hot_water_fan

@Hot_water_fan the boiler is strictly for heat, no domestic hot water. I actually did some calculations on the heat load & the highest load I came out with was 49,500BTU (that was pushing the limit) adding up all square footage, taking into account windows & doors, bedrooms, etc. Roughly 50kBTU in which I would say our boiler is a tad oversized.

Yeah those calculators can be wonky. You have to account for a lot of things that are pretty much unknowable or make unhelpful assumptions which result in being 50% too big. That's why I prefer the fuel usage, plus it's quicker. Regardless, you'll be okay.

EdTheHeaterMan

There are 2 ratings on a furnace. The input is how you size the gas pipe or the nozzle on oil heat. The output is what you actually get to use, or what leaves the heater. The efficiency of the heater has a lot to do with that. A furnace the has 100,000 BTUh input at 80% efficiency will have an output of 80,000, BTUh.

Boilers have 3 of these numbers. Input is for sizing the gas pipe or nozzle, output is based on the efficiency as in a furnace, and NET is what you use for selecting radiator size based on the Heat Loss Calculation. The numbers are actually called Gross Input, DOE Output and AHRI NET (formerly I=B=R NET). Once you determine the Heat Loss of a building, then you select the amount of radiation and then the boiler based on the NET BTUh number.

Older boilers will only have Gross and Net numbers. the DOE output was added in the 1970s in order to compare boilers and furnaces. Like MPG on a car, the Dept. of Energy needed that number in order to have a level playing field for comparison. With furnaces, the placement of the duct work needed to be considered when designing the furnace size. Cold attic, or warmer basement or within the conditioned space, along with the ductwork insulation was all taken into consideration when choosing a furnace. Boilers had the Piping and Pickup loss or 15% already included in the I=B=R NET number.

Steam actually had a different I=B=R NET number because the piping and pickup number is closer to 30%. And that is one of the reasons that steam boilers use the EDR for sizing and water boilers use Heat Loss Calculation for sizing. As you tighten up the home, better windows, more insulation, sealing the cracks and crevices in the building, you can use a smaller water boiler. Just lower the water temperature and you get a lower radiator output. The steam boiler is still connected to the same pipes and radiators no matter what you do with the structure. Sealing and insulation will still lower the fuel bill by reducing the time the heater is operating, but you still need the steam to get to the radiators and that does not change what is going on inside the radiators, boiler and connecting pipes.

So, with this new understanding, you can now determine how the EDR in your home converts to BTUh required, and determine the needed water temperature to make that happen.

EBEBRATT-Ed

@urbngasoutfitr

Set your high limit at 190. Install a low limit circulator control. Bring on the circulator at 140 degrees and off at 130 degrees. This will protect the boiler against condensation.

Keep the boiler as a cold start. The high limit must stay in the circuit at all times. Use the thermostat (and reduce the cph to get longer run times and less cycling. Wire the thermostat to start the boiler And to put the low limit/circulator control in the circuit. This will require a relay. Use a strap on aqustat to allow the circ to run down to 130 when the thermostat opens

mattmia2

If you don't make sure it gets hot enough to boil off condensation every cycle, that is the only thing that will cause a noticeable reduction in life. More, shorter cycles otherwise just means you might be replacing a vent damper or circulator relay or gas valve a decade sooner.

The cadillac of system would be to use a thermostatic valve to keep the boiler return water above condensing temp and an outdoor reset control and mixing scheme to keep the supply water temp at a temp that matches the load but that is likely not particularly cost effective.

nicholas bonham-carter

"opening a window just to dissipate a little heat on colder nights because the upstairs can be brutal on a below freezing day"-is that too hot, or too cold?
Maybe some balancing is needed.--NBC

urbngasoutfitr

@nicholas bonham-carter that means it’s too hot. Our home is on the smaller side so most of the heat rises. We renovated the downstairs to an open concept removing a wall in which the heat spreads evenly downstairs but towards the end of a call for heat the upstairs is super toasty 

urbngasoutfitr

@mattmia2 sounds like a challenge which I’m up for, but as you said, later on down the road. We’re actually finishing the basement so maybe I can add some elements to the system to kind of match up to the boiler size instead of electrical baseboard heaters. 

EdTheHeaterMan

Adding heat emitters to that boiler will not make the boiler the correct size for the home. Will the basement temperature actually get hotter that the current temperature? By how much? More that 8°? The basement load should already be part of the heat loss calculation. Adding radiators will just put the heat in the basement. That heat will eventually get upstairs by convection currents. (that means that hot air is lighter than cool air, so the hot air rises). In order to balance the heat in the different levels, you might want to think about how to hard (or easy) it is to zone the different floors radiators in the home. That will send less heat to the upper radiators as the lower floor heat rises.

EdTheHeaterMan

urbngasoutfitr said:

@mattmia2 sounds like a challenge which I’m up for, but as you said, later on down the road. We’re actually finishing the basement so maybe I can add some elements to the system to kind of match up to the boiler size instead of electrical baseboard heaters. 

Be careful when walling off the boiler. Combustion air coming from the basement may be enough now. If you wall off the boiler room and seal the door to the rest of the house, that smaller room will become a confined space. That means the room will not have enough air to provide sufficient oxygen for combustion and the gas will burn rich. That will make soot form and block the heat exchanger. Then carbon monoxide could enter the home and make everyone inside sick enough to wake up dead the next morning.

EdTheHeaterMan

Took a closer look at the title of your discussion


Are you paying overtime rates? That would be time and a half for anything over 40 hours and double time on Christmas and New Years day. Do you include MLK day too?

urbngasoutfitr

@EdTheHeaterMan I will find out how much overtime has been paid once the gas bill comes this month lol 😂 but if I add anymore emitters to the system & wall off the boiler, I would have to install fresh air vents top & bottom and also louvered doors to keep the same air.  

EricPeterson

For the overheated rooms, consider installing TRVs so they are not running full blast all the time.
TRV=Thermostatic Radiator Valve
You would need to drain the system to install these, so after the heating season, but it's worth it.

Eric Peterson

mattmia2

urbngasoutfitr said:

We’re actually finishing the basement so maybe I can add some elements to the system to kind of match up to the boiler size instead of electrical baseboard heaters. 

I would tee off and add a second zone for the basement with its own circulator and thermostat, put a flow check in each zone and run the basement separately. Probably a zone panel wold be the best way to control it.