Is my boiler operating properly or is it defective/undersized?

[Jean-Sebastien Stoezel]

Hello,

About 8 years ago I replaced an older Smith boiler with a new, well known brand. The old boiler was rated for 210kBTU, the new one is rated for 167kBTU.
Comparing the effectiveness of the 2 boilers, the old one used to put out a tremendous amount of heat, to the point where some rads were too hot to touch. It would hit the set point of 180F and would cycle.
The new boiler barely reached 150F, and that would be after a forced run of over 90min, by setting the thermostat to a high temperature value. In normal operation the boiler would require the bypass to be over half open with a slower circulator speed, otherwise it would not build up heat.
I was told this is because the piping around the boiler was 1" diameter, which throttled the boiler. The minimum pipe diameter recommended by the manufacturer of the boiler is 1-1/4". The low water temperature means that on cold days, the boiler cycles for 30min on/off.

Recently I had the same plumbing company replace the surrounding piping with 1-1/2" piping, which is 1/4" over the minimum piping. They also installed a larger circulator. This was to make sure rads on the 3rd floor of my house would get hot water, and also to speed up the round trip time of the water.
After this modification the boiler is operating slightly better. I can close the bypass to less than 1/4, though even after a forced run of 90min the water barely hits 160F, and once it reaches this temperature there is little to no temperature gain. The delta between supply and return is about 10F up until about 140F on the supply, and the delta goes down from there.

This boiler has been acting like this from the get go. I have had the plumbing company check twice with the manufacturer whether this boiler was the proper size, based on rad count, age of the house and insulation levels, number of stairs in the house. They are insuring me that this boiler is the correct size (they had initially installed the step down size and it was too small, and 167kBTU still is not the 210kBTU the old boiler used to be - which is a big gap even when you take into consideration the efficiency difference between old and new).

Every service technician from different heating companies I have hired to service this boiler keep setting the water temperature set point to 180F, though this temperature will never be reached, unless there is some sort of problem including circulator failure. Every single technician, including technicians from the company that installed the boiler have told me that if the boiler cannot reach 180F it has to be undersized. Even the manufacturer website recommends and average water setpoint of 180F, and increase this value on cold days to 210F.

And so, if the boiler is properly sized (dixit the manufacturer and the installer), is it that this boiler has been defective from the get go?

Where does the 180F water temperature value come from? What is a reasonable amount of time that this temperature value should be reached, and from what starting water temperature? How much bypass flow should be used to achieve this temperature?

Thank you for your help.

 

[Fitter30]

Brand and model # of boiler? What are your heat emitters - fin tube, radiators or ? Take some pics of the boiler, piping, expansion tank and pumps. What is your outside temp 24* f? Has anyone checked the gas pressure at the burner or is it oil fired?

 

[Sponsor]

 

[Jean-Sebastien Stoezel]

Thanks for the reply. I am not sure how to add pictures so I will describe the system from the boiler up to the manifolds. To answer your questions:
- Weil-McLain CGI-6, 8 years old,
- Cast iron rads, over 3 stairs. Various sizes and shapes. I provided rad counts, column numbers, radiator dimensions to the heating companies who provided this to Weil Mclain in order to size the boiler. This is a high volume system, the house is 2400sqft, a total of 16 rads.
- Piping is 1-1/2" out of the boiler, from the boiler up on the supply, expansion tank is a Flex 2 (suction side), then circulator is a Grundfos 26-99, then 1" bypass to return, from there there's an horizontal manifold for both the supply and return made of copper, 5 supply/return circuits going to black pipes of large diameter (about 2"). A pretty simple system overall. Operating pressure is 19psi cold, 23psi hot.
- Outside temperature currently is in the mid 20s (very mild for the season), typically we should be in the minus F temperatures.
- Gas pressure was checked after the boiler was first installed, when I reported it was not operating as well as the one it was replacing. Gas pressure was assessed to be within normal/expecting range.

 

[Jean-Sebastien Stoezel]

Figured out to upload a picture

 

[Fitter30]

Minimum boiler water temp return 60* c. Bypass between supply and return can be closed. Next is checking btu rating of boiler, 3600 x 1000 divided by timing the gas meter 1 cu ft how many seconds it takes. Can vary a little because how much lp gas company put in. Can check with them. With that digital thermometer measure supply / return temps of each zones and boiler.
looking for -6.7* to -1*c. Is that insulated line that runs under the pump going to expansion tank on floor? Whats the taco model?

 

[Jean-Sebastien Stoezel]

Minimum boiler water temp return 60* c. Bypass between supply and return can be closed. Next is checking btu rating of boiler look at pic. Btu per cu. ft can vary a little because how much lp gas company put in. Can check with them. With that digital thermometer measure supply / return temps of each zones and boiler.
looking for -6.7* to -1*c. Is that insulated line that runs under the pump going to expansion tank on floor?

Thanks for the reply. I can never reach that 60C water temp return particularly if the bypass is closed. To reach this temp I need to both fully open the bypass and partially close the supply isolation valve.

I am not sure how to check what the BTU per cu.ft. I am supposed to have a call with the plumbing company that installed this boiler and I will ask. I was hoping to gather more information about the operation and setting of this boiler before calling them.

This digital thermometer I designed myself, I had asked the plumbing company to install a pressure/temperature in the gauge on the return identical to the one on the supply and they said it was not necessary... Well it looks like it is now.

Yes, good eye the insulated line going to the back of the boiler is for the expansion tank.

I am confused by the procedure to follow to set the bypass valve. From this document: https://www.weil-mclain.com/sites/d...ual 1016 Web Version - Starting CP7531680.pdf
I believe I need to follow procedure described in 4d since this looks like the piping topology I have on my boiler, and this is a high capacity water system I believe.

I followed the procedure this morning, the only way I can get the return water to be in the 130F range is to fully open the bypass valve, and partially close the supply isolation valve. Lowering the circulator speed also increases the temperature.

If the isolation valve is fully open and I fully open the supply isolation valve the heating curve on the return dramatically flattens (the custom digital thermometer for supply/return also plots a temperature graph for each circuit) and barely reaches 120F after a 30min run.

 

[Jean-Sebastien Stoezel]

Here is a picture of the digital thermometer. Disregard the blue line, I cropped the picture just to focus on the graph. The red line is the return temperature. Time flows from right to left, so the right side is the latest measurement, the left side is the oldest measurement.
At the beginning of the run I had the bypass fully open and had the supply isolation valve partially closed. This follows the instructions in the boiler manual to maintain a minimum temperature of 130F on the return. As you can see the temperature increase rate was good and I could probably reach the 130F. But this is with the bypass fully open and the supply isolation valve half way closed, which seems wrong. I have 3 stairs and I am not sure I'd get sufficient heat with this setting on the last floor. The bumps you see on the far left are due to me playing with the circulator speeds (lo/mid/hi). The lower the speed, the higher the temperature increase rate.
Now the first drop in temperature is me opening fully the supply isolation valve. As you can see the return temperature drops significantly, and its rate is much less. This may not be evident on this graph since we're missing most of the first ramp on the left.
You may also notice that the temperature rate plateau eventually, this is around 120F.
The final drop is the boiler shutting down after about 30min.

I can try to make a nice plot with actual temperatures and different valve positions if this can help.

Thank you again for your inputs.

 

[Fitter30]

Minimum boiler water temp return 60* c. Bypass between supply and return can be closed. Next is checking btu rating of boiler, 3600 x 1000 divided by timing the gas meter 1 cu ft how many seconds it takes. Can vary a little because how much lp gas company put in. Can check with them. With that digital thermometer measure supply / return temps of each zones and boiler.
looking for -6.7* to -1*c. Is that insulated line that runs under the pump going to expansion tank on floor? Whats the taco model?

Read my post again my pic didn't come out so i wrote the timing of the gas meter formula. Slow the pump down to raise water temp.

 

[Reach4]

Minimum boiler water temp return 60* c.

Did you mean maximum? I thought low water return temperature was good.

 

[Jean-Sebastien Stoezel]

Read my post again my pic didn't come out so i wrote the timing of the gas meter formula. Slow the pump down to raise water temp.

Thanks for the headsup, I missed the formula. I will go out and measure the time in seconds of how long it takes to go through 1 cu ft of gas, I will do this at the next boiler run.

 

[Jean-Sebastien Stoezel]

Read my post again my pic didn't come out so i wrote the timing of the gas meter formula. Slow the pump down to raise water temp.

I took the measurements and observed something interesting. Maybe this is normal operation, I am not sure, I had never looked at my gas meter before. I only have the boiler on the meter.

What I can see is that there is an alternating time pattern to burn 1 cu ft of gas. One cu ft will be burnt in about 20.4s, the next cu ft will be burnt in 23.4s and so on. It is very consistent and repeating.

And so from your formula this would be 3600 * 1000 / 20.4 = 176470 or 3600 * 1000 / 23.4 = 153846 with a median value of 165158 BTU.
This seems to match the rating of the boiler (167kBTU).

 

[Fitter30]

Boiler gas usage is within specs as you now know. That 180* setting is usually what design temp would be at the coldest days. Here is a design temps for different cites looked at a couple cities - 33* c. Try closing supply side of pump ball valve till you get -1*c with bypass closed. That procedure for bypass is for a low temp radiate system. What type of themostat are you using brand and model? Boilers gas valve brand and model?
http://ashrae-meteo.info/v2.0/places.php?continent=North America

 

[Fitter30]

It's the gas provider that can tell you the btu content not the plumber.

 

[Dana]

Without knowing the total size of the radiation it's hard to say if the boiler is undersized for the radiation (probably not), but for a 2400' residence the boiler is all but certainly OVER sized for the design heat load, even in colder parts of Manitoba. Is this an uninsulated double-wythe brick structure with only single-pane windows (no storm windows)?

Using fuel-use against local heating degree-day data it's possible to directly measure the design heat load of your house using this methodology. Odds are pretty good you have enough radiation to make optimal use of a right-sized condensing boiler, but alas the CGI series isn't one of those.

 

[Dana]

Did you mean maximum? I thought low water return temperature was good.

Low return water temps are only good for condensing boilers. Chronic condensation on the heat exchanger plates of a cast iron boiler causes excessive corrosion, shorting the life of the equipment.

 

[Nebojsa]

Low return water temps are only good for condensing boilers.

Interesting reading. So i assume that my Triangle Tube Prestige Solo 110 is a condensing boiler,and the Weil-Mclain CGI-Gold seies 2 is not a condensing boiler.
I can assume that is why one can handle lower return water temperatures, while the other one requires a minimum of 130F

 

[Fitter30]

Condensate has a ph of 4 very acidic with ferris metal and copper it loves to eat. Most residential boilers use mechanical controls for controlling water temp. Every time a running boiler dips below 130* it's starting to condense. The other problem I've seen cracking and flaking of the cast refactory surounding the burner fire box. All manufacturers test their equipment in a lab not real world conditions.
Cast iron radiator btu chart
https://www.google.com/url?q=https:...FjAAegQIBBAB&usg=AOvVaw0cxL9WBZNKtKMMpSh3QhGQ

 

[Jean-Sebastien Stoezel]

Boiler gas usage is within specs as you now know. That 180* setting is usually what design temp would be at the coldest days. Here is a design temps for different cites looked at a couple cities - 33* c. Try closing supply side of pump ball valve till you get -1*c with bypass closed. That procedure for bypass is for a low temp radiate system. What type of themostat are you using brand and model? Boilers gas valve brand and model?
http://ashrae-meteo.info/v2.0/places.php?continent=North America

Thanks for your reply, I apologize for my late reply. When I supply the supply side I do get more bypass flow and a higher temperature mix of return and bypass, though I am not getting much warm water on the supply circuits, particularly the circuits in the upper floors.
The thermostat I am using is a Honeywell RTH6400 series. It is programmable though it is set in hold mode at constant temperature (20C).

 

[Jean-Sebastien Stoezel]

Without knowing the total size of the radiation it's hard to say if the boiler is undersized for the radiation (probably not), but for a 2400' residence the boiler is all but certainly OVER sized for the design heat load, even in colder parts of Manitoba. Is this an uninsulated double-wythe brick structure with only single-pane windows (no storm windows)?

Using fuel-use against local heating degree-day data it's possible to directly measure the design heat load of your house using this methodology. Odds are pretty good you have enough radiation to make optimal use of a right-sized condensing boiler, but alas the CGI series isn't one of those.

Thanks for the reply. The heat loss study from 2 different plumbing companies suggested that the house needed a net 100kBTU boiler. And so, when the old 210kBTU boiler died, the first boiler that was installed was in fact a CGI-5 with a rating of 119kBTU . This boiler could not maintain heat in the house and the CGI-6 was installed.
This house is a lumber frame with what appears to be 4" worth of saw dust in the walls, and pretty well packed up to the ceiling of each room. Most windows are now recent (less than 10 years) PVC type, double or triple pane with Argon. They are some original windows that are single pane with storm windows fitted. The basement was recently renovated with spray foam bringing the insulation to be over be code requirements. Some rooms in the house have been renovated, the studs have been extended to bring the walls to 6" deep, with R24 insulation.

While I understand that the house is not energy efficient, the return temperature should be able to be much more than what I am observing. Particularly these days when I am testing the system, running extended boiler runs (close to 90min), and in unusually warm weather conditions for this time of year. We have been sitting at -5C - today is actually -1C. This is a far cry from the -20C to -30C we should be going through right now.

 

[Fitter30]

Did you happen to program your thermostat heat cycle rate to 3?