Heating help - hydronic system

miguelmojica

Hello all. I'm trying to understand how the hydronic heating system works exactly, so I can determine what the issue is with the system the home I bought has. More specifically, how does having more BTU translates to more heat if the boiler can keep the supply setpoint.

What I understand is that there is a water boiler heating up water to a set temperature. This water is pushed through baseboards or radiators to heat a room. The hot water running through the baseboard gets colder as it irradiates heat, and returns back to the boiler to be warmed up again and repeat the process. The boiler produces energy measured in BTUs, and the baseboards deliver the BTUs.

I got a natural gas Peerless PureFire PF-80 water boiler in Central Heat mode only (No DHW), to heat a 2160 sqft home. It's pushing hot water through regular fin baseboards. There are 2 zones controlled by zone valves. 2 taco 007 circulators at supply and return points. No outdoor reset. Operation mode is permanent demand. 

The issue is that whenever the outside temp is below 20 degrees F, the boiler cannot keep the target temp of 72. I could jump to the conclusion that it's undersized, but it can mantain a setpoint of 180 and even 190. Wouldn't that mean it should be able to take on the heating load? The boiler is rated for 80k BTU. How can I determine if it's the boiler not producing enought BTUs, or the baseboards not being able to output the BTUs needed for the space?

-Boiler Setpoint: The setpoint is 160 by default on this boiler. I have set it to 180, and even 190 to test, but that doesn't help much (setpoint = temp - 160=65, 180=67, 190=68/69 @ 10°F). Return is between 10-15 degrees colder.
-Insulation: The house was built in 1978, so it's got basic insulation. The windows aren't the best. I put a plastic shield on all of them to help with drafts and keeping the heat in. Other than this, I don't know what my heat loss is.
-Baseboard footage: There seems to be adequate baseboard running in each room to heat the home. I doubt it's the baseboards because one of the smaller rooms has way too much baseboard, and it's only slightly warmer than the rest, by maybe 1 degree. With that said, I don't know enough for my opinion to matter .
-Air in system: I flushed each zone after I first noticed the problem to make sure there wasn't air bubbles. The is also an air eliminator vent above the expansion tank.

If you've made it this far, I greatly appreciate your time and willingness to help. I've called two plumbers already and they don't work with the kind of boiler I got, which I find strange... at least they were honest upfront about not knowing instead of BS their way through. I want to fully understand the issue variables and potential resolutions so I can catch any BS for when I call the next plumber.

skiereric

A couple of things.
BTU vs BTU/hr.
The output of a heat emitter (panel radiator, baseboard, etc) is measured in BTU/hr. The amount of heat a boiler produces is also measured in BTU/hr (BTUH)
The proper heat emitter for each room is determined by a heat loss calculation.

The amount of heat that is lost is greater than what your heat emitter can give off. Therefore the room loses heat. If it is equal (perfect situation) no heat is lost (temperature is flat) if the amount of heat generated is > than the heat that is lost, the temperature of the room will increase.

From what it sounds like - the heat emitters are undersized based on the heat loss of the space.

Also, be careful with the set point - it should be based on the heat emitter.

Aluvaboy

I also recommend to check the circulator pump and the zone valves. How old are they? Maybe the impeller is all chewed up and the zone valves do not open and close completely. Although it might appear to be working, hot water is probably not circulating well. Also check to see if there is air in the system. It recently happened to me after I changed the zone valves in my system. One zone would not get hot. After I purged the system, it started working again. Circulator pumps are not very expensive. Around $150.00.

EdTheHeaterMan

@miguelmojica. You have a great explanation of your issue.  I think you understand more than you think you know. There is a booklet I used for teaching a seminar on Hydronics that may help

https://documentlibrary.xylemappliedwater.com/wp-content/blogs.dir/22/files/2020/01/FH-Z100B-BG-Zoning-Made-Easy-2.pdf

The purpose of the 2 circulators may be a little different than you think. I believe you have discovered your issue.   The system needs a higher temperature as the outside temperature drops    When it is below 20°F outdoors the boiler temperature needs to be 190°F. When it is below 10°F you need 200°F in the boiler.  If the temperature ever reaches 0°F then you may need 210°F in the boiler.

Setting the limit temperature to 210° for the entire year would be wasteful. An outdoor reset control would benefit you in this situation.   In order to maintain a reasonable limit temperature for most of the year then, only when the temperature reached the extremes below 20°F, would the boiler temperature be allowed to increase above the 180°F that you would normally use. 

EdTheHeaterMan

another thought came to mind after I posted the information above. I remember one customer that would call me every other year or so. They were complaining of insufficient heat similar to your situation. The only time they would call me is when the outdoor temperature was below 12°F. Since this did not happen every year, I did not get the call every year. However when I did get the call I checked the system and found that it was operating normally. Then I looked at the baseboard emitters  and I noticed that a shag carpet  was installed and blocked the airflow under the baseboard radiators. Since 80% of the BTU capacity of a baseboard radiator is convection air current flowing through the enclosure, And the airflow was restricted by the shag carpet, The radiators were not able to keep up with the heat loss of the room. 

Check that your heat emitters are free and clear of anything that may restrict airflow.  There may be lint or dust on the underside of the elements.

BTW After the third time I gave the same answer to the customer (over a 6 year period) I told them they needed new baseboards and offered a Ridiculous price to fix the problem.  They called me again a few years later and I remembered them this time (With the help of new software to track customer history) and asked them if they wanted to get the new radiators or just pay for a service call to tell them they needed new radiators.  They declined the service call, saving them money and me a special trip to tell them what they already knew during my busy schedule 

wmgeorge

Has it been working fine until.....? Or never? Replacing your windows will be like magic on your heating loss 20-30% and re-insulate the walls. Otherwise do a room by room heat loss calculation. There are some folks here can help with that. If something has changed go that route. Ed has posted some great info.

miguelmojica

skiereric said:

A couple of things. BTU vs BTU/hr. The output of a heat emitter (panel radiator, baseboard, etc) is measured in BTU/hr. The amount of heat a boiler produces is also measured in BTU/hr (BTUH) The proper heat emitter for each room is determined by a heat loss calculation. The amount of heat that is lost is greater than what your heat emitter can give off. Therefore the room loses heat. If it is equal (perfect situation) no heat is lost (temperature is flat) if the amount of heat generated is > than the heat that is lost, the temperature of the room will increase. From what it sounds like - the heat emitters are undersized based on the heat loss of the space. Also, be careful with the set point - it should be based on the heat emitter.

Thank you for your reply. I'll try to calculate the heat loss. Assuming the emiters are sized correctly, what would be the symptom that determines the boiler is undersized? Something like the boiler not being able to keep up with the setpoint temp? Just out of curiosity. 

miguelmojica

Aluvaboy said:

I also recommend to check the circulator pump and the zone valves. How old are they? Maybe the impeller is all chewed up and the zone valves do not open and close completely. Although it might appear to be working, hot water is probably not circulating well. Also check to see if there is air in the system. It recently happened to me after I changed the zone valves in my system. One zone would not get hot. After I purged the system, it started working again. Circulator pumps are not very expensive. Around $150.00.

Thank you for your reply. Not sure how old they are. I just bought the house 2 months ago. I opened the zone valves manually and left them opened to test this theory once. It didn't help. The circulators seem to be working, but I haven't taken them apart to see if they are clean. I flushed the lines to rule out air bubbles too.

miguelmojica

EdTheHeaterMan said:

another thought came to mind after I posted the information above. I remember one customer that would call me every other year or so. They were complaining of insufficient heat similar to your situation. The only time they would call me is when the outdoor temperature was below 12°F. Since this did not happen every year, I did not get the call every year. However when I did get the call I checked the system and found that it was operating normally. Then I looked at the baseboard emitters  and I noticed that a shag carpet  was installed and blocked the airflow under the baseboard radiators. Since 80% of the BTU capacity of a baseboard radiator is convection air current flowing through the enclosure, And the airflow was restricted by the shag carpet, The radiators were not able to keep up with the heat loss of the room. 

Check that your heat emitters are free and clear of anything that may restrict airflow.  There may be lint or dust on the underside of the elements.

BTW After the third time I gave the same answer to the customer (over a 6 year period) I told them they needed new baseboards and offered a Ridiculous price to fix the problem.  They called me again a few years later and I remembered them this time (With the help of new software to track customer history) and asked them if they wanted to get the new radiators or just pay for a service call to tell them they needed new radiators.  They declined the service call, saving them money and me a special trip to tell them what they already knew during my busy schedule 

Thank you for both of your replies. They were vedy insightful and helpful. I'll check that the baseboards are clean and remove the plastic cover they got on for a few days to see if that helps the airflow. What made you determine it was the baseboards and not the boiler? I would much rather replace the baseboards in the bedrooms than a boiler lol. 

ratio

Also note that it's the length of the heat emitter inside the baseboard that matters. The baseboard could be 40' long, but if the finned section of pipe inside is only 10' long, well, that's the length of it.

Clean the baseboards, check for obstructions, after that it's time to check sizing. Slant/Fin has an app you can use to cypher up a relatively-accurate heat loss. It goes room by room, & coincidentally will give you suggestions for the necessary Slant/Fin baseboard & boilers.

miguelmojica

wmgeorge said:

Has it been working fine until.....? Or never? Replacing your windows will be like magic on your heating loss 20-30% and re-insulate the walls. Otherwise do a room by room heat loss calculation. There are some folks here can help with that. If something has changed go that route. Ed has posted some great info.

Thanks for your reply. I just got the house, so I don't know if it ever worked correctly. But it's been like this since we moved in so, I guess? I'll certainly replace the windows before the next winter. If money stretches enough, I'll insulate the roof sheathing in the attic too.

Zman

How is your boiler piped? Pictures would help.

miguelmojica

Update on this issue: it was the heating element. I replaced the heating element in 2 of 3 bedrooms. Last week when temps dipped under 20°F, the 2 beedrooms kept a temp of 70-71, while the 3rd bd was 65-66. Thermostat was set to 72°F. Boiler setpoint was set at just 150°F, compared to 180-190 last year. I installed the H-3 heating element with the multipak 80 housing from slant/fin, for reference. Now I just have to replace the baseboard in the rest of the bedrooms and areas where I want heat to keep up. Thanks to all who took the time to look into this and helped out! Special thanks to @EdTheHeaterMan. You were spot on buddy.