Cast iron baseboard heating unevenly

[Linds]

Hello!

Our house, built in the 50s, is heated with a boiler and cast iron baseboards(pretty sure both are original). We have 3 zones. The zone with the bedrooms is the problem area as it runs through 3 bedrooms and a bathroom and heats the rooms unevenly.

The master (number 1 in the photo) has the longest baseboard(red in the picture), is first in the hot water loop, and has the zone's thermostat in it.

Number 2 is a smaller bedroom, 3 is the long, skinny bathroom, and 4 is the smallest. Room 4 is by far the coldest since it's last in the circuit and has the smallest amount of baseboard out of the 3 bedrooms.

The problem is that room 1 gets heated very quickly, so the thermostat measures the target temp and shuts off. It is on for such a short time that the other rooms' baseboards receive hardly any heat. They only get piping hot when the temperature delta is much larger so the system runs for a longer period of time.

This all makes sense but we have kids in the smaller rooms who need more heat than we do. Yes, we could do space heaters, but is there something we should do to try to fix this? We've tried bleeding air to no avail. Just tried switching the thermostat to a nest to see if it changes anything. We've turned the water pressure up on the boiler. Should we insulate bedroom 1's baseboards so the hot water reaches the other rooms? Adjust pressure/temp? I should add that the system runs for such a short time that the boiler doesn't even reach the target temperature.

Picture of the system and baseboard included

Thank you!

 

[Sylvan]

I hate loop systems for this very reason

 

[Sponsor]

 

[Mage182]

What are the specs on your boiler?

 

[Dana]

This sort of thing happens when...

A: the water temperature is too high

...and/or ...

B: the flow rate is too low.

The flow rate can be low for several reasons, such as air in the system, clogged filters, partially closed valves, failing pump impellers, etc.

A high water temperature combined with low flow means that as soon as the baseboard rads begin to get hot the thermostat is satisfied quickly, with only the first in the series getting warm, since that's where the thermostat is located. Backing off the temperature reduces the heat emittance rate in the first room, and allows warmer water to reach the rest. Using an "outdoor reset" approach to water temperatures, where the water temperature automatically adjusts up/down in response to outdoor temperatures can usually fix this, even with fairly (intentionally) low-flow systems. But before diving in on how to fix it in your system more information is needed on the boiler, boiler settings & pumping configuration, etc.

That looks like the ( no longer available ) 6" tall version of Weil-McLain Snug baseboard, which is pretty nice stuff when the system water temperatures & pumping are optimized. It's very comparable in every respect to Burnham's 7A Base-Ray (including output across flow & temperature.)

So, how many running feet of 6" Snug do you have on that zone?

 

[Dana]

BTW: A boiler that was installed during the Truman or Eisenhower administrations is well beyond a normal service life, and unlikely to be delivering it's original ~80% combustion efficiency. Most boilers of the era were also 2-3x oversized for the actual design loads of the house even before any upgrades to air sealing, insulation or windows that may have happened over the past 60 years. While it still heats the house just fine, the age & oversizing factors impact negatively on efficiency. If you're planning to live there for another handful of years or more it's worth at least considering a right-sized higher efficiency replacement.

If the boiler's high limit is set to 180- 200F or more, back it off to 160F, see if the comfort levels improve. Like the boiler itself, the overall radiation sizing is likely to be 2x oversized, which means you can probably still heat the house with 140F water or cooler water, but dropping the temp too much could create excessive condensation issues inside the ancient cast iron boiler.

 

[Linds]

Thank you for all the replies. I am attaching several pictures for the specs since I wasn't sure what to give you. Let me know if it's missing something. The pump for this zone was replaced in 2011 and is the newest one compared to the other 3 zones, so I don't think it's a pump flow rate issue. Although the air in the line is very possible...
One interesting thing that I can't figure out. When I tried purging the baseboards out of air, the first 3 rooms acted an expected, with water coming out, meaning there was no trapped air. However, the last room nothing comes out when I open the Purge valve. There is no air coming out either which makes me think something may be clogging it? I can show a picture of the valve if needed.
Thanks for all the help.
Btw the picture of the psi and temp gauge is when the system is idling or not heating any zone.

 

[Mage182]

I use the same baseboard to heat my whole house. One zone on each floor. Dana's comments about flow and temp are spot on as usual. I also used thermostat positioning to control my situation. Having the thermostat in room 1 is always going to yield the shortest run times. Can you move it so that it's in the hall outside the rooms? When I moved mine there the heat evened out noticeably as long as the doors are open. At night with the door to my room 1 closed it still gets a little warm in there.

 

[Dana]

With a DOE output of 153,600 BTU/hr that sucker could heat my 1920s house with 2400' of above grade conditions space + 1600' of insulated below-grade basement to 68F indoors at an outdoor temp of -200F (if the natural gas wouldn't be condensing into a liquid in the meter, that is.) Don't know how big your house is or how much baseboard you have, but it's unlikely that your design load is even 50,000 BTU/hr, or that your baseboard could emit that much.

Measure up how many feet of baseboard (or other radiation) you have on the three zones, zone by zone. It's an important consideration for determining how to set up the boiler's temperature and overall system.

Also, with last winter's gas bills run a fuel-use based whole-house load calculation (wintertime fuel use only), using EXACT meter reading dates and amounts. The whole house load and baseboard lengths makes it possible to ballpark the minimum water temperature needed to heat the place adequately.

With the high-limit set to ~173F there is still room to turn it down without creating condensing issues inside the boiler. Back it off to 160F, which will knock about 20-25% off the heat emittance of the baseboard, increasing the amount of time it takes for the thermostat to be satisfied.

Is the air purge valve on the other baseboard on of the small needle-valve types?

Those are cheap and replaceable (box stores carry them in my area), but it could be clogged with rust bits. Sometimes backing the needle valve out entirely to purge air/water can clear the clog. Only try that when the system and radiator is cold.

In the picture with the pumps there appears to be what may be adjustable flow balancing valves about 8" above the pumps. Have you tried tweaking that? Are there any other in-line valves on that loop?

 

[Sylvan]

It would help a lot if you also insulated the exposed piping

 

[Fitter30]

Theres at least three pumps and one thermostat. What happens whens the thermostat calls for heat and what turns the other pumps on?

 

[Dana]

Y'all realize that this post went idle about 50-51 weeks ago, right?