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Added room is too cold... new baseboard or panel radiators?

DJDrewDJDrew Member Posts: 45

Over the years we have been slowly improving the performance of our hot water heating system, thanks to much advice obtained here. We have two other issues that still need addressed and the family is asking that I focus in on one of those before winter arrives.

The environment:
We have a small 70's addition to our 1938 house, it is only 5x7, but contains a door and two windows. It is divided into two parts, a heavily used entry/exit and a bathroom. The whole area sticks out from the house and is over a crawl space. When the area was built out, those that be installed cast iron baseboard; a 2 foot section in the entry and a 2 foot section in the bathroom. The rest of the house has oversized CI radiators. The boiler usually only heats the system up to about 130 degrees until the stats are satisfied. On 5 degree design days last year I noticed the water temp getting up to ~137 degrees. The boiler is a two year old Slant/Fin and the run times are 35-60 minutes at a time, so there is no short cycling.

The problem:
The bathroom and entry, as described above, are significantly colder than the rest of the house, and being somewhat isolated, don't get much natural airflow from the rest of the house. Fixing an electrical issue 2 years ago, we spray foamed the rafters in the ceiling and stuffed the walls of insulation. I hope to insulate the crawlspace in the future, but I think the sill of this addition was never sealed right, and until we put new siding on the house, that won't get fixed.

Slant/FIn's Heat Loss calculator is telling me that, even after insulating, I still need ~2300btu/hr for the space. The current cast iron baseboard, operating at 130-140 degrees, is only putting out a total ~1360btu/hr according to the specs I can find online.

I had two quotes for possible work to correct this, and I was wondering if anyone had some thoughts.

Quote 1: Install High-Output Slant/Fin Baseboard. The Multi-Pak 93 with the H-1 3/4" element, total of 5 1/2 feet of length in the two areas (3 feet in the bathroom where there is more room and 2 1/2 feet in the hallway.) They estimate this would put out 2100-2300 btu/hr.

Quote 2: Install two small panel radiators, one in the entry and one in the bath. The Buderus Model 21, 12" x 24" (970btu) for the bath and the entry would get a Buderus Model 21, 20" x 24" (~1400btu) . The estimated output total for the area was is ~2300btu/hr.

I have heard it is not a good idea to mix baseboard and cast iron radiators, but the installers for quote 1 said that because I have long run times on the boiler it would be okay. Would anyone have any thoughts or suggestions?



  • JohnNYJohnNY Member Posts: 2,372
    You need more energy. It sounds to me like your boiler is too small for the home hence the low water temperatures and long run times. Adding more heating elements with higher output may aid in make the rooms warmer but they'll definitely make the return water cooler, which seems to be a problem right now...unless you're using a high efficiency boiler which is designed to withstand cooler water temperatures which is a condition that develops a corrosive condensation and is not a sustainable thing for standard boilers. Do you know the model number of your boiler? Pictures always help.
    For installations, troubleshooting, and private consulting services, find John "JohnNY" Cataneo here at :
    "72°F Mechanical, LLC"
    Or email John at [email protected]
    John is the Boilers and Hydronic Heating Systems Course Instructor at NYC's Mechanics Institute, a professional Master Plumber, licensed by The Department of Buildings of The City of New York, and works extensively in NYC while consulting for clients in and out of state.
    John also oversees mechanical installations and maintenance for metro-area clients with his family's company, Gateway Plumbing and Heating along with his brother/business partner.
  • Solid_Fuel_ManSolid_Fuel_Man Member Posts: 1,758
    Your boiler may not necessarily be too small, its likely that you have an old gravity system with many many many gallons of water, which is good!

    Mixing radiation types, is really for the different associated heat outputs at given water temps. If it's all sized according to the same water temp then you are fine!

    Ive used cast rads and radiant slab all at the same water temp without issues, the rads were technically grossly oversized to the heat loss, but at low water temps (slab) they were sized correctly.

    I'd go with whichever you like the looks of the best. If both quotes are sized for as much heat that you need at typical operating temps then you are good.

    Can you change the piping so that the addition radiation gets water first? Or is a different zone?

    A mod/con would work well at those low water temps.
    Serving Northern Maine HVAC, and Controls
  • DJDrewDJDrew Member Posts: 45
    edited August 13
    Hey @JohnNY ...the boiler is a Slant/Fin SE105. The heat loss calc for the whole house totals 70,545 when I am using basic insulation. When I put the numbers in with the house fully insulated the way we want I get ~48000 btu/hr. We have been slowly updating the insulation as we work on various parts of the house. Last winter we managed to finally insulate and air seal the attic, so I suspect our boiler is sized correctly.

    Last year we also added boiler protection after I noticed the return temperatures were fairly low. This is the thread that goes into depth about the install and return temperatures of this system.

    Overall the house is comfortable, aside from this one area. We have some flow issues getting to the radiators farthest away (causing them to heat last and thus the heat being uneven or minimal in those area) but in general everything works well. When I went through and calculated the radiators in each room, the oversized rads accommodate the amount of btus needed with lower water temp.

    Increasing the flow to the further radiators is the only other issue we have with the system, but I was told by both installers to fix the undersized heat delivery in the bathroom and entry first since it is more noticeable. The entry and bathroom are located more centrally and as such the cast iron baseboard heats up fairly quickly when the system is running.
  • DJDrewDJDrew Member Posts: 45
    edited August 13
    @Solid_Fuel_Man Thanks, yes I am double checking everyone's numbers to make sure the btu output will work at the lower water temperatures.

    Currently the cast iron baseboard is fed off of supply & return 1-1/4" Iron pipe that runs like a freeway around the perimeter of the basement. It is tapped of the large supply/returns to 3/4" copper, pipe insulated, and then run through the crawl space and up. Currently the cast iron baseboard seems to heat up fairly consistently with the rest of the system.

    I do think the there are flow issues in this area of the house, but there seem to be some further down the lines.

  • Solid_Fuel_ManSolid_Fuel_Man Member Posts: 1,758
    So is it a direct return or reverse return system? Can you draw out the piping?
    Serving Northern Maine HVAC, and Controls
  • DJDrewDJDrew Member Posts: 45
    edited August 13

    So is it a direct return or reverse return system? Can you draw out the piping?

    Certainly. I think it is a direct return. Every radiator is piped directly to a supply and return.

    Attached is a drawing of the pipe layout. I numbered each radiator. 2Rad is a second floor rad, 3Rad is a 3rd floor rad. The ones that are circled are the ones with the slowest flow/heat up only at the end of the call for heat.

    The boiler pump is a Taco 007. The main supply lines are 1-1/4" aside from the very end of each run, right before the last 2 radiators are connected it switches to 1" mains.

    3/4 radiator supply and return piping to Rad2 and the cast iron baseboard. The rest of the individual supply and returns are 1/2".

  • Solid_Fuel_ManSolid_Fuel_Man Member Posts: 1,758
    edited August 14
    Do you have a finished basement? If all of the supply and return piping is 1-1/4, you can make that a reverse return, and most likely cure all of your low heat woes. It certainly makes sense that both ends would have low heat output. Your addition is doubly bad as it's on and end and has a longer horizontal branch.

    Also you may have good results from switching to a 0010 circulator. It's a high velocity low head pump which would lend itself to the unbalanced flow. Fitted to pump away from the expansion tank. But, reverse return would work the best, but require the most repiping. Or go to a homerun system with 1/2 pex and demo all the large iron pipe.
    Serving Northern Maine HVAC, and Controls
  • DJDrewDJDrew Member Posts: 45
    Thank you @Solid_Fuel_Man - most helpful. I looked up some ideas for a reverse return, certainly seems possible, especially since we only have a partially finished basement. I'll have to get some quotes on making that change.

    I also like the idea of pex, but that seems like even a bigger job, but would let me balance every radiator and gain some headroom.

    Thank you for the suggestions, and the thoughts on the added btu heating panels!
  • Big Ed_4Big Ed_4 Member Posts: 1,140
    Every floor or addition should be seperately zoned ..
    I have enough experience to know , that I dont know it all
  • DJDrewDJDrew Member Posts: 45
    edited September 18
    So I was looking up some of the suggestions for fixing the low-flow to the end radiators since the system would be drained for installing the new panel radiators.

    I remembered a few people saying a Primary/Secondary with T's would also likely help with the low flow at the end of the lines... would this be easier compared to the work of creating a reverse return setup? It seems that a Primary/Secondary setup would keep most of the work contained to the mechanical room.

    @hot_rod shared a slide with me last year showing Primary/Secondary options. I circled the one that I think would be most simple since there is already a thermostatic valve installed for boiler protection. I could then look at getting the 0010 pump for the distribution loop. The only modification is removing the second thermostatic valve, since I'm not concerned with a high temperature flowing to the radiators.

    Think that would be acceptable and reasonable to modify while the system is drained anyway?

  • bob eckbob eck Member Posts: 893
    Check out these steel panel wall radiators.

    Check out Heating Edge HE2 copper baseboard. It’s maybe to be used on low water temp systems.

    Is there room to put a vertical wall panel radiator in? There are wall panel radiators made that are 4’ or 5’ long that can be mounted on the wall and go vertical with it. Check out look at their Narbonne vertical and horizontal radiators
    Their Ecostyle steel wall panel radiators are great and competitive priced.
  • DJDrewDJDrew Member Posts: 45
    bob eck said:

    Check out these steel panel wall radiators.

    Check out Heating Edge HE2 copper baseboard. It’s maybe to be used on low water temp systems.

    Their Ecostyle steel wall panel radiators are great and competitive priced.

    Thank you Bob! I was unaware of those, this gives us some good options. My wife likes options.

  • BrewbeerBrewbeer Member Posts: 593
    Sterling Baseboard also makes a few models that have good low temp output, the Heat Trim Plus line was installed in my system which runs at about the same temps yours does, @DJDrew but baseboard can be dicey in a bathroom.

    I'm not sure anyone mentioned the idea of constant circulation in the system or perhaps in just those radiators that need it. If you had a reservoir of stored heat (like a tank, and/or the other big radiators?) and constantly pump it into the two cold room radiators, that could help.
    Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread:
    System Photo:
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