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Baseboard Loops

Hello Everyone! Thanks in advance for your input ;)

I'm installing a totally new hot water baseboard system. I'm using a condensing combi boiler with 170,000 btu output at 91% efficiency, pex tubing, and hot water baseboard heaters. My baseboards put out 730 btu/ft at 180 degrees entering temperature.

This is my concern. I don't want to run loops that are too long such that they don't put out enough heat at the end of the loop. My living room requires 25 ft. of baseboard. I was hoping to take that into the den which requires about 10 ft. of baseboard. I know heating won't be 100% even doing it this way, but I want the den to be comfortable, even if slightly cooler than the living room. What's your thoughts guys?

I know this will save me A LOT in materials and labor. I have to open up the walls to install the pex tubing, and doing it this way keeps me from opening the walls in practically every room. Plus it cuts down on the cost of pex, which, though not expensive, every penny counts, you know?

Re: Baseboard Loops


Yes, according to the calculations I have you should be alright with up to 68' of baseboard in the living room/den, providing you're using 3/4" baseboard tubing.

1): Baseboard radiation USUALLY comes in 3/4" convector pipe sizing, but THERE IS some 1/2" pipe sizes on the market, in which case the limit would be 27' per convector length---check the sizing on your baseboard tubing just to be sure you have the needed 3/4" size.

Click onto the comfort-calc site below & scroll down to "Hot Water Boiler Info"----- follow the prompts to "maximum btu & max radiation per pipe size"----->"flow, max radiation & btu output"---->"max amount of copper baseboard allowed".

2): There are some other concerns that came to mind---standard 3/4" baseboard is rated at 560 btu output/linear ft.@ 180 degrees; though there is a high output version that emits 800 btu output/linear ft.@ 180 degrees---so check the output on the baseboard you have to be sure.

3): Have you done a HEAT LOSS CALCULATION of the living room & den to calculate how much heat you need in these rooms to make them feel warm in the Detroit area??? If you need a HLC, there are some below that will give you some idea of how much heat your LR & den are losing per hour on a cold day, & how many BTU/hr your baseboard will have to supply to make up the loss so you feel warm----it all depends on how much insulation you have in the exterior walls, how much glass (windows) you have in the LR/den (double-pane glass is just about a must) , your geographical location/how cold it gets in your location, etc.

4): 180 degrees is about the MAX any HW boiler puts out when it is operating on a cold day---you also have to consider ALL THE CIRCULATION of all the convectors in the rest of the house---the boiler has to circulate & heat all the convector water throughout the house, & is continualy being confronted with cold water coming in from the rest of the house baseboards that it has to heat----thus, it takes time & the temperature of the heating system water in the real world thus FLUCTUATES around 130-150 degrees & only gets to 180 degrees at the end of the 20-30 minute heating cycle as it is pumped thru all the house radiation----so it may take some time before the LR/den will heat up to a comfortable level---the LR is often the largest room in the house & is usually where the occupants spend most of their time----this becomes noticeable on cold days; the T-stat is thus usually best located in the LR for this reason.

My experience with baseboard, especially standard/hi output baseboard at the lengths you are installing, is that it doesn't have the lasting heat output of some of the other available convectors, which can be mixed with the baseboard if you run into trouble with insufficient heat in the LR/den-----namely adding a cast iron rad/stainless steel rad under a window in the LR; another characteristic of baseboard is that it gives off its heat, then COOLS OFF VERY QUICKLY, since it is made of thin materials of copper tubing/thin metal; on the other hand, even a small 4' cast iron rad gets hot & STAYS HOT for a 1/2 hour to an hour, long after the boiler stops pumping its hot water.

Another option, if the installed baseboard doesn't give you enough heat, is putting the LR/den on a SEPARATE ZONE using a ZONE VALVE (this would mean again opening the walls to install the dedicated piping, though) & having the LR/den on its own zone with its own T-stat, especially if you have a large LR with a lot of glass----but first see if the installed baseboard works for you----you can always go back at a later time to add more dedicated rads or a zone, if needed.

The first 2 HLCs are simple & are designed to give you a rough idea of how much heat you need for the LR/den; the 3rd HLC is much more comprehensive, takes long to load on your system, & is from Slant/Fin;---at the site, click onto "Slant Fin Heat Loss Calculator"


Re: Baseboard Loops

Thanks for the great info. I'll try out the Slant Fin HLC when I get home! I initially used the BTU requirement calculator at PexSupply.com

I would:

  • Select High Temperature
  • Enter the Square Footage of Each Room (Living Room = 567)
  • Select State (city automatically pops up)
  • Age of Home is "More than 50 years..."
  • No to Renovations

This gave me a BTU requirement of ~28k for a 567 sq ft room.

I then used the BGM Supply calculator with room dimensions: 24*24*8 with a Multiplier of 6. This gave me ~27.7 sq ft.

So I think I'm on track here!

On the baseboard issue your urging to look deeper led me to do so. On PexSupply's website they innacurately list BTU Output as 840-1030.

The actual BTU Output for these models is 490-1110. I initially calculated that I'd need 35' of baseboard for my 567 sqft LR at 840 btu/ft. These models use the 83A heating element which will put out 730 btu/ft @ 1GPM with 180 degree water. Recalculating my needs, I'll actually need 38' of baseboard.

The pipe is 3/4" so I should be fine on my runs.

In terms of layout I was planning on 1 zone per floor, each zone will have 2 loops. This will keep each loop to a relatively short length.

The boiler I plan to use is the Navien CH-210-NG. Its output is 170,000 btus @ 91% efficiency, yielding a tiny bit more output than I actually need. I spoke with the manufacturer some time ago because it maxes at 185 and I was concerned with running it so close to its max output temperature but they said that's what most installations do and they've been working fine so I'll give it a try.

Re: Baseboard Loops

Personally I would consider zoning rather tha looping. Yes it will cost more initially but will provide more satisfying heating and allow cutting down on rooms when not is use saving fuel.


Re: Baseboard Loops

I think what you're calling a zone, I'm calling a loop.

As I understand it, a zone is a separate heated area. A zone, can have multiple loops, each loop in a connected zone is heated (somewhat) equally.

My house has two upper levels and a basement. Each level will be its own zone. This means I could individually heat the basement, main living floor, or bedroom floor, or I could heat them all at the same time.

Each zone could have as many or as few loops as necessary. So take the 2nd floor of the home. I have 4 beds and 2 baths. Ideally, each room would have its very own loop to ensure even heating. So thats 6 loops on zone 3.

My main living level has LR, DR, Kitchen, Half Bath, Den, Foyer, and 2 hallways. If each room had its own loop, that would be 8 loops on zone 2.

My basement has another kitchen, living room, den, laundry room, half bath, storage room. If each room had its own loop that would be 6 loops on zone 1.

The purpose of a loop is (1) to keep heating elements under the required maximum length and (2) to distribute heat evenly. As hot water travels along a baseboard it loses heat, anecdotally, we would observe that the end of a baseboard run is slightly cooler than the beginning. The longer the distance between the start and finish of a run, the cooler it will be.

This causes uneven heat distribution wherein rooms at the end of a heating loop are much cooler than the one at the beginning.

Lets assume for a moment that I have no individual loops, that each level is its own zone.

If I had the hot water start in my room and finish in the baby's room (farthest from my BR) then his room would be cooler. To get his room warm, I'd have to turn up the heat which would make my room unbearably hot.

To remediate this problem you create different loops. Each loop makes it possible that the entering temperature in every room is even. It is IDEAL to have each room on its own loop, and have rooms grouped into categories by usage (typically by level, but in larger homes this may not always be true). That way each room starts off with 180 degree water, and they're all heated evenly, and should have just about identical temperatures. But in my installation I'm doing a complete retrofit. So that wouldn't be practical because I'd be tearing up so much of the house. So I've settled for 2 loops per zone instead of those listed above.

Re: Baseboard Loops

I agree with JL McDaniel.

The heat loss calculations attempt to consider all the variables such as exposed walls, amount of insulation, total square footage of window glass, etc., but as Dobbs points out, they often ignore real-life conditions such as actual temp of the HW running thru the convectors, and assume that so many gallons per minute are being pumped thru the convectors, when in reality there may be a small circulator pump driving the system that's pumping only 25% of assumed gallons per minute.

Always have at least one or two experienced local heating techs check your calculations---they will point out things that you may have missed in your HLC calculations, and you'll end up with a better install.

They also have an excellent free consultation service at Slant Fin and the other mfgrs of Baseboard and PEX tubing if you call their 800 number.

Giving the fact that the LR is so large, I concur with McDaniel's suggestion that it should be put on a separate zone with its own T-stat.; that way, even if the final HLCs are off, you will still have climate control of the one room you'll be spending a lot of time in.

We just want you to finish this project with the best results possible.

Re: Baseboard Loops

Personally, I would like each room on a separate zone. That way you can control the heat in heat and lower the temp in unused rooms.


Re: Baseboard Loops

I agree, it is ideal that each room start with the same temperature water. But that would just be too expensive an install for me. I will be using distribution manifolds so I could cut heat to a section of the house at a time, but not by individual rooms. With my planned layout, I could cut the heat to the kids room and save some money on that when they move out! ;)

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