Heating baseboard (C) Carson Dunlop Associates Guide to Baseboard Heat
Heating Baseboard Inspect, Repair, Cleaning

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Hot water baseboard heating systems:

This article describes the types of baseboard heat used in buildings and we explain the diagnosis and repair of heating baseboard troubles including no-heat or leaks or other problems. This article focuses on the installation, diagnosis & repair of hot water heating baseboards.

We discuss: How to inspect, diagnose, and repair problems with baseboard heat. Inadequate linear feet of hot water baseboard: factors that determine how much baseboard is required. If your hot water baseboard is cold and the heating system is "on" - here we diagnose the problem.

Where leaks occur on hot water baseboards; Guide to unusual heating baseboards in buildings. How to raise up heating baseboard that lacks adequate clearance from the finish floor surface.

This article series answers most questions about all types of heating systems and gives important inspection, safety, and repair advice.

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Baseboard Heat: How to Identify and Diagnose Problems With Hot Water or Electric Heating Baseboards

Heating baseboard (C) Daniel FriedmanHow Does Heating Baseboard Work?

Hot water heating baseboard is warmed by hot water circulating through either finned copper tubing or through cast iron baseboard sections.

Our photo of a heating baseboard at left and also Carson Dunlop's sketch (below left) and oshow a typical modern hot water heating baseboard system installation.

Heating baseboard warms the room by a combination of radiation (the hot baseboard radiates heat onto surfaces in the room) and convection (cool air enters at the baseboard bottom, is warmed, and exits at the baseboard top - see Carson Dunlop's baseboard sketch at the top of this page).

[Click to enlarge any image]

If your heating baseboards are not in fact getting warm when your thermostat is calling for heat and the boiler is indeed running,

How Does Cast Iron Heating Baseboard Work?

Cast iron baseboard (C) Carson Dunlop Associates

Carson Dunlop Associate's sketch of cast iron heating baseboard shows the heating water and air flow pathways of these heating units.

You can see by the larger water volume as well as the increased mass of the cast iron, that cast iron heating baseboards have more thermal mass than conventional finned-tube baseboard.

The increased thermal mass means more even heat distribution as the baseboards will continue to radiate heat for some time even when hot water stops circulating through the system.

Sketch of a cast iron heating baseboard courtesy of Carson Dunlop Associates.

How Many Feet of Baseboard Heaters do We Need to Heat a Room?

The answer is ... it depends. Electric heating baseboard is figured at five to eight watts per square foot of the room. And for hot water heat, running a heat loss model such as the excellent program provided by Slant Fin™ can give a good estimate of the number of linear feet of heating baseboard will be needed for a given room or building area. But the following variables make an enormous difference in the answer:

Guide to Diagnosing & Fixing Cold Heating Baseboards

Heating baseboard testing (C) Daniel FriedmanCold Heating Baseboard Diagnostic Guide: how to diagnose a heating baseboard section, loop, zone, or room that is not receiving heat.

Make sure that your room thermostat is set to a temperature higher than the temperature in the room - so that it is calling for heat.

Make sure that your heating boiler is working, that is that the heating boiler turns on and off normally.

A hot water heating boiler may not turn on immediately when you turn up the room thermostat: if the water temperature in the boiler is already above the aquastat's cut-in temperature the circulators will send hot water to the radiator and the boiler will turn on later when its temperature is dropped by returning water from the cooler radiators in the building.

If your heat is provided by baseboards there will not normally be individual shutoff valves at those devices, but if your system uses one circulator and provides multiple heating zones (and thermostats) there will be zone control valves (usually near the boiler) that are opened or closed by the room thermostat(s).

Air-Bound Baseboard Heating Zone Diagnosis

Once your thermostat is calling for heat and the heating boiler has been running for ten minutes or more, just feel the baseboard. Don't cut your fingers on the fins, and don't bend them if you can help it.

If some sections of baseboard are not easy to access that's ok - you can simply feel the start and the end of a section of baseboard to determine where the loop of heat piping is hot and where along the system the baseboard piping first feels cold.

Our photo (left) shows an older finned copper tubing baseboard system with the end-cover removed - it's easy to just touch the copper pipe to feel its temperature - hot or cold, that's all we need to know.

If just some sections of an individual zone or loop of heating baseboard are not getting hot, feel along the piping entering and leaving each section of baseboard in each room to find which sections are hot and which are cold - this is a first diagnostic step in determining what's wrong.

If your heat is distributed entirely through one zone (one thermostat, one loop of heating piping & baseboards) and if part of that loop is warm (usually just the beginning portion of the loop), then there is a good chance that your heating zone or loop is air-bound.

We provide detailed, step by step procedures for diagnosing and curing an air-bound hot water heating system, beginning

Also see heating baseboard air bleed valves discussed
at AIR BLEEDER VALVES for more details.

Since on many hot water heating systems a key air bleeding or air vent point is at the air scoop or air separator closer to the boiler,

Thermostat, Zone Valve, or Circulator Pump No-heat Diagnosis for Baseboard Heat

If your heating system is divided into multiple zones of baseboards or a mix of baseboards and radiators: If the heating boiler is running and some baseboard sections or rooms are hot but others are not, first check to see if your heating system uses multiple thermostats and multiple heating zones.

It may be that the thermostat controlling the "cold" rooms is not calling for heat or is not working.

It could also be that the circulator (see Circulator Pumps & Relays)

or zone valve (see ZONE VALVES, HEATING) controlling flow of hot water to that heating zone is not working.

If your heating baseboard is installed over a carpeted floor, be sure that the carpeting has not blocked the air inflow space under the bottom edge of the metal baseboard cover. Blocking this air intake will drastically reduce the heat output from your heating baseboards, thus increasing your heating bill.

Heating Baseboard Defects

Missing baseboard end cover (C) D Friedman

Missing baseboard end cover (C) D Friedman Dirt dust clogged heating baseboard (C) D Friedman

Heating baseboard installation (C) D Friedman

Tepid or Cold Baseboards: How to Fix a Baseboard that Does Not Get Hot - Quick Advice

Make sure that your room thermostat is set to a temperature higher than the temperature in the room - so that it is calling for heat.

Make sure that your heating boiler is working, that is that the heating boiler turns on and off normally. A hot water heating boiler may not turn on immediately when you turn up the room thermostat: if the water temperature in the boiler is already above the aquastat's cut-in temperature the circulators will send hot water to the radiator and the boiler will turn on later when its temperature is dropped by returning water from the cooler radiators in the building.

Complete details about diagnosing and fixing cold radiators are found

Reader Question about a Cold Baseboard Heat Room on a Single Zone - do I need to replace the aquastat?

2/13/2014 Question - Honeywell Aquastat Control Replacement  said:

Hi Just wondering if I'm about to get ripped off or should i tell this person not to do the work. I have a 1800 sq foot 2 story house and the farthest bedroom on first floor (2 outside walls) away from the furnace in the basement (consistently freezing cold outside) has been much colder than the rest of the house (tenants keep heat at 75 and this room hovers around 64-68) It's a gas furnace - He told me its a Peerless Boiler and he is factory authorized dealer and the date on the boiler is May 2012. I have hot water radiator heat.

This new heating guy says the one year old Aquastat Control needs to be replaced - that it is a part failure unrelated to the workmanship of the previous contractor who did the work last year (i switched from Oil to Gas). That if he repalces the control that there is a 70% chance that this will solve the coldness problem in the back bedroom will get warm. If the whole rest of the house has been warm without any problem - is this really the problem, wouldn't the rest of the house be cold too? He wants to charge me $535 for the control 4 hours of labor at $65 an hour.

Now - its 2 days later, the room is still cold and now he's saying the baseboard heaters were installed wrong and need to be 'reworked' for $450. That they are upside down and this is why the room isn't warm (same original contractor who put in the new furnace put in these baseboards in last year). I called the original contractor (wish i brought him over this time to begin with) but I'm working with a property manager now).

He says that what this guy is saying is not true - that they were put in correctly. It was me who decided to use a 4' shorter length on one of the walls and this could be the issue, but why then did this new guy have to replace the control for $795. Do they really cost $535 or is that way high? Thank you for any help or advice anyone can provide. -Paula


Heating baseboards, typcial installation (C) Daniel Friedman

Really? I can't make sense out of the explanation given by your service tech. The aquastat turns the boiler on and off, and may control one circulator. I can't see how it knows one room of the home from another. The tech may be honest but a lousy communicator, but from just the information in your note, I don't get it.

In the article above you'll see more photos of normal baseboard installations. I've never seen heating baseboard installed upside down - I wouldn't even know how to do that.

At left I have inserted a photograph of a normal hot water heating baseboard installation with the baseboards "right side up" and with decent clearance between the baseboard bottom and the floor surface. [We'll ignore for now that broken electrical receptacle cover hazard.]

[Click to enlarge any image]

Use the CONTACT link to send me some photos of your baseboards and we can comment further.

Reader Question: contractor re-routed baseboard piping, now some rooms don't heat-up

I just bought a house with baseboard heat, oil boiler. I have no experience with this type of system. We hired a contractor to remodel our kitchen and in the process he replaced some pipe in the baseboard area. We asked that a portion of the baseboard heaters be removed so that cabinets could be installed along that wall. Instead, he replaced the pipe and lowered the pipe that runs along the wall with the new cabinets so that the pipe is touching the hardwood floor beneath. The cabinets are installed above the pipe- he cut out a notch for them. My first question is: is this safe?

My second question is: since he replaced lines, the thermostat in that area of the house always reads about 10 degrees lower than the setting. I have check the valves- they are all open. He says he bled the lines of a lot of air and yet still it is not right. Any ideas what he can do to get the temperatures to even out? - Anon: 5 Mar 2015


The contractor would have trouble completely "removing" a section of baseboard if that section was carrying hot water on to heat another portion of the home as s/he would then have to find some new (and more costly) route to get the heating water to that second area. That's why it's more common to do what you described. As long as the heating pipes have adequate clearance to quietly handle their slight expansion and contraction as the piping heats and cools you'll avoid an annoying noise problem.

The temperature of water in your baseboards is unlikely to be much over about 180F and is not going to start a fire. If you had some different safety concern in mind let me know.

Second if temperature in the house is never reaching the thermostat setting for that area then the heat would run continuously - which would be costly. It's possible, especially if the baseboard piping was cut and drained during the work you describe and moreso if there are long horizontal runs, that the system is airbound or partly air-bound. The symptom would be that the boiler and circulator run and zone valves open (if you've got zone valves) but baseboard doesn't get hot.

See AIR-BOUND HEATING SYSTEMS [live link is at "Continue reading" just below]

A second possibility is that if you removed too much baseboard from the heating zone controlled by the thermostat that you cite, the problem could be that the heat-loss rate of the home in that area simply exceeds the heat supply rate from the remaining baseboard sections.

If that's the problem then you'd see that your baseboards are hot and the boiler runs for long intervals or constantly but the room just doesn't get warm. If that's the trouble you'd need to add more baseboard, improve insulation, stop air leaks, or add auxiliary heat.


If you don't know what kind of heat your building uses, we explain how to figure out the answer

If your heating system is not working properly,



Continue reading at AIR-BOUND HEATING SYSTEMS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see AIR BLEEDER VALVES for how to find and operate those cute little controls on baseboards (or radiators)

Or see DIAGNOSE & FIX HEATING PROBLEMS-BOILER if the boiler is just not working like it should

Or see these

Baseboard heat repair articles

Suggested citation for this web page

BASEBOARD HEAT at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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