Hot Water Baseboard Heat

Heating Baseboard Inspect, Repair, Cleaning

How Does Finned Copper Tubing 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 Associates' sketches (further below) show 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 room air enters at the baseboard bottom (blue arrow in our photo), is warmed as it passes over and through finned copper tubing, and exits at the baseboard top (orange arrow in our photo).

As we discuss in more detail on this page, to get the most heat out of baseboard like that in the photo, we need at least 3/4" of clear space between the bottom of the baseboard cover and the floor surface - to allow to enter the baseboard,

and we need to open the hinged louvers that control the baseboard heat output at the top of the baseboard.

How Does Cast Iron Heating Baseboard Work?

Carson Dunlop Associates' 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, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ].

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:

• The number and square feet of windows in the room and the window's R-value
• The room's insulation levels or R-values for its walls, floor, ceiling
• The room ceiling height
• The level of air leakage into or out of the room
• The heat output per linear foot of the model of heating baseboard chosen
• The flow-rate and temperature of hot water passing through the heating baseboard.
• Electric baseboard heat linear feet requirements are discussed at FEET of BASEBOARD HEAT NEEDED?

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.

Cold Baseboard Heat Room on a Single Zone - Replace the Aquastat?

Reader question: 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 replaces 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 two 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 2/13/2014

Reply: unlikely but possible

Really? I'm sorry to say that 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 shock hazard.]

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

Contractor re-routed baseboard piping, now some rooms don't heat-up

Reader Question: 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

Reply:

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 more so 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 for procedures to remove air that prevents hot water from flowing through heating baseboards.

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.

More Cold Heating Baseboard Diagnostics

Cold Heating Baseboard Diagnostic Guide: how to diagnose a heating baseboard section, loop, zone, or room that is not receiving heat.

Watch out: as shown in our photo: this older baseboard heat installation is missing its end-cover That won't have much effect on heat transfer but it might mean that a barefoot walker could cut her toes on the exposed fins - they're quite sharp.

Also we notice that a layer of tile flooring has been added, reducing the air inlet space at the bottom of the baseboard, thus slowing its ability to deliver heat to the room.

Here are more things to check if your baseboard heaters are cold and you need 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.

See THERMOSTATS.

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

at AIRBOUND HEAT SYSTEM REPAIR by WATER FEED VALVE.

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,

see AIR SCOOPS SEPARATORS PURGERS.

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.

See THERMOSTATS.

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.

Other Heating Baseboard Defects

• Air-bound heating baseboards can prevent sections or entire loops of heating baseboards from getting hot. Details are
  
  at AIRBOUND HEAT SYSTEM REPAIRS

• Missing baseboard covers:
  
  the covers are required to assure proper heating of room air by convection.
  
  See RADIATOR BASEBOARD or CONVECTOR COVERS for tips on how to make or buy replacement covers for hot water heating baseboards
• Missing baseboard end caps:
  
  same as above (photo above right)

• Damaged or dust-clogged heating baseboard fins -
  
  reduces air-flow and thus heating output. It's easy to fix this problem by careful vacuuming of the heating baseboard fins using a crevice tool on your home vacuum cleaner.
  
  Watch out: be gentle or use a special brush attachment when vacuuming heating baseboard tubing and fins, or remove the baseboard covers if necessary.
  
  If you are heavy-handed with the vacuum cleaner you may bend and damage the fins covering the baseboard tubing, resulting in reduced heat output.
• Inadequate clearance
  
  between the baseboard bottom and the floor surface - blocks entry of cool air into the baseboard
• Leaky hot water baseboard
  
  connections, air bleeders, elbows.
  
  See LEAKS at BASEBOARD, CONVECTOR, RADIATOR for details.

• Inadequate total linear feet of heating baseboard for the room size -
  
  inadequate heat output may leave the room too chilly on cold windy days.
  
  Solutions to inadequate hot water heating baseboard installations include increasing the hot water flow rate through the baseboard by changing the circulator pump to a higher output unit, increasing the water temperature flowing through the baseboard, increasing the diameter of piping between the heating boiler and the baseboard input and output ends, or changing the baseboard itself to a higher BTU output (per linear foot) model.
  
  Our photo shows heating baseboard being installed in a Poughkeepsie, NY home. The linear feet in this room was held to a minimum for room design reasons, leading the builders (DF & Galow Homes) to select a higher-output baseboard design.
  
  Watch out: Unfortunately the installing Poughkeepsie plumber took some shortcuts and "saved money" by reducing the hot water piping feed and return piping from our design point of 3/4" diameter to his own preference for (easier and faster to install) 1/2" diameter piping.
  
  We may need to install a higher capacity output circulator pump at this home or perhaps we'll need to install larger diameter supply and return piping. This installation remains under evaluation.
• Unsafe electric heating baseboard installation details & clearances
  
  such as from curtains and electrical outlets or wires.
  
  See ELECTRIC BASEBOARD HEAT SAFETY

Baseboard Heat Clearance Distance to Floor Surface Affects Heat Output

Shown in our photo: we need to maintain an air inlet at the bottom of the baseboard heater. If adding carpet or flooring will block this opening that will cut heat output and will thus also increase the cost of heating the room.

Reader question: Will an additional layer of flooring degrade our baseboard heat performance?

We currently have hot water baseboard heat. We are installing new flooring 3/4 thick over existing flooring.

Will this significantly degrade the efficiency of the heat by reducing the airflow to the bottom of the baseboards? - On 2020-09-18 by New flooring

Reply by (mod): Recommended clearance space between baseboard heat cover and floor surface = 3/4" to 1"

Yes. If the air entry space at the bottom of heating baseboards is substantially reduced then you will indeed reduce the baseboard heat output, increasing heating cost and slowing the delivery of heat to that room.

You want to keep at least 3/4", better 1" of space between baseboard cover bottom edge and the upper floor surface.

So if your original baseboard heat clearance distance from the bottom edge of the front cover of the baseboard and the floor surface was one inch and you add 3/4" of flooring (or carpeting) you're reducing the space to just 1/4" - which is too small; you're cutting the heat output by perhaps 75%.

When our clients installed wall to wall carpeting we recommended stopping the carpet padding a couple of inches short of the front of the baseboard, thus reducing the carpet thickness and maintaining about 3/4" clearance space.

But when you're installing new wood flooring that's 3/4" thick, normally the floor would continue all the way to the wall.

While it adds cost to the job, best would be to raise the heating baseboard higher on the wall to avoid loss of heat or increased heating bills.

Details about improving heat delivery where baseboards may be blocked by flooring

It's going to be expensive to remove and reinstall all of the baseboard heaters in a building to raise them up on the wall to clear carpeting or additional layers of flooring.

Where the added floor covering is carpet, we often cut back the carpet padding or even remove carpeting from the wall to about an inch in front of the baseboard.

If wood flooring was added under the baseboards right up to the wall, it's likely that flooring fasteners were not "nailed" from under the baseboard itself - you just can't reach under there to do so.

So it might be possible to cut out flooring along the edges of the room to permit air to enter the underside of the baseboards as intended. Otherwise I agree with you that blocked baseboards increase the building heating cost by requiring the boiler to run longer and baseboards to remain hot longer to heat the space.

Also worth considering is to make sure that you're running your boiler at its highest reasonable temperature, say close to 200 deg F.

That's because the thermal conductivity and delivery of heat from hot water heating baseboards is exponentially greater at higher temperatures. That is, the rate of heat transfer improves at higher temperature.