Archive for the ‘HVAC’ Category

What is a limit switch and why does it shut off my furnace?

April 25, 2011

What is a limit switch and why does it shut off my furnace?

Trane SWT 01635 thermal limit switch,

photo of item KSS#72-092

The limit switch is a small, silver bi-metal disc about the size of a dime or quarter which turns off the furnace if the temperature inside the furnace gets too hot (see another example)  It is a safety device and should not be disabled or bypassed.  Limit switches do go bad sometimes, especially if the furnace routinely overheats.  However, you should try to determine why your furnace is getting too hot before you replace the switch.  An overheated furnace is usually the result of inadequate air flow through the furnace or a furnace that is too large for the building.  An overheated furnace is not only inefficient, it will shorten the life of the heat exchanger in the furnace.

The first thing to check is your registers.  Make sure all registers are open and not blocked by furniture or other items.  Be sure the filter in the furnace is clean.  If you have recently added air-conditioning to your system, it may be possible to increase the blower motor speed.  Get a furnace technician to do this if you are unsure how to safely change the speed.

If you have tried all of the above and replaced the limit switch but the furnace still overheats, the size of your ductwork or furnace is suspect.  Do you have at least as much cold return air coming back to the furnace as there is warm air going to the home?  If not, add more cold air runs or increase the size of existing runs.  You may also need more warm air runs to get the heat away from the furnace.  The main trunk or ductwork may be too small to handle the needed air flow.  Call a trusted HVAC technician to do a heat loss and/or heat gain assessment for your house to see if the ductwork and furnace are properly sized.

More information can be obtained at the links below:

More about high limit switches at

Interesting forum entry regarding limit switch on


Duct tape, ductboard tape, flex duct tape-what is the difference?

April 25, 2011

Duct tape, ductboard tape, flex duct tape-what is the difference?

You might have heard the joke that all a DIY person needs is duct tape and WD40.  If something is supposed to move and doesn’t, use the WD40.  If it moves and isn’t supposed to, use the duct tape!

Before the advent of fiberglass ductboard and insulated flex duct, gray cloth duct tape was pretty much all we needed for tin ductwork and a million other uses around the home, and it is still great stuff to have on hand.  Today there is also ductboard tape, sometimes called aluminum foil tape, as well as flex duct tape.

As the name implies, ductboard tape was designed to construct and seal fiberglass duct work.  This tape is pressure sensitive which means you must go over it with a small squeegee to make a good seal.  Ductboard tape is available with or without the UL 181 approvals.  The UL 181 is clearly marked on the outside of the tape and must be used when the ductwork will be inspected.  Surprisingly, the non-UL 181 tape has a higher adhesion rating than the UL 181 approved tape.  Most of our local contractors prefer the nonlisted tape unless a job must be inspected.  Our flex duct tape is a very sticky, black tape designed to bond, protect, hold and patch flexible duct pipe.  Flex duct tape is not recommended for metal duct.

Now you can get the right tape for the right job.  We will discuss the WD40 later!

Baseboard BTU’s

April 25, 2011

Often we are asked how many BTU’s are in a foot of baseboard heating.

To answer this, the following must be considered:  is the baseboard heating system electric, steam or water?  For this post we limit it to hot water baseboard.

Finding (1) the temperature and rate of the water passing through the baseboard, (2) the size of the copper tube and (3) the specifications of the baseboard from the manufacturer will provide a more precise answer.

We sell Argo Low Trim II baseboard which can produce 570 BTU/hr at a water temperature of 180 degrees, at a pump rate of 1 gal per minute.   You can find this information at Argo’s website for Low Trim II.

This amount of BTU’s per foot, combined with a heat loss calculation, can determine how many feet of baseboard are needed to heat a room. Heat loss calculation is a complicated number to determine.  It involves knowing the average outside winter temperature, how the room is insulated, square footage of the room, and number of windows and doors.  There are heat loss software programs that are used to input all the variables to get a result of  BTU’s required to heat a room or house.   One can use a rough estimate of 50 BTUs/hr per square foot.  Keep in mind that a rough estimate is just that, an estimate.

An example is that if you have a room that is 20 x 24 and are trying to determine the amount of baseboard, a rough estimate of BTU’s required would be (24×20)  *50 BTU’s/hr = 24000. The number of baseboard feet would be 2400 / 570, or 42 ft of Argo baseboard.

Baseboard is often installed under windows. Can you guess why?  Look for future posts to get the answer.

Links that provide more information:

  • Article containing more complexities of answering the same question:
  • Interesting conversation regarding baseboard BTU’s –

With Oil Nozzles, size does matter

March 24, 2011

Can I Change the Size or Type of My Oil Nozzle?

In general, the oil nozzle recommended by the heater manufacturer should be used.  This can usually be found on a tag on the heater.  The nozzle is rated by GPH (gallons per hour of fuel use), spray angle and spray pattern.  For example, a .60 80 B nozzle will deliver .6 GPH oil use with an 80 degree angle and solid spray.

You may experiment with a smaller GPH nozzle to achieve better fuel economy.  A 1.20 GPH nozzle may be replaced with a 1.10 GPH, etc.  You may also try using a “W” nozzle in place of a hollow (A) or solid (B) spray pattern.  Other changes, especially to the spray angle should be left to an experienced technician.

More information can be found on the links below:

“Total Look at Oil Burner Nozzles”- by Delavan

Oil nozzle size–effect on consumption – Gardenweb discussion group

Nozzle sizes are stamped on the nozzle: – forum

When you purchase oil nozzles from our web site, in order to keep shipping costs low, we ship them using  US Priority mail.  Please provide a valid mailing address when you place you order.

Delavan Adaptrap

March 24, 2011

Delavan Adaptrap

When oil continues to drip or ooze after the burner shuts off, try replacing the standard nozzle adapter with a Delavan Adaptrap.  The Adaptrap also helps eliminate erratic spray and flame flutter on burner shut-off due to air in the oil line.

Any time you experience air in the oil line it is a good idea to check for leaks especially around fittings and valves.  Use a clean cloth or paper towel to dab under each fitting to detect any oil present.  Tighten or replace any leaky components.

Delavan Nozzle Line Filter

March 24, 2011

Delavan Nozzle Line Filter


Delavan oil line filter

When contaminated oil nozzles are about to drive you over the edge, try adding an inexpensive line filter to your system.  The Delavan nozzle line filter provides four times the straining area and removes particles one-half the size as a standard nozzle strainer.

The 1/8″ filter is easily installed in the nozzle port of the oil pump between the pump and the nozzle.  Line filters can be used on burner applications of 2.00 GPH or less and should be changed at least annually.

A little ditty:

A warm cozy house brings peace of mind,
A well maintained furnace purrs along fine.
But if you awake to an ice cold house,
You’ll be spending the day with one angry spouse.

Noisy Oil Pump Operation

March 24, 2011

Noisy Oil Pump Operation

One cause for a noisy pump is a misaligned oil burner coupling.  Try loosening the mounting screws slightly and shift the pump position until the noise is eliminated.  Retighten screws.

oil burner pump couplers

Air in the inlet line can also cause noise.  Check all fittings and connections for leaks.  Tighten or replace any leaky fittings.

A humming noise can be fixed by installing a Silent-Flo anti-hum device.

Anti Hum device

For more information on oil pumps:

Suntec Field service and Trouble Shooting Guide

Suntec Oil Pump Strainers

March 24, 2011

Suntec Oil Pump  Strainers

Checking the strainer in your fuel pump should be part of the routine annual maintenance of your oil furnace or boiler.  It should also be checked if you are not getting a good oil flow at the nozzle or you have pulsating pressure.  To check the strainer, remove the four screws on the front cover with a 5/32 Allen wrench.

Suntec Pump




strainer for Suntec Pump





You can clean the strainer with a brush and clean fuel oil or replace it with an inexpensive new strainer.  Look at the first letter of the Suntec model number to determine the right strainer.  There are different strainers for the A-series, B-series and J or H-series pumps.

For more information:

Suntec Field Service and Trouble Shooting Guide

Height of Chimney?

March 24, 2011

How high above the roof does my chimney have to be?

The following information is for the typical chimney installation.  Always check your local codes.

Table from Metal-Fab, Inc.

Roof Pitch Minimum Height for gas chimneys, B-vent

Flat to 7/12 (305 mm) 1.0 feet

Over 7/12 to 8/12 (451 mm) 1.5 feet

Over 8/12 to 9/12 (610 mm) 2.0 feet

Over 9/12 to 10/12 (762 mm) 2.5 feet

Over 10/12 to 11/12 (991 mm) 3.25 feet

Over 11/12 to 12/12 (1218 mm) 4.0 feet

Over 12/12 to 14/12 (1524 mm) 5.0 feet

Over 14/12 to 16/12 (1829 mm) 6.0 feet

Over 16/12 to 18/12 (2134 mm) 7.0 feet

Over 18/12 to 20/12 (2286 mm) 7.5 feet

Over 20/12 to 21/12 (2438 mm) 8.0 feet

Metal-Fab B-vent (gas vent) instructions

For oil, wood or coal chimneys the top of the chimney must be at least 3 feet above the highest point of contact with the roof and at least 2 feet above the highest roof surface or other obstruction within 10 feet horizontally from the top of the chimney.

For more detailed installation instructions visit:

Metal-Fab Temp/Guard all-fuel chimneys

Metal-Fab L-vent for oil chimneys

We stock Metal-Fab B-vent for gas and Metal-Fab Temp/Guard for oil, coal and wood.  Temp/Guard is rated for 2100F intermittent and 1000F continuous temperatures.

Oil Nozzle – Care

March 23, 2011

Oil Nozzle Care and Tips

Oil nozzle wrench next to electrods

Delavan Oil Nozzle Changing wrench

Oil nozzles are designed to do an accurate job of atomizing and metering fuel oil in the spray pattern of your burner. Keep nozzles in their original containers. Handle the nozzle by the hex flats and avoid touching the strainer. Use clean tools.



Using oil nozzle wrench to remove oil nozzle
Using the oil nozzle wrench


We recommend using a Delavan nozzle changer wrench to protect the porcelain electrodes.




Using box end wrenches to remove oil nozzle

using box end wrenches



If you do not have a nozzle changer wrench, you may also use two box-end wrenches.



Nozzles and oil filters should be changed at least annually for optimum service and efficiency. Add a good fuel oil treatment (our item number 47-330) to your oil tanks every year to keep filters and nozzles free from sludge and water.


We do not recommend trying to clean and reuse nozzles.  It is better to keep a spare on hand during the heating season.

Other information can be found below: