When chosing a Hot Air Furnance oil fired ,is the main concern C

Unknown

Sell the customer the comfort with hot water heating system.. No cfm worry here..

jim_160

hot air furnace

when changing out a oil furnace, is the cfm"s a main concern? i want to provide the customer with a comfortable replacement. the different vendors have simalar cfm"s with belt drive motors

Mitch_4

Many a time I comment on this

While CFM is not the main concern,(matching a unit to the heat loss is), It is one of the biggies. Noise is generally attributed to the air movement through the duct system. All too often installers replace on a like for like basis, not realizing that newer units have a lower temperature rise that results in a higher CFM. When you couple this fact to a duct system that was likely designed around a .2" ESP, and at the time of upgrade they add A/C changing the design requirements to a .5"ESP, you have a recipe for disaster.

When matching the CFM, you may need a lower firing rate, however it is quite likely that that is not an issue as the original is way oversized and structural improvements make a smaller input unit desirable.

If the existing unit is running, calculate the CFM using the formula CFM = output / (1.085 x delta T)

If the unit predate AFUE, likely the listed output exceeds actual, and odds are that the original spec nozzle on the rating plate was reduced to eliminate short cycling... in which case use the nozzle size x 140,000 x.7. Modern AFUE rated units you can use the rated output of the unit.

If you cannot fire the unit to measure delta T, then use the mid range number on the rating plate (ie if state 100-130, use 115)

The important thing is that the CFM you determine is approximately what the customer is used to hearing, it is the velocity hea / she hears at the registers.

Do it right and you will have an extremely satisfied customer.

Mitch_4

assuming

that the it is installed correctly too, and the customer wants to drop thqt amount of scratch to completely convert his existing system to something that is not there...Not too likely these days

Bob Bona_4

is air

conditioning involved?

Residential belt drive blowers = dinosaur. Would not even consider it. Direct drive multispeed should be your standard if not for A/C, just for flexibility, ease of service, and quietness. Kick it up a notch and look at Thermopride's variable speed blower set up.

The furnace is sized for the heat loss, look at the blower drive capacity to see if it can handle the A/C tonnage required for the house. In most cases, the required heat GPH (BTUH) and the max CFM's the given blower has are available in the same model size.

So, the main concern is correct heat sizing, with one eye on CFM's for cooling. Disclaim the heck out of existing ductwork..I don't think I've seen the last of crazy and inadequately sized and installed ductwork- it will make you and your new furnasty look foolish.

HTH.

joel_19

ducts

We have a ductblaster an infiltrometer blower door and great stuff for checking static etc. i have tested lots of exsisting duct systems those that pass = 0