Heating loads and furnace size

[ktm250rider]

When getting a heating and cooling load calcuation done, what do you look at when sizing the furnace? I have one vendor that recommends a 125 KBtu furnace and my heating loads show from 67 to 82 KBtu per hour required.

[Jultzya]

From your other post and this one, you better be looking for a new HVAC contractor!

Who in their right mind would install a 125K unit for a 67-82K load?

Also, as I stated in your other post, there is something seriously wrong if the two load calc's were 26 & 42 K for cooling.

I believe someone is guessing!

[Jultzya]

If you'd like to know for yourself, click on the bullseye at the top right of your browser.

Do the load calc yourself and see what you come up with.
(let us know the results)

[ktm250rider]

Who in their right mind would install a 125K unit for a 67-82K load?

So I take it that 125K is oversized?

THis was an off the cuff estimate as he was standing in the room looking around. Of course when i called him for the written quote, the price went up.

[Irishmist]

Ultimately, whoever is going to do the install of this unit, is responsible for the correct sizing and operation of the unit. It is difficult if not impossible for any of us to make recommendations since we do not have access to the property. We would obviously calculate our own loads and make a recommendation based on the results.

One thing to keep in mind is input versus output. The load calculation that you arrive at is the amount of heat loss that needs to be made up, and this amount will theoretically match up with your output rating of the furnace with the efficiency factored in. Then you also have to take into account the AFUE rating of the furnace to determine how much 'usuable' heat is generated to offset the heat loss.

If there is some question with any contractor as to how they arrived at their recommendations, simply ask. If they are willing to stand behind their calculations, and there are no other issues, then as I said, they ultimately are the ones that are responsible for the proper operation.

Question: Did you ask for a rough estimate while he was at the house, or did he offer that on his own. This is a good example why it does neither the owner or the contractor any good to try to 'guesstimate' a price instead of waiting to sit down and concisely figure the total job. The fact that his price went up, is not a big surprise. I know when I have a chance to sit down and accurately figure the job, there are potentially a lot of areas I think of that did not necessarily come to mind when I tried to give a 'ball park' price.

All of us, I would venture without exception, have been asked to give one of these "wags." Wild A_ _ guess.

[Jultzya]

Originally posted by John Lloyd
One thing to keep in mind is input versus output. The load calculation that you arrive at is the amount of heat loss that needs to be made up, and this amount will theoretically match up with your output rating of the furnace with the efficiency factored in. Then you also have to take into account the AFUE rating of the furnace to determine how much 'usuable' heat is generated to offset the heat loss.

True, but the minimum efficiency of a gas fired furnace is 80%.

A 125K input 80% would give you 100K output.

His loads was anywhere from 67-82K. At a maximum, 100K input 80% = 80K ouput.