# GROSS vs NET BTU



## AWWGH (May 2, 2011)

So I'll start by saying I've got differing opinions from a few different people through my work/vendors/engineers we deal with concerning GROSS vs NET BTU.

We currently have taken over a municipal property with a large steam boiler. The current boiler over heats parts pf the building and runs for extended amounts of time. The low/high/low boiler currently maintains the building only on low fire and is down fired with a smaller nozzle (all this was existing when we took over the account). The sight glass soots daily and is cleaned by there maint. guy every day. We've done a heat loss on the building using Manual J and from that this is what I determined.

The radiation for the building is exact, the burner (if running like it should) would be the right burner, and the boiler output (NET) is too small. My opinion is the boiler running on low fire runs too long to heat the building (huge building one zone) causing certain areas to overheat. I believe with the boiler being too small they had problems with the boiler short cycling when running on low/high/low settings.

Here's the questions, if you go by GROSS BTU rating the boiler is correct size, by NET it is too small. I believe the boiler is too small. Unless the boiler was 100% efficient you cannot size it by its GROSS capacity.

Like I said I am getting mixed opinions from people and any input from you guys would be great. Am I correct in my thinking here or not?


I've always gone by NET when sizing.


----------



## user7551 (Oct 21, 2011)

AWWGH said:


> So I'll start by saying I've got differing opinions from a few different people through my work/vendors/engineers we deal with concerning GROSS vs NET BTU.
> 
> We currently have taken over a municipal property with a large steam boiler. The current boiler over heats parts pf the building and runs for extended amounts of time. The low/high/low boiler currently maintains the building only on low fire and is down fired with a smaller nozzle (all this was existing when we took over the account). The sight glass soots daily and is cleaned by there maint. guy every day. We've done a heat loss on the building using Manual J and from that this is what I determined.
> 
> ...


you said it yourself, you can't size any equipment based on gross when its not 100% efficient . I'm not a duct guy but if the ducts aren't 100% efficient wouldn't the system have to be sized for heat loss in the ducts also


----------



## OldSchool (Jan 30, 2010)

AWWGH said:


> So I'll start by saying I've got differing opinions from a few different people through my work/vendors/engineers we deal with concerning GROSS vs NET BTU.
> 
> We currently have taken over a municipal property with a large steam boiler. The current boiler over heats parts pf the building and runs for extended amounts of time. The low/high/low boiler currently maintains the building only on low fire and is down fired with a smaller nozzle (all this was existing when we took over the account). The sight glass soots daily and is cleaned by there maint. guy every day. We've done a heat loss on the building using Manual J and from that this is what I determined.
> 
> ...


What you are talking about is input and output

Input is the amount of btu going in burner

Output is the amount btu put out or recovered by the equipment in heat

The difference in btu is exhausted out side

So you always size equipment by the output

Sent from my portable office....yes I am at work


----------



## OldSchool (Jan 30, 2010)

playme1979 said:


> you said it yourself, you can't size any equipment based on gross when its not 100% efficient . I'm not a duct guy but if the ducts aren't 100% efficient wouldn't the system have to be sized for heat loss in the ducts also


There is no heat loss from ductwork if it is in the building space

Heat loss is the amount of btu that eventually leaves the building envelope over a period of an hour

No matter what the r value is eventually hot goes to cold

More R value the slower the transfer

Therefore the less btu to maintain a given set temperature

Sent from my portable office....yes I am at work


----------



## rjbphd (Feb 5, 2010)

Too many variables on this ... still have the orginanal(sp) boiler? Replacment boiler and proper near boiler pipings? Main vents properly sized and piped? Are ALL the pipes insulated? At what pressure is the system running at? Have the boiler been properly skimmed to prevent priming? What do you mean by cleaning "soot" from sight glass. Another book for your collection will be " the Lost Art of Steam Heating " by Dan Holohan, where I got my 'PhD*' from.


----------



## AWWGH (May 2, 2011)

That's what my thinking was. Everything matches up except the boiler itself. The burner is not designed to run only on low fire which would seem to cause long cycles to satisfy the thermostat and overheat other areas.

It is throwing me off because the burner rep who I believe helped design the system is telling me otherwise. 

The system has never worked correctly since day 1 I'm told also

Sent from my DROIDX using Plumbing Zone


----------



## OldSchool (Jan 30, 2010)

If the boiler is sooting you need to anylze the combustion. More than likely the fuel air mixture is out of wack.

Sent from my portable office....yes I am at work


----------



## OldSchool (Jan 30, 2010)

AWWGH said:


> That's what my thinking was. Everything matches up except the boiler itself. The burner is not designed to run only on low fire which would seem to cause long cycles to satisfy the thermostat and overheat other areas.
> 
> It is throwing me off because the burner rep who I believe helped design the system is telling me otherwise.
> 
> ...


It you are getting over heating in certain areas and not enough in others

Then I would think that it is a piping issue or rad issue or loss of heat from the piping itself before gets to the rads

Sent from my portable office....yes I am at work


----------



## AWWGH (May 2, 2011)

OldSchool said:


> If the boiler is sooting you need to anylze the combustion. More than likely the fuel air mixture is out of wack.
> 
> Sent from my portable office....yes I am at work


What about the fact that the boiler cycles are way longer than they should be due to running only on low fire? 

Does that make any sense or am I crazy?

low/high/low is supposed to be low-startup, high-heat, low-maintain heat correct?


----------



## AWWGH (May 2, 2011)

OldSchool said:


> It you are getting over heating in certain areas and not enough in others
> 
> Then I would think that it is a piping issue or rad issue or loss of heat from the piping itself before gets to the rads
> 
> Sent from my portable office....yes I am at work


The building is about 100 years old and did not have these problems supposedly until this new boiler/burner system was installed about 8 years ago. Problems ever since.


----------



## rjbphd (Feb 5, 2010)

Can you post pictures of the boiler and its near pipings?


----------



## OldSchool (Jan 30, 2010)

AWWGH said:


> What about the fact that the boiler cycles are way longer than they should be due to running only on low fire?
> 
> Does that make any sense or am I crazy?
> 
> low/high/low is supposed to be low-startup, high-heat, low-maintain heat correct?


It sounds like the boiler is maintaining on low fire because there is already enough heat. It at it's temp already

Reason being that you have over heating in certain areas leads me to believe that the boiler temp is fine. Just that stat in cool area is still calling

Sent from my portable office....yes I am at work


----------



## AWWGH (May 2, 2011)

rjbphd said:


> Can you post pictures of the boiler and its near pipings?


I will probably be back on site next week (possibly before) so I will take pictures. I don't believe I have anything helpful currently.


----------



## OldSchool (Jan 30, 2010)

AWWGH said:


> The building is about 100 years old and did not have these problems supposedly until this new boiler/burner system was installed about 8 years ago. Problems ever since.


Did you check the condensate return line temperature?

You might have defective steam traps in the area you are trying to get heat to

Sent from my portable office....yes I am at work


----------



## AWWGH (May 2, 2011)

OldSchool said:


> It sounds like the boiler is maintaining on low fire because there is already enough heat. It at it's temp already
> 
> Reason being that you have over heating in certain areas leads me to believe that the boiler temp is fine. Just that stat in cool area is still calling
> 
> Sent from my portable office....yes I am at work


I guess my thinking is that when on low fire it does not deliever the heat to the system fast enough, therefore it keeps pumping out heat to the areas that overheat before it can finally satisfy the area where the t-stat is.


----------



## AWWGH (May 2, 2011)

OldSchool said:


> Did you check the condensate return line temperature?
> 
> You might have defective steam traps in the area you are trying to get heat to
> 
> Sent from my portable office....yes I am at work


All return lines/traps seem ok. We have replaced quite a few that rotted out since we have been working there.


----------



## rjbphd (Feb 5, 2010)

Problems ever since the new boiler and burner.... huh ohhh...


----------



## AWWGH (May 2, 2011)

rjbphd said:


> Problems ever since the new boiler and burner.... huh ohhh...


Installed by others. 

But now our problem.


----------



## AWWGH (May 2, 2011)

rjbphd said:


> Another book for your collection will be " the Lost Art of Steam Heating " by Dan Holohan, where I got my 'PhD*' from.


Consider it ordered.:thumbsup:


----------



## OldSchool (Jan 30, 2010)

AWWGH said:


> All return lines/traps seem ok. We have replaced quite a few that rotted out since we have been working there.


Best way get your self an hand held infra red temperature gauge and going around checking all condensate lines after the steam traps

Traps may be plugged up. If the trap is plugged up then the pipe will be cold

Sent from my portable office....yes I am at work


----------



## AWWGH (May 2, 2011)

OldSchool said:


> Best way get your self an hand held infra red temperature gauge and going around checking all condensate lines after the steam traps
> 
> Traps may be plugged up. If the trap is plugged up then the pipe will be cold
> 
> Sent from my portable office....yes I am at work


I will look into that. Wouldn't the system knock and bang real bad if it there was not condensate return in areas?


----------



## OldSchool (Jan 30, 2010)

AWWGH said:


> I will look into that. Wouldn't the system knock and bang real bad if it there was not condensate return in areas?


Knocking and bang is when the steam trap is stuck open and steam is getting into the condensate line 

That noise is the pipe expanding and contracting because of the change in temperature

What I am saying is that the trap is blocked and nothing is getting through

Sent from my portable office....yes I am at work


----------



## rjbphd (Feb 5, 2010)

I bet its the near boiler pipings and main vents problem...after all, the rest of the system been there 100 years without any problems...unless they remove the insulation


----------



## BROOKLYN\PLUMB (May 21, 2010)

rjbphd said:


> I bet its the near boiler pipings and main vents problem...after all, the rest of the system been there 100 years without any problems...unless they remove the insulation


My money is on os


----------



## user7551 (Oct 21, 2011)

OldSchool said:


> There is no heat loss from ductwork if it is in the building space
> 
> Heat loss is the amount of btu that eventually leaves the building envelope over a period of an hour
> 
> ...


So you wouldn't have any heat loss in an old duct system that say wasn't properly insulated or say if there leaks in the ducts or in a cold area like above the ceiling . Just wanting to understand a little more about the subject.


----------



## user7551 (Oct 21, 2011)

OldSchool said:


> There is no heat loss from ductwork if it is in the building space
> 
> Heat loss is the amount of btu that eventually leaves the building envelope over a period of an hour
> 
> ...


So you wouldn't have any heat loss in an old duct system or the piping system that say wasn't properly insulated . Just wanting to understand a little more about the subject.


----------



## OldSchool (Jan 30, 2010)

playme1979 said:


> So you wouldn't have any heat loss in an old duct system or the piping system that say wasn't properly insulated . Just wanting to understand a little more about the subject.


Heat loss/ Heat Gain

Is a term and figured out with a formula to figure out how much btu is needed to heat or cool the building

This calculation is used to keep the inside of the building at a determined temperature for a given out door temperature...

It doesn't matter where these BTU come from to heat the building .... it could be a space heater, fireplace or if you want distribution and comfort then forced air furnace or boiler

Any loss from piping or duct work is still inside the building ... it is not lost

However with a distribution system such as a boiler or forced air system if you are losing heat from piping or ducts then the zone or area it was intended for would be lacking....

The heat is still in the building ... just not going to the intended place of distribution...


----------



## AWWGH (May 2, 2011)

OldSchool said:


> Heat loss/ Heat Gain
> 
> Is a term and figured out with a formula to figure out how much btu is needed to heat or cool the building
> 
> ...


Within the building envelope is how we determine. If its conditioned space then yes its part of the load calc. If its "in" the building but "outside" the envelope (such as a vented attic) then we dont include it.


----------



## AWWGH (May 2, 2011)

AWWGH said:


> Within the building envelope is how we determine. If its conditioned space then yes its part of the load calc. If its "in" the building but "outside" the envelope (such as a vented attic) then we dont include it.


Sorry meant to quote Playme1979


----------



## OldSchool (Jan 30, 2010)

AWWGH said:


> Within the building envelope is how we determine. If its conditioned space then yes its part of the load calc. If its "in" the building but "outside" the envelope (such as a vented attic) then we dont include it.


 :laughing: well you would certainly not be heating your attic space.... at least I hope not


----------



## AWWGH (May 2, 2011)

OldSchool said:


> :laughing: well you would certainly not be heating your attic space.... at least I hope not


I was just saying that because in my area we see a lot of attic spaces spray foamed in the roof line and no insulation between the living space and attic.

We don't condition this attic space but it must be incorporated within our load calculations.

I don't personally agree with a house built like that, but we see it a lot.


----------



## AWWGH (May 2, 2011)

They make houses too tight today, but that's a whole other problem.


----------



## OldSchool (Jan 30, 2010)

AWWGH said:


> I was just saying that because in my area we see a lot of attic spaces spray foamed in the roof line and no insulation between the living space and attic.
> 
> We don't condition this attic space but it must be incorporated within our load calculations.
> 
> I don't personally agree with a house built like that, but we see it a lot.


They have started doing that around here also....

There would be no cross ventalation from soffits...

I just wonder how the shingles are going to react.... you would think they would overheat and curl up


----------



## AWWGH (May 2, 2011)

OldSchool said:


> They have started doing that around here also....
> 
> There would be no cross ventalation from soffits...
> 
> I just wonder how the shingles are going to react.... you would think they would overheat and curl up


These "efficient" homes have higher heating/cooling loads since they are so tight and we have to bring in fresh air.

They can't understand why the heating load gets higher when we bring in 0 degree air in the winter.

These houses are so tight they have to either open a window to light a fire or we install fans to create a draft.

Ridiculous!


----------



## OldSchool (Jan 30, 2010)

AWWGH said:


> These "efficient" homes have higher heating/cooling loads since they are so tight and we have to bring in fresh air.
> 
> They can't understand why the heating load gets higher when we bring in 0 degree air in the winter.
> 
> ...


Up here we have to install HRV system.... to give the home air exchange... either that or the condensation collects on the windows and the humidity rises in the home


----------



## AWWGH (May 2, 2011)

OldSchool said:


> Up here we have to install HRV system.... to give the home air exchange... either that or the condensation collects on the windows and the humidity rises in the home


Yeah, same here.

Either hydronic coil in the duct or electric.


----------



## OldSchool (Jan 30, 2010)

AWWGH said:


> Yeah, same here.
> 
> Either hydronic coil in the duct or electric.


:blink: what :blink:


----------



## AWWGH (May 2, 2011)

OldSchool said:


> :blink: what :blink:


After the hrv, to help condition the air before it leaves the duct.

Sent from my DROIDX using Plumbing Zone


----------



## OldSchool (Jan 30, 2010)

AWWGH said:


> After the hrv, to help condition the air before it leaves the duct.
> 
> Sent from my DROIDX using Plumbing Zone


Oh I see.... preheater to bump up incoming air temp


----------



## AWWGH (May 2, 2011)

OldSchool said:


> Oh I see.... preheater to bump up incoming air temp


Yes sir. 
Sorry I was pretty vague before.

Sent from my DROIDX using Plumbing Zone


----------



## OldSchool (Jan 30, 2010)

AWWGH said:


> Yes sir.
> Sorry I was pretty vague before.
> 
> Sent from my DROIDX using Plumbing Zone


so vague I had to go :blink::whistling2:


----------



## AWWGH (May 2, 2011)

OldSchool said:


> so vague I had to go :blink::whistling2:


Ha, it's getting late and I had a couple cocktails with dinner.

Sent from my DROIDX using Plumbing Zone


----------



## user7551 (Oct 21, 2011)

I have always wondered about what kind of system you would have to have if you basically built a house like you would a refrigerated cooler.


----------



## rjbphd (Feb 5, 2010)

How did we stray from the steam system subject into bunch of hot air systems on this thread???


----------



## OldSchool (Jan 30, 2010)

rjbphd said:


> How did we stray from the steam system subject into bunch of hot air systems on this thread???


 
Thats why you got to start reading a thread from the first post all the way through to the last.... if you want to follow along


----------

