# Boiler size



## qbert (Mar 23, 2009)

Standing radiation can be used but usually it ends up oversizing the system. I am sure the has been some form of upgrades to the home since the original install. Man j or other approved method should be used before selecting any boiler. It is no different than forced air in that aspect. There are several contractors in your area that can preform this for you.


----------



## Bonnie Youngs (Jul 7, 2009)

thank you. all of our unprofessional calcs done so far have indicated 140-150K range. i'll be sure to ask from now on what method is being used to assess the need.

BY


----------



## qbert (Mar 23, 2009)

Boilers net IBR or output should meet or exceed your load. Good luck


----------



## Bonnie Youngs (Jul 7, 2009)

sorry, one clarification. if we need net 140K to properly heat the house, that means we need to buy a 'gross' unit of 160K at 87% efficiency. this is what you mean by _Boilers net IBR or output should meet or exceed your load_, correct?


----------



## qbert (Mar 23, 2009)

yes remember they are not 100% efficient


----------



## tk03 (Sep 30, 2008)

Let's clear this up. When a manual J is done the contractor needs to measure all the doors windows walls etc. They run this through a computer program to determine the heat loss. You then size the boiler off the DOE output not IBR output unless the boiler is not in the house.
The efficiency does not play in any way in this step. The efficiency is only how much you will save when operating. If the heat loss is let's say 50,000 you choose a boiler with a DOE of 50,000 or close. If that boiler is 95% efficient or 50% efficient it will put out 50,000 if that is the rate. All boiler manufactures have the output listed at the given efficiency. The 50% efficiency boiler will give you the same amount of output if it is rated the same it just takes more fuel to get there. A 95% product will give you the 50,000 btu's at less fuel input.
The other thing we need to realize with boilers is the efficiency is never the same. Boilers are tested with an AFUE test. This test is done at 120º return water temperature and 140º supply water temperature. When the boiler is operating at that temperature that is the efficiency providing the piping and flow is correct. As soon as the water temperature increases the efficiency decreases and if the water temperature decreases the efficiency increases. Mod/con boilers can hit efficiencies as high as 99% and in theory over 100%. This is due to the condensing mode you can get heat out of the condensate which normally would not be taken out in the older boilers. This can account for about 9% more heat out of the gas. To take advantage of the higher AFUE efficiencies and the latent heat from the condensate the boiler water must remain below about 130º. Many older and existing homes cannot heat in that range depending on the amount or type of radiation.


----------



## Bonnie Youngs (Jul 7, 2009)

ok, now my head really hurts .

i believe i understand what you're saying. in doing the measuring, then, as you noted, will the radiation capacity of the house be taken into consideration?


----------



## beenthere (Oct 11, 2008)

Don't use the DOE rating.

Your house has large steel pipes.
Use the IBR rating it allows for teh extra heat the pipes will take from the water.

The house should be measured for its heat loss.
Then a boiler is selected to meet that heat loss. And by using the IBR rating, the piping gain is allowed for.

Seem a lot of older hopmes where teh DOE rating was used. And they had problems heating when it got to the lower outdoor temps.


----------



## Bonnie Youngs (Jul 7, 2009)

okay, i'll do more research on the IBR and do a heat loss analysis. at least i'll have lots of questions for tomorrow's estimate guy! thank you.


----------



## Scuba_Dave (Jan 16, 2009)

My house was 1640 sq ft
With an addition/sunroom its increasing to ~3000 sq ft
The same boiler will heat the whole house still
New windows, more insulation in the addtions - including 2nd floor
Our boiler was about 2x as big as it needed to be


----------



## Bonnie Youngs (Jul 7, 2009)

what size boiler do you have? and where do you live?


----------



## Bonnie Youngs (Jul 7, 2009)

sorry, i see now, a cold state!


----------



## tk03 (Sep 30, 2008)

Do not use the IBR. You must use the DOE. Some of the areas in the country are now requiring the use of DOE. The heat loss from the pipes are the difference between the DOE and the IBR. Heat loss programs are 15-20% heavy as is. If there is a problem heating when the DOE is used it is a problem in the piping not boiler sizing.


----------



## beenthere (Oct 11, 2008)

tk03 said:


> Do not use the IBR. You must use the DOE. Some of the areas in the country are now requiring the use of DOE. The heat loss from the pipes are the difference between the DOE and the IBR. Heat loss programs are 15-20% heavy as is. If there is a problem heating when the DOE is used it is a problem in the piping not boiler sizing.


Which is why you use IBR.

The same as determining the size of a hot air furnace.

If the ducts are in an unconditioned space. You add that heat loss to the load. Instead of just saying its a problem with the ducts.

DOE calculates that all jacket and pipe heat loss go to the conditioned space(too bad it doesn't work that way).

IBR calculates that all heat loss from the jacket and pipes is not loss to teh conditioned space.
Which, with the infiltration of most basements is the way it really works.


----------



## tk03 (Sep 30, 2008)

But using IBR instead of DOE and the fudge built into the heat loss programs of 15% to 20% you way oversize the appliance again. I have used DOE for about 20 years now and see many others on the Internet sites using DOE, and I have never had a problem. There is also some fudge in the IBR rating as it is a formula and not a true test. This uses some basic info which is not true to any specific application. 
I have straightened out some jobs others have done, but it was not a boiler issue. 
When I blame the piping I am blaming the near boiler piping. Would you not address that when the boiler is installed? Then the piping issues go away. That leaves flow issues. Again address that at the time of the boiler installation.


----------



## beenthere (Oct 11, 2008)

1950 era homes aren't set up with primary secondary piping.
So if their is a problem with it. Its the installer that created the problem.

If you have low flow in the pipes, doesn't matter if you use DOE or IBR, a low flow rate will hinder output.

Old steel pipes add a lot to the heat load.

Using the IBR rating allows for that additional heat loss.
Allows for proper flow through the pipes for both heating the house, and a quiet system.
Helps avoid condensation in a non condensing boiler.
Using the DOE rating can cause non condensing boilers to habe condensation, and rust out the burners or boiler due to long run times below the boilers safe min operating temperature.


----------



## tk03 (Sep 30, 2008)

> 1950 era homes aren't set up with primary secondary piping.
> So if their is a problem with it. Its the installer that created the problem.


Primary secondary has nothing to do with proper near boiler piping. I am not saying primary secondary is required. If you want it do it at the time of the installation. It is very easy to do at the near boiler piping. 


> If you have low flow in the pipes, doesn't matter if you use DOE or IBR, a low flow rate will hinder output.


Residentially the size of the pipe does not add much to heat load especially with ODR becoming more prevalent. As you reduce the temperature in the piping the heat loss from the piping is reduced.
You are right to state the difference between the IBR and DOE is piping loss and the basement is not as tight in the older homes. If that is the case this would be a waste of fuel. Insulating the pipes would make a lot of sense and still use DOE.


> Using the IBR rating allows for that additional heat loss.


Again do the heat loss and you want need the additiomnal btu's. There is plenty there is the fudge of the programs.


> It also causes to oversize the boiler.
> Helps avoid condensation in a non condensing boiler.
> Using the DOE rating can cause non condensing boilers to have condensation, and rust out the burners or boiler due to long run times below the boilers safe min operating temperature


Again this comes down to the installation and proper near boiler piping. Maybe just a bypass, circulated bypass, mixing valve or even applying any of these with primary/secondary since primary/secondary does not give boiler protection.


----------



## beenthere (Oct 11, 2008)

Bypasses are nice.

But most of them waste energy. Because your using some of the boilers heat to heat the water before it reaches the boiler(instead of heating the home). Which also causes lag in response to heat calls from the thermostat.

Insulating the pipes in some basements will get you complaints of cold floors. When that customer is use to those floors being heated by the pipes.

Using IBR, I have customers with warm floors, smiles on their faces, and low heating bills.

And no rust in the boiler or on the burners.
So the customer has a boiler that will last 30 plus years(excludes mod/cons). 


Do what you want.

No home that comes out to a 100,000 BTU heat loss, has an over sized boiler if you use the IBR rating, which would give you a min boiler input rating of 143,750BTUs(at 80% efficiency). Instead of using a smaller 125,000 input(at 80% efficiency) for the DOE rating.


----------



## Scuba_Dave (Jan 16, 2009)

I wouldn't want my basement heat pipes insulated
That would - as stated - mean colder floors
Colder floors will cool the house off faster
Insulating my rim joist & replacing the outside door & 3 single pain windows made my basement much warmer

I also had a 3' spare slantfin radiator installed in-line by the basement door (pipe & fins only). It has helped to keep my sons bedroom floor warmer


----------



## Bonnie Youngs (Jul 7, 2009)

just want you all to know that i'm listening!
B.Y.


----------



## tk03 (Sep 30, 2008)

Insulation is the cheapest thing you can put into a home. It's a one time cost that keeps giving and giving. If the floors are that cold insulate them and feel the warmth even more for a longer period of time for a rather small investment. As everyone states on the INTERNET, tighten up the home first then do a heat loss. Buy smaller operate cheaper.
Oh by the way a boiler bypass saves fuel (about 8%) not wastes it. If installed per the instruction it is cool return water into hot supply water so the heat upstairs is far more comfortable, even and cheaper to make. You get a shorter run time on the thermostat. System bypasses went out with large water volume boilers. Most manufacturers require boiler bypasses today.


----------



## Scuba_Dave (Jan 16, 2009)

I want my basement to be kept warmer
Not heated - but I'm not interested in insulating 1250 sq ft of flooring
Not to mention all the wires & plumbing I would have to weave around
And then of course if you then lose power or heat the area with your water pipes is that much colder & will freeze that much quicker

And then I lose all of that nifty storage space for my Christmas decorations between the floor joists :no:


----------



## beenthere (Oct 11, 2008)

System bypass can make the occupied area heat more evenly.
Does not always save. Seldom saves. 

Most people don't realize its not saving as much as they think. Because the bypass was installed when the new boiler was installed.

Bypass is best used to cover up/aid a bad piping job to the rads.

Or to protect a small boiler from being subjected to too cool/cold of a return water temp fro too long.

If, IF a bypass is installed, it should be done with themal bypass valve to minimize wasting fuel.
Bypass piping withouot a thermal control, are a watse, they bypass even when the water is up to temp, when it 0° outside.


----------



## tk03 (Sep 30, 2008)

I think you have your bypasses backward. A system bypass will reduce the flow to the system therefore taking longer to heat the home. Reread one of your earlier posts.You stated to reduce flow reduces output. Which is correct. If you use a system bypass some of the supply water will go from the hot supply to the cool return. That would be some gallons of water going from supply to return so it does not go into the system. Thus reduced flow in the system, reduced output.
A boiler bypass will keep the flow in the system higher thus more heat output from the radiation. The system gets only as hot as needed to heat the home. You are not heating all the gallons in the system to 180f, only high enough to satisfy the thermostat.The boiler will actually operate higher than the system water.
Boiler bypass is used to protect the boiler since the mid 50's. It was invented by a guy named Gil Carlson who worked for B&G. He did a white paper explaining the application. I quote "Flue gas condensation and thermal shock are a result of extremely cold water entering the boiler or cool water at a high flow rate". The boiler bypass allows you to slow down the flow in the boiler and allow the boiler to operate as designed and not stress or condense. The boiler water gets hotter quicker and you get hotter water entering the system water to increase the water temperature of the system. We have solved many fuel use problems with a boiler bypass. All reducing the boiler run time, system water heating up quicker. 
When the boiler is sized properly, and there is much more radiation than the heat loss, the boiler will run longer to heat up the home as there is too much cool water going through the boiler. A boiler bypass will reduce the flow in the boiler and allow you to run the boiler at any supply water temperature you want within reason. There are specific formulas to determine what delta T you adjust the boiler rise to. Once you adjust the proper flow through the boiler and size the boiler properly, this is the most efficient operation. If the flow in the boiler exceeds the rate to be less than a 20f delta T the water will take a long time to heat up. The flow should normally be between 20f to 40f. Slow the flow down in a boiler it get hotter faster.
The use of a thermal bypass valve would require a system bypass again which is going to reduce the flow in the system. I would only use the thermal bypass if I pipe the boiler with p/s piping.


----------



## beenthere (Oct 11, 2008)

A thermal bypass, will close the bypass when the boiler reaches 140°F.
So the boilers full BTU output go to the home, instead of a constant reduced flow of just a bypass.

An open (non thermal controlled) boiler bypass reduces the amount of heat going to the home at design conditions.

Often, not providing the actual GPM the boiler should have.

Check out the Burnham MPO. See how its built in thermal controlled bypass works.
Although it uses a system bypass. Its done the right way. As far as it doesn't hinder boiler performance at design conditions.


----------



## tk03 (Sep 30, 2008)

> A thermal bypass, will close the bypass when the boiler reaches 140°F


 If the boiler reaches 140f. If it is a large water volume system the return may be low for a long time.



> So the boilers full BTU output go to the home, instead of a constant reduced flow of just a bypass.


The boiler bypass always keeps the flow up in the system.


> An open (non thermal controlled) boiler bypass reduces the amount of heat going to the home at design conditions


.
The system water get to the temp that is required. The colder it gets outside the less the off time of the thermostat. So the system temperature remains higher at the call point.


> Often, not providing the actual GPM the boiler should have.


 That is where a good tech does the formula to determine flow. Once adjusted the flow in the boiler or system does not change.


> Check out the Burnham MPO. See how its built in thermal controlled bypass works.
> Although it uses a system bypass. Its done the right way. As far as it doesn't hinder boiler performance at design conditions


First off it is not thermally controlled. It is injection. 
Page 29 of the I&O manual stats this
4. The MPO is designed to withstand thermal shock 
from return water temperatures as low as 100°F, but
prolonged return temperatures of below 135°F can 
cause excessive flue gas condensation and damage 
the boiler and/or venting system.
Use a boiler bypass if the boiler is to be operated 
in a system which has a large volume or excessive 
radiation where low boiler water temperatures may 
be encountered (i.e. converted gravity circulation 
system, etc.) The bypass should be the same size as 
the supply and return lines with valves located in 
the bypass and return line as illustrated in Figures 
18A and 18B in order to regulate water flow for 
maintenance of higher boiler water temperature. 

Even the MPO wants a boiler bypass in a large water volume system.
It is backed up with the piping drawings showing a boiler bypass.
Link to Burnham MPO website manual
http://www.burnham.com/PDF/IO/MPO.pdf
So again use DOE and use boiler bypasses when needed.


----------



## beenthere (Oct 11, 2008)

I have the manual already, haven't read it for a while.
Nice boiler, installed 2. But prefer another brand.

Use IBR, and you never have excesive prolonged cold return water temps.

Using a boiler bypass. After you adjust it for proper temp rise. Your still subjsct to prolonged low return temps.

Usually means your using more circ then the system should have.

If the boiler needs/should have 1 GPM for 20° rise per 10,000 BTUs.
Why use a circ that is moving more then that(say 14GPM).
And have to have a constant bypass to keep the water flow at proper GPM(say 10 GPM).

Use a thermal bypass with a circ that is moving 10GPM, and when return water temp is up, it flows full GPM. When return water temp is low, it bypasses.


----------



## tk03 (Sep 30, 2008)

Most all of the boiler manufactures request a boiler bypass. Look it up. Weil Mclain. Buderus, Peerless etc. 


> Using a boiler bypass. After you adjust it for proper temp rise. Your still subject to prolonged low return temps.


It will but it does not matter. Cool water at a low flow rate is not a problem. Cool water at a high flow rate is a problem.
The use of a boiler bypass will increase the comfort levels tremendously. The talk of the industry today is ODR and Radiant. They both operate on low system water temperatures to elevate comfort. That is what you get with a boiler bypass.


> Use a thermal bypass with a circ that is moving 10GPM, and when return water temp is up, it flows full GPM. When return water temp is low, it bypasses.


When it is bypassing the flow (gpm) that is bypassing is deducted from the total flow. This will reduce the flow in the system and reducing flow in the system which you also have stated reduces heat output. If flow of hot water to the system is reduced than it takes longer for a large water content system to heat up and gives uneven heating. It is also trying to heat the system water to 180º or whatever the high limit is set to. As we know today with the ODR use becoming so popular and will become code in a few years on all boilers, the idea is not to heat the system water to 180º every cycle, every day. 
I guess the bottom line is if the manufactures want boiler bypass than why not pipe per the manufacturer specifications? Why reduce the flow in the system to reduce heat output?


----------



## beenthere (Oct 11, 2008)

Its a recomendation. Its not a requirement.

Bypass is seldom needed in a proper set up.

If a house only needs 10GPM, and thats what the boiler needs. No resaon for the bypass, Unless boiler is undersized. Or connected to a old gravity system with 3" pipes.


----------

