[Bonnie Youngs]

advice please: we have a 3300 sq ft house, three stories. the original boiler is from 1945, 375,000 btus. one company told me that we need two 187K btu boilers hooked up in tandem, w/o measuring the house because in the old days, engineers determined the amount of radiation from the radiators and decided the btus. thus, no new calculations need to be made. another company will measure because new boilers are more efficient, etc, etc. do either of these views seem more or less stupid? should the house be measured and determined for new btus based on new boilers and what they're capable of?

thanks in advance.

 

[qbert]

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]

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]

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

 

[Bonnie Youngs]

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]

yes remember they are not 100% efficient

 

[tk03]

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]

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]

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]

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]

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]

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

 

[Bonnie Youngs]

sorry, i see now, a cold state!

 

[tk03]

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]

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]

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]

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]

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]

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]

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