Measuring EDR

Paul_11

Brad, you are so right, so let's see the calculations.

I already gave the HO mine and I'll give them to you too, if you contact me off wall. If I could attach them here, I would.

I am the contractor who is suggesting nothing bigger than 349,000 BTU. As you will see, if you dig into this post, I would like to go even smaller.

What the HO didn't tell you is that all three contractors post to the wall, but I don't know who the other two are.

I do have a question though, that I would ask them and all of us, if the existing boiler has 362,000 BTU input and many tenants complain about being too hot, why make the new boiler bigger?

As Emerald says, let's kick this up a notch and while we're at it, let's look critically at our understanding of how to use our connected load calculations.

Recently I contacted Dave Yates, off wall, to ask him what his thinking was about a critical aspect of this job. How do we use our connected load calculations? Dave suggested that I post it to the wall, so we could all dig into this question. I will do so here, where it is most relevant.

DAVE,
I just finished reading your article in the February 2007 issue of Contractor. It was a great article and sounds like a nice job. But one sentence stimulated my thinking. On page 26 you say," Steam systems must be sized to produce enough steam to completely fill the inside void of all radiators and piping connected to the boiler, which is referred to as connected load." Just so you know, I am very aware of the importance of doing a connected load calculation, and I am familiar with actually doing connected load calculations. I have been doing them for many years.

But lately I have been thinking about one aspect of what you said. Why do we have to fill the radiators with steam if they don't need to be full to provide enough heat to the space involved? One part of the thinking behind using a Tekmar 269 or Heat timer control to change the length of the heating cycle is to be able to adjust the amount of steam we send to the radiators. Depending on the outdoor temperature, we only provide enough heat to replace the heat loss. When we do this in the shoulder seasons, the entire radiator doesn't get hot. The entire radiator only gets hot when it needs to, because it is colder outside.

I do agree that we always have to be able to fill the steam supply piping with steam or we won't get the steam to the radiators. But I have had situations where the actual connected load is more than what is actually needed to heat the building. As long as I size my boiler to always fill the steam piping with steam and have enough left over to provide enough steam to the radiators to heat the building on the coldest day of the year, my system works. However, I may not be able to completely fill the radiators with steam on the coldest day of the year.

I am currently preparing a contract for a job where the connected load says we need a 362,000 BTU boiler, but a very rough, but conservative heat loss shows a lot less BTU requirement. It is only a 4400 square foot building. It has 1100 on each floor, with one side attached, so only three sides are exposed. Other buildings are close, so wind is not really a factor. Many tenants have at least one radiator turned off already, some have two. I could remove some radiators, but why can't I just leave them installed and not fill them up completely.

The sad part of this is that I can't get away from the fact that I have to be able to heat the supply piping. But, if I get the job, I do plan on installing a boiler sized somewhere between 300,000 BTU and 330,000 BTU.

What do you think about this question of not always having to fill the radiators with steam?

Paul Shay

Anyone who wants the charts I prepared or the critical part of the contract where I analyze them, contact me off line.

Let er rip!!!!


Respectfully,

Paul B. Shay
pshay@arealgoodplumber.com
LMP 1307
LMFS 654B
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EF_3

Measuring EDR

I live in a four family building, and we need to replace our gas powered steam boiler. Problem is that we get different opinions about the size of the boiler we need. One contractor says we could use a boiler with 349 MBH input, another recommends the next size up at 385 MBH, and another recommended 450 MBH.

I understand that the boiler size depends on the square footage of radiant heat. What do I do if everyone's meansurements are different? And how do I know that they are correctly calculating for heating the pipes that feed the radiators?

Brad White_9

Ask each of them

for their assumptions and calculations if they are willing.

I can understand some reluctance should they think you are going to "shop out" their intellectual property. But if you assure each that you want to know their basis and will not give the information out to others, I cannot see why they would not share it.

Remember, you in the end will live with the results for the life of the system.

mel rowe

Paul, I read your post and just wanted to pass on some info, FWIW. I'm a HO with a one pipe steam system in an old house. The house is free standing and I live in southeastern Mich. I learned a lot from the Wall and have done a lot on my own system. The place you brought up sounds a lot like the size of my place. I had to have a new boiler installed when I moved in 19 years ago. It is a Utica 300k unit (too big, I have since learned, for my needs). The connected EDR I calculated as 612. I have downfired the boiler to fit the attached load. Since I have added thermal windows, wall foam insulation and foam in the attic, the rads are really too big, but of course I don't plan to change them. I have added a number of TRV's to gain better temp control, which also might be a consideration for your quote on the job. The end result is as you mentioned, a lot of the rads do not get completely hot, but the room temp is fine. The thing that I thought might be of some interest to you is that the downfired output of my boiler is about 232K, with a 4000 sq. ft. house, and the boiler only has to run about 40% of the time, on the coldest days. So it seems to me that you are on very conservative ground with your proposed smaller boiler capacity.