BTU Ratings

Hi all. I got a queston about BTU ratings. For example lets say that my house heat loss is 198000 BTU's. So then I buy a boiler that has this rating. Like this one.

http://www.alpinehomeair.com/viewproduct.cfm/productID/453056107/p/Burnham_207NCL_TEI2

If you scroll down on this page you will see that the heating capacity is 198000 BTU. The effective heating capacity is 163000 BTU's and the net water rating is 142000 BTU's. When buying a boiler which one of these ratings do you go by?

 

The 198K is input. If your heat loss is 198K, this boiler would certainly be too small. Here is a link to some information on Burnhams web site. I suggest you go there to learn more about ratings. http://www.burnham.com/ratings/2b.cfm

 

What kind of building do you live in, and in what climate, that has a design heat loss of 198,000 BTU/hr? That's huge. How much and what kind of radiation (baseboard, radiators, etc.) do you have?

 

I was just using the 198000 BTU as an example. I'm pretty much settled on that model boiler. I was just wondering why they rate BTU's different like that. My house heat loss is almost done. Right now it stands at 107K. That is without the garage that eventually I want to heat.

 

With I=B=R ratings, they presume any heat loss thru the jacket & piping (other than emitters) is lost & not going into the house. Dept. of Energy ratings presume such loss is actually going into heating the structure so it is not actually lost. A lot depends on where the boiler is located. If, for example, the boiler were in a detached building & piped underground, the I=B=R rating would be the one most applicable. On the other hand, if the boiler were in an open area of the basement where jacket loss could be used to heat or partially heat said basement, the DOE rating would be more accurate.

 

jetmx, what kind of boiler are you thinking of getting>

have you done a secondary check of your heatloss based on consumption using your current setup?

heatlosses can be vastly overstated - my 55k is actually probably a bit less than 40k - if i did my heatloss and increased height to account for joist spaces it would be even further out...

 

Thanks for the link to Burnams site Grady. I am going to read it more in depth soon. I am having a plumber who is a friend of mine do the heat loss calc. He isnt done yet. Not too long ago I had another plumber estimate without doing the heat loss. He said if I wanted to heat the garage and install an indirect water heater that it would be around 170000 BTU's. The boiler I have now is a dinosaur (National-U.S. All fuels boiler). It actually has ratings on a placard for wood, steam, gas, and oil. The only thing that I know about it is that it has been converted from oil to gas. It is original with this house that was built in 1960. It is located in the basement. I am going to get the Burnam series 2 boiler when I know what size I need. I have to wait until the calcs are finished. I have read that the 50 gal alliance indirect water heater requires a 164000 BTU boiler. After reading some about indirects I take it that the 164K would be required if there was not priority. I have a zone valve controller that has the priority option. If I use the priority, from what I understand I can use a smaller boiler that is more tailored to heat loss. Am I on the right track here? I trust my plumber, I am confident that he will set me up with the right equipment. I just like to know as much as I can about home projects.

 

164K for an indirect? Must be almost instant recovery or you are flowing an awful lot of hot water. I did not see any flow requirements for the boiler water but did notice that the connections are 3/4". Unless they are really ripping water thru that coil, I don't see how you are going to get 164K into that indirect. Here's a link to the installation & service manual for the Alliance water heaters:
http://www.burnham.com/pdfs/CurrentPDFfiles/Alliance%20SL%20Manual%2011-06_new.pdf

 

Here is where I have read that the alliance 53 gal water tank needs 164K.

http://www.burnham.com/ratings/all.cfm

I am still gathering lots of info about whats needed for my house. Nothing is final yet. I'm just trying to get a good perspective on what is exactly needed.

 

I see the ratings & requirements. Eleven gpm is a lot of flow. You might want to look at the Taco or Grundfos web site to determine what circulator you would need. If you were thinking of using a zone valve, don't. I also noticed the flow out of the tank was rated at 5 gpm, 140º, & 9 minutes. That is a lot of HOT water. No way are you going to want 140º out of the shower. I have a Crown 26 gallon indirect & we can get two showers back to back before running cool. If 10 minutes is allowed between showers, any number of showers can be taken without problem. My boiler has an IBR net of 80K & the domestic is not on priority. Not sure of DOE rating. Once the heat loss is done for the house, post back in this same thread & we can talk more about indirect & boiler.

 

There was a discussion about this in another forum recently.

One comparison was to a typical electric water heater.

One KWH of electricity is appx 3400 BTU. Typical EWH would have a 4.5 KW element (yes there are two elements, but they don't operate simultaneously).
So, a typical EWH uses appx 15,000 BTUH to do the job. Sure the recovery time is pretty poor, but it does (eventually) do the job.

By running the indirect with less BTU, all that suffers is the recovery time. You just end up heating the water more slowly than the MAX rating of the heater.

Something doesn't quite add up though.

First, if the required flow for MAX perf is 11 GPM, then that's only 110,000 BTU based on a 20* delta T .

Second, to flow 11 GPM through 3/4" pipe seems crazy. I know that in heating apps the flow for 3/4 is usually max of say 5 GPM (usually less). Potable applications go as high as 8 GPM, maybe a bit more.

puzzle pieces missing...

 

I probably won't get the indirect until next year. But I'm curious. Why not use a zone valve? I'm currently using a zone valve controller for 2 zones. It would be easy to add another valve on the manifold. But I also have a switching relay and it also would be easy to add another circulator for the indirect. I definetly will post back when the heat loss calc is done. Probably Tue.

 

Grady was probably concerned that you would have trouble getting the required flow through a zone valve...

 

My two cents. First issue with a ZV is the delay. A Taco 571, for example, takes about 90 sec to open after getting the call for heat. At 2.5 gpm (typical showerhead), that's almost 4 gal gone before the valve opens (10% of a 40gal tank...). Yes, there are other zone valves that do not have this issue. Add to this whatever time delay is involved in an atmospheric boiler (vent damper opening) to get it going. Second issue is the flow. Depending on what indirect, what boiler, how it's piped, etc., you might not achieve the required flow rate for the indirect. Third issue is that some control packages won't let you put a zone valved indirect on priority. Most or possibly all of the tekmar controls would be an example. A Taco ZVC, however, does allow zone valve priority.

I have one data point. My indirect (State Systems, plain-Jane, 40 gal smooth 3/4" coil) used to have a zone valve, Taco 007 system circ, and a 164k BTU input (Burnham 206) boiler. No priority. It would take the boiler several minutes before it would start doing any real work. Recovery times were pretty long just due to the amount of work that needed to be done. Lots of cold water to heat up.

Same indirect now has a dedicated 007 on priority, and a boiler half the size. Much, much better performance. Essentially no delay between the indirect's stat call for heat and when the system gets to work.