Now Which size boiler?
#1
10-12-08, 06:47 AM
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Now Which size boiler?
Okay, I've done my homework and my heat loss calculations. I want the Buderus g125be. I have a 1960's 3K sq foot colonial in CT with new windows. My heat loss calculations (from pprbd.org) results in:
"Building envelope Heat loss = 23,750 BTU/HR
Infiltration heat loss = 10,600 BTU/HR
Total Heat Loss = 34,350 BTU/HR
- the calculator totals 2500 sq ft, which is 500 less than what I figure I had- I assume this is due to closets, and interior dimentions rahter than exterior. I also did not bother to include the basement/garage- as this is not formally heated space.
The contractor sudgets the G125BE/34 size boiler. I have 3 zones, and are going with an indirect water heater (they say weil mclain plus 40 - with 4 people in house)
How do I figure out what size boiler I need, and if he is correct or oversizing me?
"Building envelope Heat loss = 23,750 BTU/HR
Infiltration heat loss = 10,600 BTU/HR
Total Heat Loss = 34,350 BTU/HR
- the calculator totals 2500 sq ft, which is 500 less than what I figure I had- I assume this is due to closets, and interior dimentions rahter than exterior. I also did not bother to include the basement/garage- as this is not formally heated space.
The contractor sudgets the G125BE/34 size boiler. I have 3 zones, and are going with an indirect water heater (they say weil mclain plus 40 - with 4 people in house)
How do I figure out what size boiler I need, and if he is correct or oversizing me?
#2
10-12-08, 07:57 AM
34K sounds a bit on the low side to me ... I haven't seen the calculator you used on-line... I'll check it out later.
However, your home's heat loss is going to likely be lower than the indirect is going to require, so you will be sizing the boiler for the indirect. Keep in mind that you _can_ compromise _somewhat_ from the factory recommendations for the requirement on the indirect. All that will happen is that you will not meet the full recovery time spec and first hour draw on the indirect... in other words, how much you compromise on the requirement for the indirect means you might have to wait a few minutes before your third shower, or load of wash.
So, yes, the boiler will likely be oversized for your heat loss, but undersized for the indirect full specs... depends on how much you (or the contractor) are willing to compromise on indirect performance.
I'll be Xiphias can run the numbers for ya... he's good at that ... or did he already ?
However, your home's heat loss is going to likely be lower than the indirect is going to require, so you will be sizing the boiler for the indirect. Keep in mind that you _can_ compromise _somewhat_ from the factory recommendations for the requirement on the indirect. All that will happen is that you will not meet the full recovery time spec and first hour draw on the indirect... in other words, how much you compromise on the requirement for the indirect means you might have to wait a few minutes before your third shower, or load of wash.
So, yes, the boiler will likely be oversized for your heat loss, but undersized for the indirect full specs... depends on how much you (or the contractor) are willing to compromise on indirect performance.
I'll be Xiphias can run the numbers for ya... he's good at that ... or did he already ?
#3
10-12-08, 09:31 AM
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No, I did the calculations. I'd post the excel spreadsheet- but I don't know how. I can post the figues here if it will help- but I think your right- that the water tank - if that is the right size, is the greater of the heating need. Now were 2 adults, and 2 kids- but it is aa 4 bedroom house- So I figure sizing accordingly- as if I am able to continue to feed them, ultimately they will grow The difference is the Buderus and weil mclain indirects is buderus is about $350 more - so I was going cheaper- but that was based upon the plus 40.Anyhting else I should consider? Otherwise I'll sign the deal later this week.
#4
10-12-08, 10:09 AM
Since when do you size an indirect on the number of people in the home. If you have one full bath, and a clothes washer the amount of people don't matter. One full bath normally means one person in the shower at a time. It don't matter if there is one person or 12 people in the home it is still one full bath. This si just the next thing which becomes oversized after the boilers. When I was a service manager we installed hundreds of indirects. They were all 20 gallon tanks except maybe 20-30 of them. Look at the load not the amount of people. Too large of a tank will take longer to recover and even supply less hot water most of the time. I have done many tank size comparisons and have proven a smaller tank (correct size) will supply more first hour rating hot water, more often (back to back showers) and less recovery time than a larger than required tank.
#5
10-12-08, 05:09 PM
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I have 2.5 baths, clothes & dish washer, and no need to oversize. I could potentially see 2 shoers at once, when they kids get older. We also have very strong water pressure- so we can use a significant amount of water if we try- for example- now with our coil, I can not turn on the Hot water full blast, or I'll end up with a tub full of cold water.
So how do I size an indirect then??? How do I figure out how many gallonss I am using when I shower- which is what all the ratings are based upon, correct? When I had 3 initial quotes last year- 2 were for 40 gal units, but one was 80- which I knew was way over.
So how do I size an indirect then??? How do I figure out how many gallonss I am using when I shower- which is what all the ratings are based upon, correct? When I had 3 initial quotes last year- 2 were for 40 gal units, but one was 80- which I knew was way over.
#6
10-14-08, 01:47 PM
Even after a whole heck of a lot of reading and researching, and playing with numbers, I still don't exactly get the sizing of indirects. The manufacturers don't help much either, as most base their ratings on whatever 'standard' makes theirs look best.
There are a few recent threads around here about games you can play with indirect sizing, adding a tempering valve, providing them with a large boiler to match manufacturer specs, or not, etc. See if you can find them, and post back with more questions.
There are a few recent threads around here about games you can play with indirect sizing, adding a tempering valve, providing them with a large boiler to match manufacturer specs, or not, etc. See if you can find them, and post back with more questions.
#7
10-14-08, 03:25 PM
Here is what I have used for some time with different manufacturers as long as they have a coil in them. never used it on a tank in a tank.
http://www.comfort-calc.net/tech_area_index.htm click on sizing residential indirects under the water heading
http://www.comfort-calc.net/tech_area_index.htm click on sizing residential indirects under the water heading
#8
10-14-08, 06:10 PM
your boiler size sounds way to small for a 3,000 sq ft home you should probably be up around 120,000btu output and as far as your indirect the style you want will work with a 40 or 50 gallon tank as long as it is installed properly (correct pipe and pump size)
#9
10-14-08, 06:37 PM
plumboy, 40 BTU/SF ? too much ... unless there's a wall missing somewhere... certainly not more than 30 BTU/SF, and probably less, perhaps much less... depending on how well insulated, condition of doors/windows, etc.
How did you arrive at 120K ?
If I put 120K in this place, it would be 2X oversized for 2000 SF.
How did you arrive at 120K ?
If I put 120K in this place, it would be 2X oversized for 2000 SF.
#10
10-14-08, 06:49 PM
I just went to that pprbd link ... Pikes Peak Regional Building District... I think that's very cool that they care enough about wasting energy to actually put the Manual J forms AND an excel spreadsheet up on the website. I'd almost be willing to bet they won't grant a permit without a heat loss calculation. Bravo!
Moose, why not download the software from slantfin and give that a go... I'd be curious to see how it might differ from your standard Manual J ?
Moose, why not download the software from slantfin and give that a go... I'd be curious to see how it might differ from your standard Manual J ?
#11
10-14-08, 06:55 PM
he said the house is 3000sq ft not 2000 sq ft unless i am reading his post wrong. if it is 3000 sq ft you are coming up with roughly 90,000btu and i am coming up with roughly 120,000btu. I would say we are both pretty close considering we have never seen the house.
#12
10-14-08, 07:04 PM
I said THIS place is 2000 sf ... yes, he did say his was 3000 ... but then said his manual J came out to 2500 ...
Point being that if his heat loss is 90K, 120K is still too big, and I'm willing to bet the farm his is not more than 75K ...
Point being that if his heat loss is 90K, 120K is still too big, and I'm willing to bet the farm his is not more than 75K ...
#16
10-15-08, 06:46 PM
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Thanks for all the attention. I looked a rbeck's web sites, and come up with about 144 for peek demand- but I assume this figues in taking a shower, doing laundry, dishes, and maybe a bath all at the same time? Can that be right- I mean, do people really figure out HW this way? I've always been one to turn off the washer when I take a shower. So I figure either a 30 or 40 gal size will do- and I'm probably somewhere in the middle, so I will probably go with the 40 so I don't have to hear it from the others in the home.
Yes its a 3k sqft home, that figures into the 2500 during the calcs. NJT- I'll see if I get to the slantfin software and give you the results for some kicks - but I'm still recovering from a lead contamination here and trying to get all this done- but maybe a slow day at work- since I already did all the measures. I'll let you know.
Beer 4U2
Yes its a 3k sqft home, that figures into the 2500 during the calcs. NJT- I'll see if I get to the slantfin software and give you the results for some kicks - but I'm still recovering from a lead contamination here and trying to get all this done- but maybe a slow day at work- since I already did all the measures. I'll let you know.
Beer 4U2
