sizing boiler with IHW in mind

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Old 07-09-12, 10:48 AM
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sizing boiler with IHW in mind

Previously when I was sizing a new gas fired hydronic boiler (link), I came up with Burnham ES2-3 with DOE output of 59KBTUs as my boiler of choice.

My house heat loss is about 33.5KBTUs and at 180F system water temperature I have about 57KBTUs worth of fins in my heat exchangers in my house (2 zones - 2 floors). So even 59KBTUs for boiler output is more that I could possibly utilize and it was the smallest of ES2 model line.

Since my chimney seems to have a weak draft problem (link) I started to warm up to the idea of closed combustion systems and that I would need to migrate my existing 15 yo gas fired DHW boiler to IHW system eventually since right now itís using the same chimney.

So Iím trying to size up a boiler with IHW system in mind. My current DHW tank is 45G. Closest Burnham IHW tanks are 35G and 50G. I think Iíd go with 50 gallon one. The specs say that 50G tank calls for 110KBTUs of boiler output (not sure if itís DOE or I=B=R Ė anyone knows?):

see attached pic

110KBTUs is twice the size I want my boiler to be! I know that 110KBTUs for the IHW tank is not set in stone, so Iím trying to figure out what size of boiler would work in my situation. Iím looking at Burnham Revolution, ESC and PVG/SCG and series. The last two have models with 60/90/120 KBTU DOE output and revolution has models with 55/84/114 output.

The lower range models with output of 55 and 60 are too small. But Iím wondering if I should be ok with 90/84 output. If anyone has some thoughts to share on this, I would really appreciate it!

edit: after some reading i think i will be ok with 35G tank with a mix valve installed just in case i'm wrong and need a bit more hot water...
 
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Old 07-09-12, 02:57 PM
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You size your boiler to your heat loss. You do not need a larger one for IHW. What you want to do is have the IHW on priority. So when the tank calls for heat, it shuts down your heating zones until the hot water call is satisfied. The boiler size ratings for the IWH are what they used to get the first hour ratings. You can use a smaller boiler, but the first hour rating will be less.
 
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Old 07-09-12, 04:30 PM
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but the first hour rating will be less.
And if you do manage to draw all the hot water from the tank, the recovery time will be slightly longer.

True that you won't meet the 'published maximum best case' spec, but I don't think you will have any problem adjusting your habits, and in fact you may not have to anyway. Chances are pretty good that the boiler/indirect combo even with the smaller boiler will be at least equal to, if not better than, what you have now.

a mix valve installed just in case i'm wrong and need a bit more hot water...
That's not the only reason for a mixing valve. The primary reason is for SAFETY. Anything over 125į water at the taps runs a risk of scalding, particularly for the young and the elderly. The fact that it 'extends' the hot water supply is a happy side-effect.
 
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Old 07-09-12, 06:32 PM
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That's not the only reason for a mixing valve. The primary reason is for SAFETY. Anything over 125į water at the taps runs a risk of scalding, particularly for the young and the elderly. The fact that it 'extends' the hot water supply is a happy side-effect.
AND it kills any legionella bacteria .
 

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Old 07-10-12, 05:59 AM
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AND it kills any legionella bacteria .
Yes, should have mentioned that also. To do so requires that the water heater temp be maintained at 140įF .

Google " Legionella " for much more information on this.
 
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Old 07-10-12, 07:16 AM
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guys, thanks for your answers. i actually checked our current tank and it's 40g, not 45, so indirect 35g should be sufficient. we never come close to draw the entire tank and from what i read on this forum IHW "runs" bigger. my only concern is my 20 months old daughter. i hope the IHW tank lasts forever so there will be point where my daughter will become the biggest consumer of the hot water

well, with all that in mind, does it mean that i can consider 60KBTU DOE output for my application? it sounds like it should be fine.

i have 2 follow up questions..

1. "cold start"

it was mentioned several times on these forums that the boiler "should be converted to cold start". i also found a small explanation from NJ Trooper (I'm glad you chimed in on this thread):

Also, understand that unless you change your aquastat, you will still have what is called a WARM START boiler, meaning that it maintains temperature. This costs you $$$.

BUT, SOMETIMES a boiler that has spent it's life as a warm start will not like going cold. It will start to 'weep' (leak) because the iron will contract.

If you change out the aquastat to an L7224U , you will have the ability to turn the LOW LIMIT warm start function on and off. If you find that it does not leak when it goes cold, then leave the low limit off... if it leaks, turn it back on to a minimum temp... say 120 or so.

Read more: http://www.doityourself.com/forum/bo...#ixzz209nsixkX
as far as i understand this, by default the boiler (some boilers?) will hold the temperature above specific threshold (what's the number?) even if there is no call for heat. replacing aquastat will let one to override this function. my 30 yo old boiler falls back to ambient temperature when there is no call for heat. at least i believe it does so. maybe because it's too old and newer ones stay warm?

right now i'm thinking about burnham scg3(4) boiler. it seems that majority of burnham boilers are designed with IHW in mind, so i wander if it's a cold start boiler to begin with or will i have to do some extra work to convert it?

2. what is preferred way to pipe IHW - with a zone valve or dedicated circulator? what are the pros and cons?
 
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Old 07-10-12, 07:58 PM
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Indirects are sized off the DOE output to achieve maximum specified numbers. What are your hw demands. A 25 gallon tank may do the job. Please take the time to compare the numbers and you will see what I mean. Are eight gallons that important to you?
All gas boilers today are designed as cold start.
Zone valves for heating is great but I prefer pumps for the indirect over zone valves. Will it work OK with a zone valve on the IWH? Yes, but the zone valve should be full port which is hard to find. The new ESC, ES2 and Series 3 will be able to have two inputs and control two pumps. That means you can run a pump on the indirect and a seperate pump with zone valves for heating with priority for the indirect. It will also include pump prepurge which is a nice feature fo up to a 10% fuel savings. Then add the plug in ODR module for an added savings of up to 15% - 20% more.
 
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Old 07-11-12, 07:42 AM
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rbeck,

Thanks for your input, I appreciate you taking time to respond. Right not our hw demand is low, our family is 2 adults and 20 month yo. It will increase in the future so Iím trying to plan for that. I think 25 gallon tank might be big enough, but both 27g and 35g alliance sl tanks are rated for 99mbh boiler output and 35g tank is actually cheaper on pexsupply, so I see little harm going 35g.

Do you think 60mbh doe output boiler (scg3) is big enough for 33.5mbh heat loss, 52mbh emitters (I know this is irrelevant for sizing, but just for reference), ihw rated at 99 mbh boiler output for maximum numbers? The math seems to say yes, but I just wanted a second opinion from pros here in case Iím missing something.

Regarding cold start, if all of them designed for cold start, why is it referenced several times on this forum about converting to cold start? Not arguing with you, just curious.

I looked at Burnham boilers as a brand of choice. I really like ES2-3 boiler. But it looks like in my air tight house I might be better off with sealed combustion boilers. So it narrowed it down to revolution, esc and pvg/scg models.

My gas bill is relatively small. On the coldest months itís about $175, excluding DHW and cooking. My calculations tell me that I will not recoup the investment in mod/con boiler and that does not even include possible extras for maintenance. So I want to go with a simple but efficient boiler. Either of revolution, esc or pvg/scg seem to fit the bill, but pvg/scg is $400-$600 cheaper. Does revolution or esc have any big advantages over pvg/scg that should tip the scale towards them?

ESC has IQ system that would allow for ODR reset that you mentioned. With LCD display and IQ ODR card ESC will take about 10 years to break even compared with a simpler PVG/SCG boiler. That if I realize 15% fuel saving. However I was under impression that ODR works the best with con/mod boilers by bringing the system to condensing temp and getting extra 10% from latent heat extracted from flue gases. So Iím a bit skeptical about 15% savings with ODR. But to be honest a software engineer in me wants to have an ODR rest card and LCD display to monitor the system and tinker with it .

Revolution is slightly more efficient, but I donít think the price justifies the difference in efficiency. Otherwise I donít see differences with PVG/SCG.

And what is pump prepurge and how does it work?
 
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Old 07-11-12, 03:33 PM
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If you are concerned about paybacks, skip the LCD. You can do the settings for the boiler just fine without it. There is a small 3 digit lcd on the control board. I have an ES2 with the 35 gallon Alliance. My boiler is the 105k input and I like it. My indirect is piped with a zone valve. I also have the add on ODR and low water cut off.
 
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Old 07-11-12, 03:51 PM
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Regarding cold start, if all of them designed for cold start, why is it referenced several times on this forum about converting to cold start? Not arguing with you, just curious.
Older boilers that used the internal tankless coils for domestic HW are mostly the ones we are talking about converting. Folks will abandon the tankless coil in favor of either a stand-alone WH or an indirect, with no thought to converting the boiler to cold start. Contractors often don't mention it because they don't really care about your fuel bills and it adds $ to the bottom line of the contract. Let's face it, it's easier to sell for lower bottom line!

ODR will benefit a conventional boiler just fine... it's not just for mod/cons. Anytime you can heat your home with cooler water you are saving.

I agree... skip the fancy display. It doesn't add any functionality, it's just a bell and a whistle.
 
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Old 07-11-12, 06:42 PM
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35g tank is actually cheaper on pexsupply, so I see little harm going 35g.
Strange as the price from US Boiler is higher for the 35 gal tank by about $40.

Do you think 60mbh doe output boiler (scg3) is big enough for 33.5mbh heat loss, 52mbh emitters (I know this is irrelevant for sizing, but just for reference), ihw rated at 99 mbh boiler output for maximum numbers?
I think you already he you answer. Is the boiler the same size or larger than the heat loss? The IWH will not meet the spec's for the first hour rating but you won't need it. I had a family of four and a 20 gallon tank (not Alliance) and never ran out of hot water. A single bathroom will be OK with he 27 or 35 gal tank. Many people think it is always better to have a larger tank which may actually supply less hot water due to restricted input. Many times a smaller tank will recover faster. This is not the case with the 27 or 35 tank as they have the same input and output ratings.

I looked at Burnham boilers as a brand of choice. I really like ES2-3 boiler. But it looks like in my air tight house I might be better off with sealed combustion boilers. So it narrowed it down to revolution, esc and pvg/scg models.
I agree with this idea, why pull heated air from the home for combustion. The SCG is being discontinued and the PVG is indoor air only. You may still find some SCG's in inventory somewhere.

With LCD display and IQ ODR card ESC will take about 10 years to break even compared with a simpler PVG/SCG boiler.
For the home owner I would agree that the display is bells and whistle. For the service tech it is a good tool. It rthes history tha is not displayed on the little screen and also reads the flame signal. It does make the set-up of the controls easier.
The ODR normally recovers cost in about three to four years.

And what is pump prepurge and how does it work?
See the link below.
Advantages of circulator pre-purge
 
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Old 07-12-12, 07:26 AM
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drooplug:
I also have the add on ODR and low water cut off.
i see several IQ cards that are available for burnham boilers: ODR, LWCO and external limit (aquastat).

the ODR is obvious - it provides new functionality that the boiler simply doesn't have.

External limit - it looks simply like an additional aquastat that is fancier than a standard. from what i can find it has "built-in diagnostics" and may be required by some local codes, but otherwise it does absolutely the same. why would one want it?

LWCO - i understand it's function, but i'm curious how other boilers get along without it? if one runs the boiler with intake loop open, then there is a danger that if leak develops it would result in a lot of water in the house. if intake is closed and there is a leak then the boiler can go dry and that's the situation when LWCO will save the day, right?
 
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Old 07-12-12, 07:30 AM
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NJTrooper:
ODR will benefit a conventional boiler just fine... it's not just for mod/cons. Anytime you can heat your home with cooler water you are saving.
i agree, i just don't think it will be advertised 15-20% savings, but rather below 5%. as a matter of fact, all of the people in this thread (except TOHeating) discussed this very subject in the thread i started 8 months ago:

http://www.doityourself.com/forum/bo...efficeint.html

 
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Old 07-12-12, 07:37 AM
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rbeck,

35g tank is actually cheaper on pexsupply, so I see little harm going 35g.
Strange as the price from US Boiler is higher for the 35 gal tank by about $40.
i don't see any prices on usboiler.com, is that's the site you're looking at? at pexsupply 27g is $905 and 35g is $898: PEX - Radiant Heat - Radiant Heating - Plumbing Supplies - PexSupply.com

doesn't make much sense though.

The SCG is being discontinued and the PVG is indoor air only. You may still find some SCG's in inventory somewhere.
that's good to know, i didn't realize that SCG are being discontinued! i did notice that only few sites actually sell them. it's strange though that they don't phase out power vents first. if that's the case, by the time i might need a boiler, there might be no choice, but ESC for me!

thanks for the link for pre-purge!
 
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Old 07-12-12, 07:50 AM
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guys, thanks a lot for your help!

with your help in my other thread (http://www.doityourself.com/forum/bo...ey-lining.html) i came to a conclusion about going closed combustion with IHW.

at this point if i had to replace my boiler i would try to find SCG3, but by the time i really need it, it might not be available and then i would go with ESC3. i'm not sold on ODR just yet, but it will be nice to have as an option if i change my mind. i might ask for it as my birthday gift from my wife (i like practical gifts )

now it's just a matter of timing - i have 32 yo boiler and 15 yo HW heater. both atmospheric. if boiler goes first it's a no brainer - i get new boiler with IHW and toss the existing HW heater.

if HW heater goes first, then i might be tempted to get another heater like this (less then $300 shipped):

Amazon.com: Rheem 22V40F1 Natural Gas Water Heater, 40 Gallon: Home Improvement for time being.

it would be nice if i could keep an atmospheric HW heater and sealed combustion boiler, i'd like to have heat and hot water separate for simplicity and redundancy. i love the price of a stand alone HW heater comapred with IHW. however this combo doesn't make sense.

thanks again for all your help, i feel prepared now
 
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Old 07-12-12, 02:48 PM
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If your hot water heater goes first, you can add an indirect water heater to your existing boiler.

The LWCO is there to stop your house from burning down if your boiler loses all of its water. Many local codes require one these days.
 
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Old 07-12-12, 07:29 PM
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Chimney vented stand alone water heaters make no sense what-so-ever. When an appliance is connected to the chimney, the chimney constantly sucks heat from the appliance and also heat from the home 24/7 via the access door and draft hood. The hotter the water in the tank the more heat that gets sucked out by the chimney.
I would rather not pay the fuel to heat water that is cooled by my chimney.
As far as ODR there may be a few manufacturers utilizing it to meet the new 2012 codes coming Sept 1st. Don't know what they all are doing yet.
You will not see pricing on US Boiler website as they do not sell over the internet. I have a nprice bookook :~) and know they will be discontinuing a few model lines due to 2012 compliance.
 
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Old 07-13-12, 07:53 AM
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drooplug, it is an option to pair IHW with my current boiler. unfortunately it's a bit more complicated to do DIY, so i would probably hire someone to do it. the cost of installation would be easily twice the price of new regular HW heater, which is very easy to install and i could do it myself.

rbeck, i was thinking about it as a temporary solution until i need to replace the boiler. right now i have both atmospheric vented boiler and HW heater. if heater goes south i could replace it with the same type and then when boiler gives up, go sealed combustion boiler with IHW.

does anyone know what happened to "quote" button at the bottom of every post? for some reason i only have "reply" button.
 
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Old 07-13-12, 02:42 PM
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They got rid of the quote button. I don't agree with their decision. You have copy and past you text and use the little quote icon when replying to threads.

The alliance tank will last forever. You will have to pay to have it installed whether or not it is done with a new boiler.
 
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Old 07-13-12, 03:36 PM
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yeah, the quote button was very convenient!

as for ihw tank installation - i would pay for it twice if i go with the my original boiler first and then with the replacement boiler
 
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Old 07-13-12, 04:10 PM
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yeah, the quote button was very convenient!
I
didn't
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gone!
Although, it doesn't really make sense to quote an entire reply... I usually do the cut and paste trick.
 
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