Heat loss calc to boiler output

J. Michael

Mike,
Everyone has an opinion on their prefered boiler in the size range you are looking at (100,000btu's). There looks to be enough boiler in your selection to do the heating, but you should check domestic requirements for hot water before finalizing your selection. How many showers, dishwashers,bath tubs are in the plans. Does the tub have a large flow tub filler. 100,000 net btu's with most indirects will only give you tack recovery flow rates of 3-4 gpm depending on incomming water temps and the tanks published recovery rates. Domestic requirements often are larger than the heat loss reqirements. You need to balance storage and recovery based on the actual domestic requirements. As for which type of boiler, pick one that has been in your area for at least 2-3 years and has good contractor support for design and technical issues, along with strong service and warranty support. And come on Tim, Mike is looking for sizing help, not a boiler pitch. Good luck!

andy_21

heat loss calc to boiler output

will be installing a new heating system soon, Gas fired w/ indirect 90 gal. domestic tank. I've done a heat loss takeoff w/ the Slantfin program & came up with 88K. I based the #'s on 0 degrees, LI, NY area. Now how do I match that load with a boiler. Do I use the max output #'s or the net I.B.R. #'s.
I zeroed in on the Knight condensing units, the closest in my range are the KBN 80- max output 73K net, IBR 63K
KBN 105- max output 95K net, IBR 83K

I've only spoken to 1 installer & he wants to use an even larger unit for some "cushion" do to the indirect tank. From all that I've read here it seem that the heat loss program has some room built in, I so I'm leaning toward the KBN105, Any advise would be appreciated.
Thanks

tim smith

Sizing boiler

I usually use the DOE output for sizing. Sounds like your in the right range. NOTE: my pick for boiler would be the Triangle Tube Prestige SOLO 110. Great boiler, low pressure drop on heat x, one of the highest water content heat xs available in condensing boilers for this size range. Would fit your calcs well. Good company. Good luck, Tim

tim smith

J.Michael

J.Michael, sizing help was done, not concerned about a 100mbh boiler heating domestic for this size of house load. Will provide 3gpm of straight hot water, 120 degrees with proper sized storage tank for 1st hour with a 60 gals tank, not concerned! If you look at most everybody heres post over the years, they will pretty much go along with sizing to heat load only unless special needs were brought up. Tim. Not just a pitch for my boiler of choice! Tim
You may want to watch and listen for awhile before jumping to conclusion.

andy_21

Indirect tank & boiler sizing

Thanks for the input, you mentioned no problem heating domestic water w/ a 60 gal tank. This leaves me a little concerned, we have 2 baths 1 w/ a large tub 3'x6', 5 people @ home. I was heading for a 60 gal unit, by the installer said it wouldn't handle the load, & suggested a 90 gal unit. The Knight come w/ a priority setup, would a smaller tank be ok? Or maybe a 60 gal tank w/ 180 water temp & a mixing valve for output?

But once again for the question of the hour... which #'s should I be using ,Max output or Net I.B.R.????
Thanks

tim smith

dhw load etc

Mike, as I stated, you will get appx 180 gallons of hot water, 120, in the 1st hour out of a 60 gals indirect. Thats enough to fill a 2 person large tub easily with 70% hot water out of tap at appx 5 gpm. Now if it is a 100 gallon tub w/ 10gpm fill. that would take 70 gallons of hot water in 10 minutes, figure 80% useable from tank, appx 50 gals + 30 from recovery in 10 min, 3gpmx10. Thats 80 gallons, done. Now the ??, if exact timing took place and one or 2 showers ran at the same time as filling tub w/ high volume fill, you could run low. What are the odds, that is for you to figure. Normally showers and tub use are not at the same time, evening relaxing for tub, morning showers. Showers, 5 showers in 1hr period. 3gpm shower heads, 10 min showers + 150 gallons of mixed water but only 105 gallons of hot water. Don't see an issue w/ this. PS, Use the DOE output for sizing IMOV. Tim

Tom Hopkins

indirect sizing method

Anyone have a simple indirect water heater sizing method.

Steve Ebels_3

Sizing

Been through this exercise and have a few pointers.
If boiler is indoor, DOE is fine.
For LI, NY 10 degrees is also okay. (the sizing difference is over 10%. If you use Net IBR and 0 degrees you will probably have a cushion of over 20%, bit of a waste unless DHW calls for it.

greg

Tom Hopkins

indirect sizing

Thanks Greg. I'm good with boiler sizing I guess I was looking for a simple formula for sizing the indirect based on hot water demand. Keeping in mind boiler input to achieve published ratings. I have a custom shower with 18 gpm Grohe valve plus the usual kit, washer, and 2 additional full baths. Current 60 gal. phase 3 w/ buderous oil fired not keeping up. firing rate unknown but i suspect its under fired in this case. I'm thinking close to 30 gpm peak hour usage. Which would be 1800 gal/ hr? seems like we are looking at at least 120 gallon storage.

gary disney

hot water

> Thanks Greg. I'm good with boiler sizing I guess

> I was looking for a simple formula for sizing the

> indirect based on hot water demand. Keeping in

> mind boiler input to achieve published ratings.

> I have a custom shower with 18 gpm Grohe valve

> plus the usual kit, washer, and 2 additional full

> baths. Current 60 gal. phase 3 w/ buderous oil

> fired not keeping up. firing rate unknown but i

> suspect its under fired in this case. I'm

> thinking close to 30 gpm peak hour usage. Which

> would be 1800 gal/ hr? seems like we are looking

> at at least 120 gallon storage.



well done on ur nice shower

gary disney

hot water

> Thanks Greg. I'm good with boiler sizing I guess

> I was looking for a simple formula for sizing the

> indirect based on hot water demand. Keeping in

> mind boiler input to achieve published ratings.

> I have a custom shower with 18 gpm Grohe valve

> plus the usual kit, washer, and 2 additional full

> baths. Current 60 gal. phase 3 w/ buderous oil

> fired not keeping up. firing rate unknown but i

> suspect its under fired in this case. I'm

> thinking close to 30 gpm peak hour usage. Which

> would be 1800 gal/ hr? seems like we are looking

> at at least 120 gallon storage.



> Thanks Greg. I'm good with boiler sizing I guess

> I was looking for a simple formula for sizing the

> indirect based on hot water demand. Keeping in

> mind boiler input to achieve published ratings.

> I have a custom shower with 18 gpm Grohe valve

> plus the usual kit, washer, and 2 additional full

> baths. Current 60 gal. phase 3 w/ buderous oil

> fired not keeping up. firing rate unknown but i

> suspect its under fired in this case. I'm

> thinking close to 30 gpm peak hour usage. Which

> would be 1800 gal/ hr? seems like we are looking

> at at least 120 gallon storage.



well done on ur nice shower valve, 1800 gph from 120 gallon tank impossible,u need a commercial boiler and two 120 gallon tanks with a 600.000 btu boiler.thats a lot of dead water sitting around weekly. install a everhot tankless made in watertown ma, it even says o n the label 20 gpm or what ever u want it to be and size the boiler foe 180 degree water to the unit.if u want formulas go to a engineering web site.