Need help with a heat exchanger for Pellet Boiler

[Patti]

Hi,
I am in the process of installing a wood pellet boiler in my shop that will heat my house and shop. I have just started looking for heat exchangers (water to air) on ebay and I need to know what size of heat exchanger I need for my system.
I will give you a bunch of information (some of the info probably won't be any use to you, but I'll include it anyways, just in case!) and I hope you can help me with some questions...

-The pellet boiler is a Woodpecker 25kW (which, I think translates to approximately 85360 BTU's??? Is that correct?)
-I have a 600 gallon insulated stainless steel storage tank that will store water in the shop (but I can add more water storage if necessary).
-I have a new electric water heater for the house, and will be getting some additional water storage containers for the house soon.
-We've installed about 110 feet of Pex tubing from the shop to the house.
-The pellet boiler is going to be used to heat my domestic hot water, forced air heating, the in-floor radiant heating in the kitchen, a hot tub (inside the house), a 16' x 24' pool, and the shop.
-I would like to run central air in the summer as well
-The shop is an insulated steel building, 40 x 50, but it won't be heated above 60 degrees.
- The house is 2500 sq feet (not counting the basement of course).
-One and 1/2 storey 1857 log cabin.
-New roof and spray insulation
-Windows need to be replaced, so I currently lose a lot of heat there
-The duct work might need some additions, and more return air ducts added
I assume that I need two heat exchangers- one for the shop and one for the house?
What size would you recommend for each building?
I want to be WARM!! I live in the snowbelt in Ontario, Canada and we have brutal winters, so I want to make sure that whatever I use in the heating system is going to be large enough to make sure I stay warm * happy

Any help or information you can give me would really be appreciated!
Thanks.
Patti

 

[Bob Rohr]

Hi,
I am in the process of installing a wood pellet boiler in my shop that will heat my house and shop. I have just started looking for heat exchangers (water to air) on ebay and I need to know what size of heat exchanger I need for my system.
I will give you a bunch of information (some of the info probably won't be any use to you, but I'll include it anyways, just in case!) and I hope you can help me with some questions...

-The pellet boiler is a Woodpecker 25kW (which, I think translates to approximately 85360 BTU's??? Is that correct?)
-I have a 600 gallon insulated stainless steel storage tank that will store water in the shop (but I can add more water storage if necessary).
-I have a new electric water heater for the house, and will be getting some additional water storage containers for the house soon.
-We've installed about 110 feet of Pex tubing from the shop to the house.
-The pellet boiler is going to be used to heat my domestic hot water, forced air heating, the in-floor radiant heating in the kitchen, a hot tub (inside the house), a 16' x 24' pool, and the shop.
-I would like to run central air in the summer as well
-The shop is an insulated steel building, 40 x 50, but it won't be heated above 60 degrees.
- The house is 2500 sq feet (not counting the basement of course).
-One and 1/2 storey 1857 log cabin.
-New roof and spray insulation
-Windows need to be replaced, so I currently lose a lot of heat there
-The duct work might need some additions, and more return air ducts added
I assume that I need two heat exchangers- one for the shop and one for the house?
What size would you recommend for each building?
I want to be WARM!! I live in the snowbelt in Ontario, Canada and we have brutal winters, so I want to make sure that whatever I use in the heating system is going to be large enough to make sure I stay warm * happy

Any help or information you can give me would really be appreciated!
Thanks.
Patti

It's always best to run a heatload for all the spaces. Room by room is best for the dwelling units. Plenty of easy to use load calculators available. I believe Slant Fin has a free heat load app now.

Realistically your boiler output would be 25,000 x 3.41 = 85360, time the efficiency, call it 80%. So you have an actual output closer to 68,000 BTU/hr. With the fire cranking

If you don't have a furnace already, consider sizing an air handler with a hydronic coil built in. You could also add a cooling A coil if AC were to be desired. Basic air handlers without burners are not too expensive and you get the blower, HX, controls, filter rack, cabinet with standard sized ducting flanges. Nicer ones have ECM variable speed blower motors.

"Google" hydronic air handlers and you will fine plenty of selection.

I have used these mounted horizontally to heat metal building shops, where radiant slabs were not an option. Real fast recovery with forced air

 

[Patti]

Thanks for the info Bob! I will discuss with my Plumber / HVAC friend who is installing my system.
Thanks again.
Patti

 

[maple1]

Seems on the face of it that you'll have a pretty high heat load for the size of the boiler. To me anyway.

Not sure how well it correlates, but my '40kw' wood boiler burns between 6 & 10-12 hours a day in the winter (10-12 being coldest of days) keeping just our house (20 year old 2700 sq.ft 2 storey) & DHW warm. I suspect it will need to be burning with the fire cranking almost all of the time. Good luck!

 

[Tennman]

Patti, We added a water-to-air heat exchanger (HX) to the existing propane furnace ductwork in our root cellar. It already had a coil in it for our downstairs AC, so the HX for the boiler went downstream of it. I measured the cross section of the duct plenum, about 24" x 24" by memory, then called a HX manufacturer recommended here on the forum (sorry, can't remember, been awhile). Bob, gave you the energy output, that combined with the air flow rate (CFM) of the blower you'll be using or have, the HX guy then determined the HX thickness to achieve the energy output that would fit in the existing ductwork. All this assumes using an existing air handler if you have one. Ours arrived in about a week. A search here may turn up recommended HX manufacturers. Been awhile since I've seen a HX discussion. Others may have recommendations on HX suppliers. Seems your boiler supplier should help you with this.

Congrats on the old cabin. 1857 is about the same vintage as our old place. Easy to imagine those settlers shaping those logs by hand. Best wishes

 

[Patti]

Seems on the face of it that you'll have a pretty high heat load for the size of the boiler. To me anyway.

Not sure how well it correlates, but my '40kw' wood boiler burns between 6 & 10-12 hours a day in the winter (10-12 being coldest of days) keeping just our house (20 year old 2700 sq.ft 2 storey) & DHW warm. I suspect it will need to be burning with the fire cranking almost all of the time. Good luck!

Yikes! I am starting to get a little concerned.... I had an 80,000 forced air propane furnace before, and I was assured that this 25kW Woodpecker system would heat my house and shop no problem....Thanks for your input!

 

[Patti]

Patti, We added a water-to-air heat exchanger (HX) to the existing propane furnace ductwork in our root cellar. It already had a coil in it for our downstairs AC, so the HX for the boiler went downstream of it. I measured the cross section of the duct plenum, about 24" x 24" by memory, then called a HX manufacturer recommended here on the forum (sorry, can't remember, been awhile). Bob, gave you the energy output, that combined with the air flow rate (CFM) of the blower you'll be using or have, the HX guy then determined the HX thickness to achieve the energy output that would fit in the existing ductwork. All this assumes using an existing air handler if you have one. Ours arrived in about a week. A search here may turn up recommended HX manufacturers. Been awhile since I've seen a HX discussion. Others may have recommendations on HX suppliers. Seems your boiler supplier should help you with this.

Congrats on the old cabin. 1857 is about the same vintage as our old place. Easy to imagine those settlers shaping those logs by hand. Best wishes

Thanks so much for your help! I will give this to my Plumber friend who is installing the system for me. (he used to do HVAC too!)
Your house looks gorgeous!! These oldies-but-goodies are definitely a Labour of Love aren't they I've had it for 12 years and every day I still look at those huge hand-hewn beams with awe and respect!!

 

[maple1]

Yikes! I am starting to get a little concerned.... I had an 80,000 forced air propane furnace before, and I was assured that this 25kW Woodpecker system would heat my house and shop no problem....Thanks for your input!

I might be off base a bit too, always a chance of that. Did the propane unit heat all the same things the pellet unit will be heating? Shop too? And were you always as warm as you wanted to be? That's one factor that's kind of hard to guage - I know now that I have a good wood burner, our house is always warmer than it used to be with the old one which kicked the oil in once in a while to keep up.

Maybe you'll get more feedback on this part from others - but a heatload calc suggested by Bob above should help tell.