Boiler size for in floor heat pole barn

[bmxer883]

Hi so Im finally ready to install a system in my pole barn but looking for some help.

My building is 40x48x14 2 in spray foam walls blow in the ceiling 1in foam under concrete. I do have lots of doors (2) 10x10 (1) 12x12 (1) 8x8

Seems insulated good it's been in as low as 40s in morning and 60-70 in after noon and building stays at 65. I have a patio heater think it's like 35000btu and that will bring the temp up pretty fast.

So I have 6 loops in my floor for in floor heat should be 300 ft runs. I live in pa so cold winters trying to find a good heat system. A professional said they would install a tankless boiler and everything ready to go for 7 k seems high.

I can do all the plumbing work and have looked up all the components I need just wondering on boiler I also looked into a tankless hot water heater to do it some say they can be used for hydroponics. My father in law uses a hot water tank for his garage and was very cheap to do his system.

 

[PoorUB]

1800 feet of tubing. Depending on the size of the tube you are 15 to 30 BTU per foot of tube, depending on who you talk to. 1800 x 30 equal 54,000 BTU. That is the most BTU you can shove into the floor so no need to be any larger than that. if you go with 15 BTU per foot you can cut that in half, so 27,000 BTU. I would recommend 50,000 BTU. You need to figure out gas or electric. You can go larger, it won't hurt if the unit modulates, but keep it reasonable. Keep in mind going larger will get get you more heat. You are limited by the amount of tubing in the floor.

 

[PWC Repair]

I agree, go with 50,000 btu. In PA you WILL need it through part of the winter.

 

[danski0224]

Somewhere between "too small" and "too big" lies "just right".

That's the one that you want.

 

[theoldwizard1]

My building is 40x48x14 2" in spray foam walls blow in the ceiling, 1" in foam under concrete.

More insulation ! Not sure where you are located but 12" in the ceiling woul be my minimum. 2" plus vapor barrier under the floor.

I have a patio heater think it's like 35000btu and that will bring the temp up pretty fast.

With all of those doors you are going to want and auxillary heat source to bring the temp up fast. Radiant floor is very comfortable but does not recover fast.

 

[PoorUB]

With all of those doors you are going to want and auxillary heat source to bring the temp up fast. Radiant floor is very comfortable but does not recover fast.

Oh, how wrong you are!! Sure the floor does not recover if the floor cools down, but you have this huge mass of concrete that has a ton of BTU soaked into it. Open the shop doors, let the wind blow through for a half hour, close the doors and in 15-20 minutes the space will be back to temperature.

We witnessed this at the shop I worked. There were many times we were moving freight in and out for a half hour or more, sometimes at below zero temps. Close the shop doors in a short time the space is back close to set point.

 

[stingry]

PoorUB
Exactly!! I have a radiant floor in my 3600 sq ft shop which I keep at 65 degrees air temp. I can open the overhead door and the air cools of but as soon as I close it I can stand in front of the door and feel warm!! I can't overemphasize how much I enjoy radiant heat.

 

[theoldwizard1]

I can't overemphasize how much I enjoy radiant heat.

I have always said it is the MOST COMFORTABLE form of heat !

 

[bmxer883]

I forgot to mention it will be natural gas I have a well out back.. I thought 50 was pretty small so glad I asked. Would it be bad if I go bigger like 75-80 if I can't find a 50?

Also do you think I need more insulation in my building it seems good but haven't gone through winter yet and the walls are still open so I could add more insulation

 

[PWC Repair]

Insulation.....https://www.energystar.gov/campaign/seal_insulate/identify_problems_you_want_fix/diy_checks_inspections/insulation_r_values

Heat source....Looks like the answer is above on post #2.

 

[bmxer883]

My walls don't have a high r value cause it's only foam but they are completely sealed so feel like that's better

 

[PoorUB]

I forgot to mention it will be natural gas I have a well out back.. I thought 50 was pretty small so glad I asked. Would it be bad if I go bigger like 75-80 if I can't find a 50?

Also do you think I need more insulation in my building it seems good but haven't gone through winter yet and the walls are still open so I could add more insulation

Depends on the boiler. With a modulating boiler you can go just about any size you want within reason! Single stage boiler I would not over size by very much, keep it less than 100,000 BTU.

I see guys using a 140,000 modulating boiler as they are less money. I am fine with that. Just realize you can only put roughtly 50,000 BTU in the floor so the extra boiler size is wasted.

 

[bmxer883]

Okay thanks for answering questions about size of boiler so now I have a second question to run water or glycol?

I have well water and I know it has a lot of calcium but think it's good other than that so didn't know if it would be okay or get distilled water. If I run glycol how would I have a fill valve added so it never ran low?