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In-Floor Heat Loop Design & Boiler Sizing

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heierlu

Member
Joined
Nov 27, 2014
Messages
19
Location
WI
I'm in the process of building my dream shop, and am finally at the point where I need to figure out in-floor heat, and what to do for a boiler.

The shop itself is 64'x56'16'. Ladder frame, wood construction built on a concrete foundation (4' frost walls with 6" exposed above ground). Will have R19 in the walls and at least R38 in the ceiling. I've got 3 12'x12' overhead doors and 1 20'x14' overhead door. The floor has yet to be poured. Will be doing 2" foam under the slab, and 5" thick floor.

I've looked around for quite some time and haven't been able to find a decent place to produce a loop plan. Sounds like 1/2" pex is preferred, with 300' maximum runs. Plenty of people said they just wing it when laying down the loops, but I'd really like to have a plan to go off of. The utility room is in one of the corners of the building, so a loop design seems more important in this scenario.

I've also done some research on boiler sizing, but every source seems to have its own method and numbers. I've come up with anywhere from 80-180 BTU boiler, so really not sure the proper calculation. I'm in WI and it can get down to -20 in the winter, so I want to have it sized appropriately. Also undecided on a combi-boiler. Is it better to go combi, or have a boiler for in-floor heat and then a small tankless unit for the bathroom and shop sinks?
 
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bg71361

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Joined
Jun 26, 2007
Messages
13
I have a 30 x 70 x 12, 4 loops, total 1600 feet in the floor, my unit was spec'd out by I think Radiant Floor. It's a Takagi TK Jr. 140k, I keep my floor at 51° and run the adjustable burner at around 100k. Your space is larger than mine 180k unit sounds like it's in the correct range.
Good luck!
 
J

jblnut

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Jan 17, 2015
Messages
6,976
Location
In the Middle of MN
Central MN here so same as you for cold crappy winters.

I have a 54x72x18 with a 120k BTU IBC boiler and it does it without issue. One small zone for the office and mech room and one big zone for the rest of the shop. All 300' runs. I have a slab stat for each zone as well. The boiler modulates from 20k-120k BTUs and I have rarely seen it over 80k.

I run the shop floor at 62F and it keeps the shop at 55-58 depending on the outside temp. I also have the air temp set to 54F but it almost never gets that cold in there unless the 26x16' door is open for longer than a few minutes.

They that say the piping plans aren't really needed are correct. When mine was done I had the outer 4 runs set at 8" apart, the next 4 runs at 12" apart and the rest at 16" apart. Make sure to have lateral runs along the outside walls. Under the garage doors I put the piping so it would come to the edge in a loop and not parallel with the walls. The thought is there would be a ton of heat lost in the pipe by the doors and I didn't want one run to come back waaaaaay cooler than the rest because it happened to be the one under the doors. Not sure if that would matter or not but it seems to work. The doors almost never have snow against them outside and that is soooooo nice !!

I put foam 2' down around the outside under the slab and 2" thick under the floor. I wanted to do 3" thick around the outside 8' and then 2" for the rest but I didn't. Don't remember why it didn't happen other than I had a lot of **** going on and forgot to get some 3" stuff. We put 4" of foam under the house. I got it for almost nothing so we thought why not !! Most will say that is overkill and a waste of money but guess what, it's my money lol

I really wish I'd have put a pex line from the mech room to my floor drains as I could have dumped the condensate down the floor drains instead of into my holding tank. It'll generate 7gal a day when it's windy and -25f outside. I run a fair bit of water down the drains and they don't freeze so that wouldn't have been and issue here I guess.

I did a standalone boiler and a 6gal electric water heater. I don't regret it one bit. I didn't think it made sense to have the boiler running all summer just in case I wanted to wash my hands or do dishes once a week. That route was also less expensive than doing a combi as well.

I'd be happy to post some pics of my setup if you'd like.
 
P

PoorUB

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Mar 29, 2021
Messages
11,622
Location
Fargo, ND
I have laid thousands of feet of tube and rarely used a layout drawing. Space the loops a foot apart. You may want to run the first two or three loops along the wall tighter, but I have done it either way.

You will only get about 25-35 BTU per foot of tube, depending one who you talk to. If you lay out the loops a foot a part you will get very close to one foot of tube per square foot of floor. 64x56=3584 sqft. 3584 sqft x 30 BTU per foot gets you 107,520 BTU.

80% boiler, roughly 135,000 BTU, 95% boiler, roughly 113,000 BTU. No reason to put in anything larger unless you put in more tubing, tighter spacing, but trust me, you will not need it.

Just to clarify, I laid floors in North Dakota so I am experienced with cold weather.

Some guys will do more math, just add more confusion, but I will bet the numbers will come out very close to the same.
 
J

jblnut

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Jan 17, 2015
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In the Middle of MN
heierlu said:
@jblnut - I'd love to see some photos of your setup!
Click to expand...

Setup in the house .... The plate exchanger in there is for the outdoor wood boiler loop for the infloor system ....
KIMG1644.JPG

Shop stuff. Expansion tank is above the pic..... Plate exchanger is for the wood boiler loop again .... The IBC boilers have internal circ pump so an external pump for the primary/secondary loop setup isn't needed. Looking back I really wish I'd have gone with a non pressurized LP boiler so I could have done a primary/secondary loop setup for the wood boiler instead of the dumb plate exchangers.
KIMG0781.JPG


If you'd like more pics of something let me know.
 
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F

fitter30

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Jun 23, 2019
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Location
Peace Valley,mo
Property design radiate floor heat the design water temp 10° over thermostat setpoint. Any high efficiency boiler 95%+ the return water temp has to be 140° or lower. The lower the efficiency goes up above 140° efficiency drops to 87%. 16" on center loops are to large 12" is standard. When cement is poured any tubing in pour must be pressurized to 25-30/lbs air.
 
F

fitter30

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Jun 23, 2019
Messages
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Location
Peace Valley,mo
Two Pump Chump said:
Stop calling a heater a bolier.
Click to expand...
Water heater Heats potable water comes in cold and hot out
Boiler Heats water or makes steam for closed system heating and isn't potable. Residential boilers can have a optional coil build in for heating potable water sometimes call a sidearm.
 
T

Two Pump Chump

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Sep 27, 2020
Messages
106
Location
N CA
Does it boil water or heat it ? Does it provide heated liquid or bolied liquid ? Misnamed is misnamed. And many tankless heaters are called exactly that by their manufacturers. "water heaters" also heat glycol mixes in radiant applications. It's just sloppy laziness that is self perpetuated. Do you want boiling water ? It's dumb.
 
F

Firebrick43

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Joined
May 12, 2015
Messages
13,998
Location
West central Indiana
Two Pump Chump said:
Does it boil water or heat it ? Does it provide heated liquid or bolied liquid ? Misnamed is misnamed. And many tankless heaters are called exactly that by their manufacturers. "water heaters" also heat glycol mixes in radiant applications. It's just sloppy laziness that is self perpetuated. Do you want boiling water ? It's dumb.
Click to expand...

We also drive on a parkway and park on a driveway.

English is sometimes not perfectly logical.

A boiler is and heater of liquids that said liquids is used for space heating and has been used in this context for a long time irregardless of actually raising the liquid above it boiling point.

Get over it scooter, that is they way things are. Worry about something more important and less pedantic
 
P

PoorUB

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Mar 29, 2021
Messages
11,622
Location
Fargo, ND
Two Pump Chump said:
Does it boil water or heat it ? Does it provide heated liquid or bolied liquid ? Misnamed is misnamed. And many tankless heaters are called exactly that by their manufacturers. "water heaters" also heat glycol mixes in radiant applications. It's just sloppy laziness that is self perpetuated. Do you want boiling water ? It's dumb.
Click to expand...
Give it a rest!

Are you prepared to change the whole industry?

Here is a web site of a well known brand, and every thing they sell is a "boiler" with only a couple steam boilers on the page.

US Boiler

Another one, Do I need more examples?

NTI Boilers

This is as silly as the BTU vs. ton argument for air conditioning. Both terms are widely used.
 
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