Bringing Heat to the Garage

[avc8130]

I'm in the planning stages of hopefully bringing heat to my garage. When I plumbed in my boiler I left a T in both the supply and the return for exactly this purpose. I went 1 1/2" on the Tee just so I could do anything I wanted.

Here's what I have:
House:
Wood boiler
T's in place in supply and return

Garage:
30 x 50 Pole barn
WELL insulated
Goodman propane furnace (hasn't had a propane tank in 3+ years).
My "idea" is to keep the shop ~50F to keep the chill out and then crank the heat up when I need to work in there. In the winter that is ~once/week.

The run: ~150' each way The garage is a bit higher in elevation than the house (<10') but the furnace is 9' in the air.

The "plan":
Water to Air heat exchanger in front of the current propane furnace.

My current thoughts:
1. Keep all controls in the garage to eliminate the need to run electric to the house. There is already a thermostat for the furnace, I can use that to trip a relay and run the circulator whenever there is a call for heat.
2. Use a Bumble Bee pump to allow return temp set point to get max efficiency.

Questions:
1. What should I do for the lines? Buy a pre-made setup? Spray foam? What size?
2. I know www.pexsupply.com is a great place for the pump and fittings, but they don't sell exchangers. Where should I get that?
3. How do I size the exchanger? By the rating on the propane furnace? By the physical dimensions of what will "fit"?

Any tips/tricks are greatly appreciated.

ac

 

[stee6043]

Ohh you're gonna pay through the nose for 300' of insulated pex. $3-5k ballpark?

Your garage will present a significant heat load I'm assuming. How big is your boiler? How often do you plan to load it? Is it worth keeping the garage always heated if you're only out there once a week?

With a garage that size I think your money would be better spent walling off a corner and installing a used boiler to service just the garage. Proper insulated pex is not cheap and the cheap stuff is junk (from what I've read). If you skimp on your pex run you're going to put a lot of wood in your boiler to heat the ground around your pex and not the house, not the garage.

 

[Armaton]

Should be able to find 1" Thermapex for about $11 a foot (10' increments), or 1 1/4" for $13 (50' increments) at least thats what it is here. That way you have supply and return in one handy package. 150-170 foot is probably all you need, depending on how far into building envelope you go with the thermapex, then transition to normal pex. Stee makes a good point about your load on the boiler, keeping that big of a building heated, (even just to 50 degrees) is quite a load. I got my WAHX from Outdoor Furnace Supply (OFS), if you ask, they have a performance sheet for each exchanger, that gives you the btu output at certain water temp input and fan cfm. I didn't know about the performance sheet untill it came with my exchanger, but I'm sure you could ask them to email you the specs for the exchanger size(s) you are considering using. Good luck!

 

[hartkem]

avc,

I plan on doing the same thing. My boiler is in a boiler shack with my 500 gallon of storage in the house basement. I buried 125' of thermopex to my 30x50 stick built shop but I am currently in the process of insulating so haven't hooked it up yet. When I asked this question last winter everyone though it was a better idea to spot heat the shop with my current boiler (eko40). Most people didn't think it would cost much to keep from freezing. I plan to keep the shop at 40F when Im not in there with an electric forced air furnace. Hopefully this works out for the both of us.

 

[avc8130]

I plan to JUST touch the building with the insulated pex line. The current forced air furnace is right on the wall closest to the house. I plan to keep the run as direct as possible.

When I did the heat loss calculations before I bought my boiler the garage took SIGNIFICANTLY less BTU/hr than my house. The garage is WELL insulated and extremely efficient (provided you don't keep the doors open ).

I'm not feeding 2 fires, that is just silly. Then I have the efficiency losses from EACH boiler.

Is Thermapex good stuff?

The main advantage to laying my own Pex and spray foaming is that I could add another line for water that would be "warmed" enough by the supply/return to prevent freezing. Right now I have seasonal water in the garage. It sure would be nice to be able to wash hands and cars in the winter.

ac

 

[hartkem]

I think thermopex is very high quality but expensive. In my case I wouldn't use anything else because of ground water issues. The thermopex is buried 3' along with my water line so I don't have to worry about them freezing.

 

[stee6043]

So what was the heat loss you calculated for the garage? What is your house heat loss? And what is the boiler you're running?

 

[avc8130]

So what was the heat loss you calculated for the garage? What is your house heat loss? And what is the boiler you're running?

I really wish I could find the calculation.

I want to say the garage was <40k btu/hr.

I'm running a WoodGun 180. I bought the 180 even though the house only needed a 140 specifically to heat the garage also.

ac

 

[ewdudley]

I really wish I could find the calculation.

I want to say the garage was <40k btu/hr.

I'm running a WoodGun 180. I bought the 180 even though the house only needed a 140 specifically to heat the garage also.

ac

Jim measures less than 15,000 btu per hour into a radiant slab for a well insulated 1500 sq. ft. shop heated to over 60 degF in Mn.

 

[avc8130]

Jim measures less than 15,000 btu per hour into a radiant slab for a well insulated 1500 sq. ft. shop heated to over 60 degF in Mn.

That is <40k isn't it . LOL

I think that might have been more like it. Maybe the house was 40k. Honestly, I don't remember. I just know that I have plenty of boiler.

ac

 

[BoilerMan]

The thermopex is buried 3' along with my water line so I don't have to worry about them freezing.

LOL, wow 3' I wish I lived in KC........

6' frost line here, and closer to 7' if you are under a driveway. LAY SOME BLUEBOARD!

TS

 

[avc8130]

OK, I did some more research/thought.

My current furnace in the garage I want to heat is 65k btu propane furnace. The air discharge is 19.5" x 19.875".

I assume that was sized properly, or at least close enough.

I have been talking with Andy at Outdoor Furnace Supply (site sponsor).

He suggests I go with an 18x17 exchanger that is rated at 110k btu at 180F supply temp.

He has been working through a few piping/pumping options:


65k btu at 20 delta T = 6.5 gpm

Assuming my run is ~400' equivalent I calculated the following head losses:

Pex:
1" Pex: 22.5' $360
1.25" Pex: 8' $675
1" Pex-Al-Pex: 12' $460

Pumps:
UPS26-99 $244
UPS15-58 $78
UPS15-58 $78

Here is where I get "lost".

I don't want to send water back to my boiler <140F. I can use an aquastat to only allow the pump to run if the supply temp is >165F (this is what I use on my "house" zones).

How does a 110k heat exchanger work when I only want/need 65k?

ac

 

[Nofossil]

If it turns out to be a problem, I suppose you could vary the fan speed on the garage HX to maintain a minimum return temp - or make a baffle to reduce the effective surface area so that you get an acceptable temperature drop.

 

[avc8130]

If it turns out to be a problem, I suppose you could vary the fan speed on the garage HX to maintain a minimum return temp - or make a baffle to reduce the effective surface area so that you get an acceptable temperature drop.

I had thought about that. My furnace is a Goodman GMV950704CXBB. It appears the fan speed can be varied from ~750 to ~1700 cfm.

I guess these water/air exchangers are actually designed around 12 gpm?

ac