Design a new system for existing shop.

rcrboy

I bought a home with a 36' D x 40'W x 14' H shop. The five loops of tubing was already installed and coiled up on the wall. The shop has R19 walls and R30 ceiling. I am looking for some guidance on putting together a boiler and all the necessary components. My first question is can I use a Navein boiler? And also what is the simplest system I can use? Thanks

GroundUp

The simplest is to buy a prefabricated system that's been designed and assembled by a professional. You absolutely can use a Navien boiler if you'd like, though they're not well liked by anybody who's ever had to service one. This isn't really the kind of thing that should be attempted without at least some sort of professional intervention, which will likely cost you a few bucks upfront but will save a whole lot more in the long run.

hot_rod

is there a good layer of insulation under the slab? Any idea on loop lengths.

1440 sq ft at a guesstimate 20 btu/ foot would be, 28,800 btu/ hr.

Cheap and easy but not high efficiency would be a gas or lp tank water heater. Tank, mix valve, pump air sep and expansion, it would be a simple build.

rcrboy

Yes there is 2" foamboard under the slab. The loop runs I was told are 275 feet each.

hot_rod

If it is something you or a plumber wants to attempt, here is a simple hot water tank concept drawing.

If this needs a permit, check with the inspectors, hot water tanks are not a listed ASME boiler. Although some brands and models are labeled for hydronic use.

The thermostatic mix valve allows the tank to run hot enough to not constantly condense. Adjust it as low as you can and still heat the space. It may take some trial and error.

Check with your inspectors if that applies.

Add the 30 psi relief valve. Leave the factory installed T&P valve in place in the tank.

A small 50,000 boiler is also an option if you want more technology.

A heat load calc would be another good idea to assure you get the heater sized appropriately. Find some free calculators online.

If you are windows based, www.hydronicpros.com has a free trial version of a simple load calculator.

rcrboy

52,318 heat load, 1 gpm flow rate per loop, 3.77 head loss.

rcrboy

correction, 52318 heat loss

hot_rod

Where are you located? The load number seems awful high for 1440 sq. ft

52,318 divided by 1440 = 36 btu/ sq ft?

If you have 275' loops of 1/2 pex tube here is the flow data at 1 gpm flow of 100° water

Screenshot 2025-01-17 at 3.08.48 PM.png

GroundUp

A: you'll never get 1 GPM through a 275ft loop

B: that heat loss seems really high, though Bob's seems relatively low unless you're not in a cold location

How are you coming up with this heat loss factor?

rcrboy

Sorry my mistake. I entered the wrong parameters. After carefully calculating again. The heat loss is 35k btu.

hot_rod

so 24 btu/ sq ft, I was a bit low with 20

.65-.75 gpm per loop is realistic

Here is what 1 gpm would look like in a 1/2” , 275’’ loop. Its possible with the right pump, but you should not need to go yo 1 gpm

IMG_9461.jpeg

.65 gpm per loop with 1/2@ tube 12” on center give you about 26 btu/ ft

rcrboy

What components would I need to achieve that? I am not familair with what are good quality parts. Such as manifolds, copper, brass, pvc, etc. Can I use a 80 gallon 80k btu water heater?

hot_rod

Yes that heater would work

a copper manifold would be my choice

Grundfos, Taco, Wilo, B& G circulator

Caleffi Discal air purger

Caleffi 520 mix valve

Caleffi 573 fill combo

Amtrol Pro expansion tank

Misc valves, temperature and pressure gauges

Or as @GroundUp mentioned, buy a pre assembled module and connect to the tank, and pex run a thermostat wire, , plug it into a wall receptacle

rcrboy

Thanks

Kaos

The bigger tank doesn't buy you anything here, even the smallest standard tank has a big enough burner to support your load. The bigger burner will also cycle more so your stack losses will be higher.

I would look at the Energy star website lest you look up the recovery efficiency of the tank, for space heat this is what matters. Since you are heating with expensive fuel, you want to get something with decent efficiency.

In terms of plumbing (assuming space heat only), with a tank the air separator is optional as the tank itself will collect the air. Most can also be turned down enough to run floor heat directly, even if that is not cold enough, a simple adjustable bypass is good enough.

I know some people are not fans of it, but I've had good luck with tankless units for space heat. Just make sure they are combi rated and you select a high head pump as they are much more restrictive than a tank.

hot_rod

I would definitely not run the gas or LP fired HW tank below dewpoint, around 130F.

I made this mistake on a number of "entry level" price-point radiant slabs., running the tank around 100°F Several years down the road the sheetmetal burners were badly corroded from constant condensation dripping down on them. Burning yellow from the badly rusted burner. A potential CO issue also as the flue soots up.

Even with a sloppy, inefficient HX tube in the tank, they still need to warm up occasionally to dry out.

A bypass valve is a guess at best, it works at the exact condition you set it only.

A thermostatic mix valve has intelligence, it knows when to make flow adjustments, it will keep the supply in a safe temperature range as the tanks heats beyond that required supply temperature. They are not expensive considering the consequences.

This is not a place to look to save a few bucks, from my experience.

Inexpensive hydronic components on E-bay if you are a shopper.

If a high efficiency system is a priority, a water heater in not the best heat device to use.

If you have an 80 gallon it will be a nice sized buffer, although some additional standby loss compared to a smaller tank.

Smaller 40 or 50 gallon tanks have around a 37,000 btu/hr burner, some smaller.

At 78% efficiency, I'm being generous, you have only 28,000 actual output. So a bit shy of your 35K load.

PDTech

I have a similar building. (Shop is 30 x 40 x 12' sidewalls) My insulation is about the same as yours. My calculated heat loss was a little under 20K btuh. Calculations must be close, because I use a 5500 watt electric water heater, and can keep temp 50 degrees above outside. Location is eastern Nebraska.

rcrboy

Your setup is exactly what I had in mind.

PDTech

I built this myself patterned after a fully assembled unit sold by Menards.

rcrboy

What size pump are you running in that setup?

PDTech

Its a 1/25 hp. Grundfos 59896341. I have 5 loops of 1/2 pex all between 200 & 250' each.

https://www.menards.com/main/plumbing/hydronic-radiant-heat/radiant-heat-manifolds-components/grundfos-1-25-hp-circulator-pump/ups15-58fc/p-1444433736251-c-8523.htm?exp=false