Ok guys need a heating expert. I have 3. Base heaters and a 500 sqft garage, I have these water heaters as well that are not in use. So I was thinking of making a heating system for the garage. Could the heaters support the load?

 

what kind of delta T are you looking at?
whats your wall's R value?

 

Let me expand on the plan. I forgot to mention the purchase of 3 extra radiators. As far as the values I'm not sure to be honest its all block. No additional insulation is installed.

 

I'm getting ready to build a stick frame 32 X 40 garage.
I'm hoping to use solar as a primary heating system to keep it above freezing.

 

king,

Just as a general rule of thumb, 25 BTU/sq. ft. of living space will heat quite nicely with a reasonable amount of insulation. With lots of insulation or mild temps you could go to as low as 10 BTU/ sq ft.

Baseboards come in various outputs. But for the sake of argument figure about 500-700 BTU / linear foot at a water temp of 160* and an ambient air temp of about 65*.

So, for a 500 sq ft room you might want about 20 linear feet of baseboard. Less means a higher water temp, more means lower. Less for mild climates, more for more severe.

A small circulator will move plenty of water to make this work fine. Something in the 1/20 HP range like a Grundfos 15-42 stainless or a Taco 007 bronze.

Gas water heaters have their BTU inputs listed on the front. It's not about gallons, just BTU input. Take the BTU listed and multiply times .7 to get the output. Tankless water heaters can work, but often they are a problem so do some homework before committing to one of them for this purpose.

If you want to use solar you must use as many linear feet of baseboard as will fit in the room because the delivery temp will often be lower than desired and solar efficiency is based on temperature. The lower the temp the higher the efficiency.

 

Ok how does the water heater btu input into the problem? Like how much heat does each radiator absorb

 

you are only losing a fraction if you follow the basic calculation formula. 500 sq ft is tiny, so the pump and circulatory system will not be needed to run much.

state your location, average temps per season, as above- simple one inch foam foil faced for block walls, will keep the condensation factor (above ground or any walls below grade?) to a minimum and raise the temp loss with a R-14 insulation factor (dow product) if the garage isn't built yet, pour styrofoam pellets into the concrete cores for low humidity/condensation and a R-22 or better....

shoot- with one 30 gallon hot water tank, two opposing baseboardheaters at the door area and the confined area, I would include the forced air hanging radiator shop fan for an economical loop system with a temp drop of 20 degrees max on the return. insulate the copper three quarter pipe, pump needs open area for cooling for a 75 gallon to 90 gallon antifreeze system.

we built a hydronic heat system that runs off our outside wood boiler or can be switched over to propane when not around or season changes. we have a spur that heats the barn, but we don't need it. 6000 sq ft house with apartment has heat in the concrete floor. THE place to be for the winter! on 800 dollars a season.....

get info for your equipment, taco has excellent product life, and don't be in a rush. talk to everyone and keep notes. this is just a math problem, no worries.
sweat the pipes first for a solid solder.
let us know...
heidi

 

Look into SIPS (Structural Insulate Panels), they go up quick and your done when their up.. Very hi R value. I set a 32x50 shop in little over a day..

 

I don't understand what you are asking here.

The water heater input (in BTUs) is the energy that is used to do the heating. The energy going into the water heater heats the water which then gives up it's heat (BTUs) to the house, by getting cooled in the baseboard unit. The water heater output is about 70% of it's input and it's output goes to the radiators and to the house. The other 30% goes out the vent and is lost. Radiators don't absorb heat, they radiate it, or convect it to the surroundings. They are just the delivery system.

The number of gallons in the water heater is meaningless. It's the BTU rating that determines how much water, or how much space, it can heat per hour. But usually a 40 gallon water heater will have about 35,000 to 40,000 BTU input. A high recovery 50 might have 65,000 BTU.

Match the output BTUs to the load of the house with the calcs I suggested in my previous post. Go straight from BTU input, to efficiency (70%), to required load (25 BTU/sq.ft. max) to linear feet of baseboard to match this load.

Unfortunately, most water heaters won't crank up past about 130* or so. So you can add more baseboard or accept a smaller amount of heat delivered.

These can be plumbed very simply. 3/4" copper and a small circulator plumbed in a loop from hot and back to cold. If the water heater is also delivering hot water to the house just tee into each line. If it's dedicated just to heating you'll definitely need a few more parts, but it's still simple. The circulator can be controlled in a couple of ways with a wall thermostat and the whole thing becomes automatic.

Radiators, like the old steam radiators are different. They are made of iron and the newer ones from steel tubing. These cannot be fed with standard drinking water from a dual purpose water heater that also makes hot water for the house. Water heaters for this purpose must be dedicated to that purpose only.

There are many variations on this overall theme. More information might help.

 

Yeah when I was asking how much heat the radiators absorb I was trying to figure out what kind of output I would require from the water heaters. So let me see if I understand the math correctly. Let's assume the radiator has a btu value of 500/ft. So a 10 ft long radiator would produce 5000 btu if I understand correctly. So if my water heater output was say 40000. Does that mean each radiator would use 5000 from that number? Leaving me with 35000 btu for the secont radiator? As for conditions. I live in lower mn. So winter temps sit between 0 and 20 usually. Sometimes hit negitives. Also this would be a didacated system. I've found a place I can get free water heaters because if this works small scale I also have a 6600 sqft shop ill attempt something similar. Thanks guys for the help!

 

I have a tankless hotwater heater and am familiar with their operation.
My unit is 185,000 btu, has a digital panel that I can set the outlet water temp from 130 degrees F to 175F. And it requires a min. of .6 GPM to fire up and start heating the water. Yours may be different.

I would think that for a 500sf garage the radiators you have should work fine if the garage is insulated. If not you could just add units until it works for you. I'm thinking that you could raise your output temp. on your unit like mine so you could easily get the baseboard heaters hot enough. I would consult with a plumber on the best design for check valves/flow tie into house/expansion tank needed etc.

 

king,

Are you planning to use a tankless WH or a tank type?

A tankless will have to be one that can accept hot water on the cold input side if used for space heating and it will have to be one that can throttle down to match the output of the baseboard units.

So, if you had 4 baseboards that were 5000 BTU each and you had a tankless water heater with 84% efficiency, you would need it to throttle down to 20,000 BTU plus 14% (efficiency correction to match the input value) for a total of 22,800 BTU input. Make sure it will throttle that low or lower or else it will constantly be cycling and sending varying temps to the baseboards. This might make some noise and will not be as nice mechanically, or as efficient.

A dedicated tank type might be better unless the other can handle the hot on the intake and run at a low enough output. Once you are settled on the type of heater we can talk about plumbing schemes.

By the way, your example is correct. If the water heater is 40,000 BTU input and each unit delivered 5,000 BTU, you would really have 40,000 BTU input times 70% efficiency or 28,000 output. At 5000 BTU per unit you could run 5 units. Of course this is a variable amount based on water temp and room temp. So you could really run 6 units at a slightly lower delivery temp.

Go back to your 25 BTU/sq ft requirement and see if the water heater output (70% of input) matches that requirement. Then just add up enough linear feet of baseboard to deliver the heat. It's really quite straight forward and there is a lot of room for variance in design.

 

Ok so for this example. 25 sqft needs 12500 btu. So I need a water heater producing 12500 btus and enough radiators to distribute the heat? As for the type of heater. I first designed with the tank water heater. Then thought id stick the instant farther down the line( will pry be how I d the big shop. So in that application id have point A then say 5 radiators then a heater then 5 more and so on. By the way I'm justthrowing numbers. But sine the water heaters are freebies. I figured id try this before the outdoor doiler

 

Ok so for this example. 25 sqft needs 12500 btu. So I need a water heater producing 12500 btus and enough radiators to distribute the heat? As for the type of heater. I first designed with the tank water heater. Then thought id stick the instant farther down the line( will pry be how I d the big shop. So in that application id have point A then say 5 radiators then a heater then 5 more and so on. By the way I'm justthrowing numbers. But sine the water heaters are freebies. I figured id try this before the outdoor doiler

 

Sort of ..... what's the efficiency of the system you're using? That's going to really determine how many BTU's you'll need.

Using your example, if 25 square feet needs 12,500 BTU's and the efficiency is 70% you'd need 17860 BTU's. If your efficiency is 84%, then you're looking at 14880 BTU's.

For the math part of it, take the BTU's you need and divide by the efficiency rating, then multiply that number by 10. This gives you the BTU's that you really need to get the amount of heat you want.

(BTU/efficiency) * 10



Kris