I need help with a backup plan?

FordMillwright1

I currently use a outdoor wood burner to heat 1200 sq ft of radiant floor heating. The wood master also heats the furnace and hot water tank through heat exchangers which saves on gas. The 1200 sq ft only heat source is the wood burner. No duck work in this area. I’m currently researching another option. I would like to have the option to go on vacation for a week and stop burning wood if needed. My house is a 5000 sq ft elementary school that closed down in the late 60’s. So venting a gas Micro boiler is a difficult option. Plus a over kill for a back up option that only needs to run maybe 2-3 weeks a year.

 I’m new to the radiant floor heating and wood burners. This is my 2nd winter in Michigan. I’ve been burning wood for five months and it’s a lot of work. Not sure if I can justify the time but the cost to heat this building without it would be scary. 

I see a lot of info on boilers. I’m not interested in a tankless water heater. But it’s a option. Is the Hydroshark electric boiler 19kw model a decent option? At 50 btu per sq ft. I need at least 60k. Please!!!!  Any input will be greatly appreciated. 

Jon_blaney

Are you looking for a whole house solution or just the radiant floor?

hot_rod

radiant in residential applications can get you mid to high 20 btu sq. ft. if your space in fact needs 50 btu sq you need supplemental heat 50 btu/ sq ft is huge number maybe recalculate that.
Next determine what your best fuel costs are, electricity is usually most expensive unless you have some low KW rates, like 5 cents per KW.

https://coalpail.com/fuel-comparison-calculator-home-heating

PerryHolzman

Electric boilers sized to keep the house at say 40F would be cheap, reliable, and costly to operate for the times you are gone... but, would have low maintenance cost.

The big issue is having a large enough electrical supply to the house to power them.

1st step is to do a heat loss on your house - for both normal room temperatures, and then assume 40 F room temperatures, and assume the coldest weather in the area.

Slantfin has a heat loss calculator that you can download and use.

Size your boiler at least 10% above to allow for errors.

Then you need to look at large an Electrical Service you need, with other active appliances and lights in the house - and is that plausible.

Note: it won't work if the power goes out... but then again, most other boilers won't work with the power out either.

I wish you well with this concept,

Perry

Edited to add: Is your wood boiler outside or in another shed; or inside the house. You need to keep it and any piping between it and the house from freezing as well...

PerryHolzman

Why the duplicate threads?

Jamie Hall

Welcome to the reality of heating with wood. The romance does have a way of wearing off...

The first thing you need to do is to get a good handle on what your real heating load is. 50 BTU per square foot sounds and looks suspiciously like a round number pulled out of the air -- or a doubtful guide. There are some very good calculators on the web -- Slant/Fin has one I like, but there are others.

Second, can you estimate how much the output of your wood boiler really is? Since you have some experience with it and how well it works, that would be a good guide too.

Third, how does this heat get into the space you are heating? You are not going to get 50 BTU per square foot of floor space; 25 BTU per square foot is much more reasonable -- and only from the active floor space.

Having pulled all that together, you can begin to think about what your auxiliary or backup heat source might be -- and what you are going to fuel it with. Hot water heat of some kind or another is probably your best bet, since it would seem from your description that you are using a radiant floor as well as some heat exchangers in a forced air system and for domestic hot water, and a hot water boiler will give you the most flexibility. The energy source for that boiler needs consideration, as the cost to run it -- even for relatively short periods -- may be significant in your thinking, and you have no idea now how much you really will run it in the future (as I noted above, one does get tired of wood heat after a decade or two...). I have no idea what electricity costs in Michigan, but you should very carefully compare the cost of a BTU rom electricity with a cost o a BTU from oil or gas (LP or natural). In some areas of the country, the cost of electricity is so high you don't want to do that if you can help it. I might note, too, that there is a hidden cost for electric heat: you may have to rewire your house and get a new entrance to power it, and you can't run it on a standby generator.

mattmia2

Depending on what the area is, electric or gas console heater or unit heaters are also options although I would be concerned about the floor freezing in some unexpected location without the water circulating. I guess it wouldn't be a terrible idea to have just enough antifreeze in it to keep it from bursting either way, in case you get sick or injured or have to go away in a hurry for some reason and can't fire the boiler.

FordMillwright1

I’m only looking to heat the 1200 sq ft of tile over concrete with the pex embedded.  The building has a lot of block interior walls. The roof has two different levels of flat torch down style. So some areas have high ceilings with no attic or ceiling void some areas have little space with no access.  Which running a gas line is a difficult option. Venting up to a flat roof with swimming pools and no pitch is another issue. 

I read an article about colder climates needing more btu per sq ft to heat. 50 btu is probably high and not accurate. But I’d rather have enough then not enough. Would 30-40 per sq ft be more accurate?

My gas bills with the wood burner running is less the $20.00 a month. The gas company thinks my meter is broke. 

I have no clue on how much electricity a electric boiler would use to heat 1200 sq ft. Concrete floors hold heat pretty good. Which should help cut down the run time daily. But I’m new to all of this. So please educate me. 

In the future I will be getting trusses on the roof. Then I will have more heating options. This building is a money pit. But it will be a fun project. It’s unique for sure. 

Thank you for all the input. 

EdTheHeaterMan

I'm guessing you can't ask the school board for an allocation in the budget for new heating equipment. That way the cost of your new heater can be evenly distributed over all the taxpayers in the district. LOL

For such a short usage, can you get a heat exchanger and pipe some hot water from your water heater and pump it to the radiant floor? What is the water heated with when the wood stove is off in the summer?

Erin Holohan Haskell

I've merged the duplicate posts into one here. Thanks.

FordMillwright1

My furnace and hot water tank are both gas with heat exchangers on them powered from the wood burner. When the wood burner is off.  The furnace keeps the water lines at 50 degrees. So as long as the pumps are running. The outdoor wood burner water lines won’t freeze.  

I have a 200 amp main panel. With a 100 amp sub panel in the middle of the building. I have plenty of power available and accessible. 

This is the setup that came with the building. I would like to tie into this with another pump  and a back up heat source. Not sure if I would have to close off the heat exchanger when using the alternative option. Would it effect the flow of the loop? No big deal to turn a few valves and reroute the antifreeze if necessary.

EdTheHeaterMan

So the easiest thing is to put in an electric heat source right next to the BPHX. I get it. Then is would use the electric boiler that most closely matches your BTU needs to maintain the room at 50° since you are not there when the back up is being used.

Jon_blaney

How about finding someone to come each day and wood up the boiler.

EdTheHeaterMan

Jon_blaney said:

How about finding someone to come each day and wood up the boiler.

At only $,000 per day

You know his house is over 5 miles away, up hill, in both directions, and my dad is not alive anymore.

Jamie Hall

Assessing heat loss by the square footage of a building is a fool's game. Fire up the Slant/Fin calculator and figure out how much heat you actually need.

And that is the heat you need -- concrete block or not. What the concrete block will do is make warming it up and cooling it off slower, so you will want to avoid setbacks, but it will not decrease the heat loss, nor the run time on the boiler.

Now if you actually do turn out to need 60,000 BTUh, you will need 70 amperes/240 volts for electric heat. You have adequate power -- you do not have plenty of power, but you do have enough.

mattmia2

As far as valving, there are multiple ways to do it. Primary/secondary pumping is one. A 3 way electric valve is another. The simplest is to just have the electric heat source in series and only turn it on when needed or have it on an aquastat that will only turn on if the wood boiler isn't providing adequate heat.