Semi- temporary heating solution using wood stove and hydronic heat

Homesteady

Greetings from our drafty New England farmhouse!  In 2022 my wife and I decided to leave the big city and move out to our 200 year old abandoned farmhouse so we could actually start living out our dream of fixing up this poor old house, instead of always just talking about it.  We are doing all of the work ourselves.  For the past two winters we used two wood stoves for heating but, as expected, the distribution of heat was poor.  Now we are at a point where we are looking to start building our heating system.  

This house never had a heating system (back in the day they had a wood stove in every room) so we are working with a blank canvas and we get to create whatever system we want.  I’ve been doing a lot of reading/learning about hydronic heating systems for about 3 months now.  I begin each day doing my morning research and building systems on paper.  I am seeking feedback on some designs I made from anyone who wishes to chime in.  I am all ears.

Some key points:  

• This is a TEMPORARY heating solution to get us by for one, maybe two, winters.  We do not have a boiler and won’t have one for another year or two but the plan is to get one eventually, sooner than later.  
• We would like to build something that we can connect to a boiler when that time comes. We don’t want to put time and money into building something that we have to rip out later (unless the amount of time and money required make that worthwhile). We are willing to invest time and money to achieve this.
• The idea is to heat water from a storage tank using our wood stove (water jacket) and then distribute heat to the rooms using slant fin baseboard.  The wood stove is a Vogelzang 152K BTU unit that we purchased new last year, house is around 2500 sq.ft. I have no idea how much water I should use for heat storage, I only picked 400 gallons because that’s the largest tank I can find at a reasonable price.
• Second floor heat would be nice but is totally optional for this.  We have two bedrooms located above the wood stove with floor grates and electric baseboard heat.  We will eventually want heat upstairs when we get a boiler but for now it’s not necessary. 
• My full time job is renovating this house so I am always here keeping an eye on things, fixing things, keeping the wood stove filled, etc. so a “set it and forget it” solution is def not the expectation.  
• Basement is stone foundation and dirt floor, and has high humidity.  We are planning to pour a concrete basement floor next year. 
• Water comes from a shallow well and runs through multiple filters and a water softener.  

Attached are images of 3 layouts.  The first two were designed to be gravity systems which use an old water heater as a closed tank, but I’m not sure if I configured this right. The only difference is the number of circulators used and the use of a 3 way valve to push hot water directly into the HW tank first to get heat going faster when everything is cold.  I understand gravity systems normally have a tank/vent open to the atmosphere at the highest point but in this configuration the water never gets hotter once it’s transferred to the WH tank, so is that really needed if there’s no thermal expansion? #3 is zoned and is the one I’m leaning towards, as it seems to be the best option to merge with a boiler later on, but I’m worried about corrosion since it’s an open system.  How worried should I be about corrosion if I’m only planning to use this for 1-2 winters?  I purchased all new components so I don’t want them to get beat up- I’d rather buy some cheap Amazon parts and save the new Taco components for later if corrosion could be a problem.
So do you think this is a decent starting point? I’m curious what you would do if you could start fresh with a blank slate.

Thank you for your time and any feedback!  This site is a treasure trove of information and I truly appreciate all the time, effort, and information people pour into these discussions!

 

DCContrarian

Pex plumbing is easy to do semi-temporary, just run it outside of the walls. Slant-fin is about $12 a foot so you're looking at about $1200 for that, maybe a few hundred for PEX and fittings. Slant-fin is going to require a circulator, another few hundred for that.

Did the stove come with a manual? I'd start there.

Honestly, I would focus just as much on insulation. While nothing is harder to predict than the future, there's a good chance that by the time your renovation is finished combustion appliances will be on the way out. So your long-term goal should be getting the building envelope tight enough that a heat pump can meet your heating loads.

This article shows how to treat a old stone foundation and bring it to modern standards:

https://buildingscience.com/documents/insights/bsi-041-rubble-foundations

hot_rod

Does the wood stove have a hydronic heat exchanger already? If not that will need to be a custom or homemade component. I prefer the type that fasten to the outside of the stove to stay out of the fire.

You will want a thermometer on the flue to assure you don't pull that temperature down with the hydronic HX, causing creosote formation.

A plate heat changer is an inexpensive way to keep the distribution a closed loop piping circuit. Go with a forced circulation system, gravity would involve large piping and careful design and installation.

I'd also consider cast iron or panel radiators for a nicer look in a home like that.

Invest in a good quality CO detector also.

Jamie Hall

A fundamental problem. Old gravity systems — which worked splendidly well, but used big pipes — always had a tank open to the atmosphere at an elevation higher than the highest radiation. Often in the attic. Why? Because you want there to be positive pressure in all the piping and radiation. Modern system use either a compression tank or a bladder type expansion tank, and are closed.

Your first two systems seem to run as closed systems (and you do need the expansion tank, even for minor temperature swings), but I do not see how heat is transferred from your storage tank to the 40 gallon tank. There seems to be a supply line — but no return line in the first two systems. Nor do I see a pump to get water from the open storage tank to the presumably pressurized 40 gallon tank.

The third system would work, provided the pump were powerful enough to purge all the radiation every time it started. unlikely. Otherwise, at least some of the radiation will likely be airlocked and won't heat at all. Granted, sometimes this type of system can work reliably, if there are absolutely no leaks in the plumbing so that once it is purged it will stay purged. I wouldn't want to count on it.

I'd look closely at @hot_rod 's comments, and consider a plate heat exchanger using the large storage tank essentially as a great big buffer. One pump for circulation to an from the big tank and the wood stove, and one pump for the now closed heating system.

Now for a completely different topic. That basement.

Live with what you have and observe it long enough to observe if, and how, ground water moves into the basement. It is not at all uncommon for houses (or barns!) with stone foundations to be actually below the water table, at least in the spring, and for water to come — quite harmlessly — through the wall and seep into the dirt floor or, if you are on a hillside, out the downhill side. I have seen many attempts to prevent this

The approach outlined in the article you linked will work. There is one absolutely critical point about it which they are a little short on: provision is still made in their scheme for water to come through the stone foundation behind the new "bathtub" and exit somewhere. Do NOT simply apply foam or concrete or anything else directly to the stone foundation. It WILL crack and let water in anyway, guaranteed — but you just might succeed in keeping the water from draining back out, which is not good news.

I've also seen cases where water backed up enough outside the now almost sealed wall to put enough force on it to cave in the wall. This can ruin your whole day…

Depending on your house and its siting, and how you plan to use the basement (if at all), it may be much more satisfactory to place a vapour barrier and insulation under the ground floor. And much cheaper… And live with a damp and cool basement.

hot_rod

This issue shows a few ways to deal with open buffer/ storage tanks. Internal HX coils or external plate HX. Coils can be made from pex also. Tom from American Solartechnics up in Maine, may still be able to put together a knock down trank system.

Formulas for sizing the buffer in here also. But you need to do some number crunching for exact answers, like a heat load now and in the future.

https://idronics.caleffi.com/magazine/10-hydronics-wood-fired-heat-sources

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Grallert

I'll leave the basement alone here. Build the system as you imagine but I would use high mass emitters., tested cast iron radiators from a salvage yard, I've had good luck. Make sure they're for water. This or panel radiators. I would do as Hot Rod and Jamie mentioned and use a heat exchanger for the system this will keep the everything in the system cleaner and easier top control . Once your system is set up you can decide and figure out how you're going to heat the water safely. It can be really hard to control water temperature with a wood stove. It's not hard to flash the water to steam. This can also make pex something to think about. Now if you can gain good control over the temp of the water pex is a great way to move that energy around and high mass emitters will lend themselves perfectly to your future efficient boiler or heat pump.

hot_rod

If the stove HX is lower than the tank, that is a good thermosiphoin over heat protection. DC circulators or a small UPC could keep a circ running through a power outage also

. The concerns with wood boilers or stoves is over-heat protection and no power conditions. You want those systems to be fairly automatic in the event you are not home when power goes down.

It comes down to how much $$ and time you want to throw at a temporary system.

Bob Harper

How is this stove to be vented? Masonry chimney vs. Class A ss? What about clearances to combustibles, type of connector (stovepipe)?

Note that while listed to UL1482 and certified to EPA 2020 emissions, those remain valid only as long as you don't modify the stove. A hot water coil is not a listed accessory for this stove. Their addition can result in chimney fires as well as the spillage of smoke and CO into the home due to reduced draft pressure caused by excessive heat transfer. Modifying a stove is a violation of EPA regs. and the building codes. Should something bad happen, not only could an insurance carrier deny a claim but if anyone was injured, you could be held criminally liable.

Every year we get DIY'ers thinking about heating potable hot water with a woodstove and I ask the same question: If it was such a brilliant idea, don't you think every stove mfr. would have a water heating option?

Regardless, you're out of time with this late start. You'd be better served heating with the woodstove then take the money you would have spent on the above ploys and invest it into a small listed gas water heater and make do with less until you can afford better.

EdTheHeaterMan

Farm house with lower cost baseboard radiators. Not my first choice for that type home. If this had a heating system that was installed 100, years ago, the period radiator would look something like this.

And purchasing those NEW from a supplier will be expensive. However there are some scrap iron businesses that sell those older radiators at a much loser price point. Of course if that is not what you are going for then the baseboard radiator is an acceptable choice as ling as you use enough of it to heat the home. Your first step is to have a Heat Loss of the rooms to be heated to see what size radiator you really need. Once you know the amount of heat each room needs, then you can start to lay out those radiators and how to connect them.

From what you have shown so far, It appears that you have an uninsulated building from the early 18th century. The second thing is that I would not run an open system with the water I am using for bathing and cooking, in the same water that I am using for heating the building. Those pipes will get no circulation for several months in the summer. That is a recipe for bacteria growth. When you start the heating sirculator in the fall, You will be moving all that junk into your potable water supply.

HotRod has some good diagrams the use heat exchangers to keep the potable water separate from the space heating water.

Homesteady

Good evening and a HUGE Thank You to all of you who chimed in.  Your thoughts and feedback are very much appreciated.  The links and screenshots are incredibly helpful.  I updated my design which includes a plate exchanger to keep the open and closed tanks separate and I removed the direct connection to the domestic water supply.  A gravity type system is off the table.  We are making progress but I am wondering if I there is a way to reduce the number of circulators?  Would it make more sense to connect the wood stove hot water return directly to the plate heat exchanger and connect the old hot water tank hot supply to the heat exchanger before it goes to the radiators?  That would reduce the number of circulators to 2. 

 To address some of your thoughts and questions:

 The wood stove is connected to a stainless steel liner inside a brick chimney.  There is double wall pipe going from the stove to the chimney liner. It does not have a water jacket (yet).  The idea is to use copper pipe on the outside of the stove.  The left and right sides of the stove each have a removable heat shield with a 1” gap between so I will run 1/2 ” copper pipe inside there.  I will monitor the flue and stove’s performance and creosote build up closely for any changes or impacts this may have.  My guess is that wood stove manufacturers don’t provide water jackets as a standard feature, not because it isn’t brilliant necessarily, but because the demand just isn’t there to justify the added cost.

 The house is a ~1830 Greek Revival.  It’s a timber frame structure with two layers of 1 5/8” vertical planks.  There are no studs, so no space inside the walls for insulation or pipes.  We have been renovating the interior, room by room.  Since it is important to us not to disturb the wood trim (which is elegant and beautiful and original to the house), we chose not to build out the wall for insulation.  We removed the plaster and lathes (which were beyond repair) and installed 7/16” cdx plywood directly over the planks and then 1/2” drywall (5/8” on exterior walls) which lines up with the trim nicely.  We restored the original wood windows and installed spring bronze weatherstripping.  I am making storm windows now.   We did insulate the upstairs ceilings.  This work seems to have resolved the drafts in those areas but this winter will be the real test. This work continues.

As for the basement, we installed a French drain around the perimeter of the stone foundation.  Since the house sits on the top of a hill, and since installing the perimeter drainage, there is very little water intrusion but it does happen from time to time, usually seeping up through the dirt floor when the water table is high.  It’s still quite damp/humid down there so we will place a thick sheet of poly over the dirt floor for the time being.  When we pour the concrete floor next year, we’ll place a layer of stone and then poly and then reinforced concrete on top.  A sump pit and a floor drain to the outside will be part of this work.  

While a heat loss calculation would be ideal, I don’t think the results would be of much use right now because so much is changing with this house.  We will have a new roof installed before winter and we are about halfway finished re-siding the house.  So half of the house has house wrap with new siding and the other half has no house-wrap, just old, rotted clapboards with splits and gaps, lots of air intrusion.  The siding won’t be finished until next year.  I could go on, but the point is that I wouldn’t want to design a system based on a present heat loss calculation knowing that the results are going to be very different as various projects get completed.   We just have to do the best that we can knowing that it’s ok if we get some things wrong and have to make adjustments later.  The energy efficiency of this house will continue to improve so there’s that.  So for now we are taking the simple approach of calculating BTU requirements for each room based on room size with the intent of zoning each room to make it easier to adjust whatever we need to later.  There is nothing from a design standpoint that we are doing now that we can’t change or undo later, other than maybe a few holes through the floor, but we can fix those.  

I would love to use some old cast iron radiators, and we may do so at some point in the future but for now I think we are committed to using slant fin baseboard mainly due to availability and ease of transport.  We don’t have a truck yet but when we do this will likely be something we pursue.  I will keep this in mind by running the supply and returns on the same side of the slant fin so we don’t end up with extra holes in the floor if we end up doing that later on.  

I think that’s it for now, I apologize if I missed anything.  I will circle back again soon.  Thanks again for the responses

hot_rod

Water jackets or inside HX are probably gone due to market needs and/ or liability issues. Always protect a HX with a safety relief valve. And dry firing them can lead to a big problem if water hits a red hot device. So a bit more than most people think about. Concept is simple enough, but it needs to have attention to detail.

!/2" copper will not allow much flow, if you use small tube, header it like this.

If you pipe like this, heat output can go directly to the load without need int to heat or travel through the tank.

I'm not sure you need the second tank however, unless you add an element for a second heat option?

My concern is if the stove will be able to keep up with what size load? Make the flow adjustable so you can gauge the heat output to keep the stove from condensing, forming creosote.

A protect valve at the stove hx could be another option, it automatically keeps the stove HX in a safe operating temperature range..

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Grallert

I would still do a heatloss regardless of future improvements. If you size the system to a worse case scenario you can always adjust water temperature as the envelope tightens up. It's rare to have too much radiation. Of course in your case too much radiation will have an effect on your wood stove rig with out attention and mixing of return water.

DCContrarian

It may be too late, but it sounds like you could have added 2" of polyiso foam under the siding without too much trouble. That would have made your house substantially more comfortable.

An ounce of insulation is worth a pound of hydronics.

leonz

You should seriously consider removing your wood stove and replacing it with a coal stoker stove to heat your home.

The only brands of coal stoker stoves I would recommend are Leisure Line and Keystoker

The return on your investment will be faster and you will have a continuous source of heat for your home, and it will require much less tending where you add rice coal once per day and empty the ash pan once per day.

The other option would be a fire brick lined wood and coal console circulator stove with shaker coal grates from US Stove.

Robert_25

For all the trouble it takes to harness heat from a wood stove into a hydronic system (and the poor performance) you would be better off installing a real wood boiler.

Cast iron radiators are often available on FB marketplace or local salvage yards. Used wood boilers often come up for sale as well.

A wood boiler installed in the basement and cast iron radiators throughout the house would really do the job. The best part is you can pipe the radiators (home run) so you can add them as you remodel the rooms.