OWB retrofit to abandoned hydronic baseboard system

Wahoo · November 9

I bought a house in central Virginia a year ago. 1900's farm house. ~3000 sqft, two stories, stick-built, been decently renovated over the decades (new windows, siding, HVAC etc). Currently heats with a dual-fuel heat pump that was installed in 2015-ish. Ate us up with electric and propane costs over last winter; about $5k over the 5 months we heated. Really untenable.

In the basement there is still a propane boiler that was disconnected and abandoned that was hooked to a baseboard radiator system throughout the house. I am unsure of the date or reason for disconnection. Two zones (up/down), pump, valves, etc is all still intact...and in fact, the radiators are still holding pressure on the gauge on the boiler.
I am installing an outdoor wood boiler with the desire to tie-into the baseboard radiator system. Here is where I have struggled to find competent local knowledge on the best way to do this.

My idea is to have closed loops from the boiler and baseboard systems exchange through an appropriately sized plate exchanger (I was told a 5x12 70 plate would fit my needs).

My questions are as follows:

Is this system the best way to tap into my existing baseboard radiators?

In my case, is it really as simple as installing the exchanger and replacing the pumps/thermostats valves etc?

Do I need a "buffer" tank on the radiator side of the exchanger to help with heat speed and fuel consumption?

What other misc items would you include in a system like this to really make the most efficient and reliable system? (The existing old pump is a B&G NRF-22—should I make use of the deltaT new pumps Taco has?).

One last comment, I want to say that forums like this are such an incredible resource but unfortunately becoming less and less common as tech companies find ways to monetize our data. Thank you for being part of keeping "the old internet" alive!

hot_rod · November 9

I would pressure test the baseboards first to be sure you have a workable system.

Most OWF have enough fluid capacity to not need a buffer.

Yes a plate HX is the best way to separate the open and closed loop systems.

Spend the $$ on a good insulated piping system. It needs to be 100% water tight.

How many feet of baseboard? That will tell you the amount of BTU you need to size pumps, piping, etc.

Jamie Hall · November 9

@hot_rod , who knows as much about these things as the rest of us combined, has got it on the heating and house side of the equation.

The wood boiler, however, is another matter. Be sure and get really competent advice on setting up and plumbing the specific boiler you pick. At the very least, for a wood boiler you need a dump zone for when (not if) it runs away on you, and — in my view at least — that needs to be arranged in some manner so that it is operational in the event of a power failure.

Another point is that it won't save you overall on BTUs. The house doesn't care where the heat comes from! So do some figuring to find out how much wood you are going to need — and where you are going to get good quality hardwood firewood, seasoned at least two years. Figure on about 24 million BTU for a cord of hardwood. You can look at your bills from last year to estimate how many BTUs — and thus cords — you need per year (for reference, a cord of wood is more or less equivalent to 170 gallons of fuel oil or 270 gallons of propane).

hot_rod · November 9

on a good day the basic OWF run about 40% efficient. The gasification units are much higher. So they eat a lot of wood , and can smolder when the heat load drops

If it is an unpressurized type they just boil over as their over heat protection😉

You will learn how to load it based on weather conditions

GroundUp · November 9

Assuming this will be an unpressurized name brand OWB, you will not need any sort of buffer nor a dump zone. All factory built OWB have ample onboard storage, and IF (not when) they "run away", they simply boil over and that's that. Cut into the return pipe to the gas boiler and insert plate exchanger (size may vary based on actual BTU and temp requirements, but a 70 is almost certainly adequate) there to preheat the return water before it enters the gas boiler. Run the OWB loop 24/7 and everything else inside can stay exactly as it is if you don't intend for the gas boiler to be a operational. If you do, you'll want an aquastat on the OWB supply line before the exchanger to kick the gas on when water temp falls below setpoint. As Hot Rod said, spend the money on good underground lines (NOT the drain tile wrapped junk) such as Thermopex, Rhinoflex, Insulpex, or Logstor. What model OWB would you be using and what is the distance from it to the heat exchanger's location?

hot_rod · November 9

Two piping options here. Both put the back up gas boiler as a parallel load. No flow goes thru it when the OWF runs, just directly from the OWF, through the HX, to the radiators.

Simple piping is fig 5 is the HX connected to the OWF, the boiler and load on the B side of the HX. In this arrangement the OWF pump runs all the time.

Option 2, fig 5.10 shows a shunt pump that flows some heat from the back up boiler to prevent the OWF from freezing if you are not around to fire it in freeing conditions. You have less heat loss to deal with also if the OWF pump doesn't need to run 24/7. But more complex piping and control wiring.

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vtfarmer · November 9

Something isn't adding up, do you have a duct sealing or similar issue causing you to lose a lot of heat from the building envelope? I bought a 6,500 square foot house in west-central Virginia (western Augusta County) in 2021 that's heated with four heat pumps and my utility is Dominion (10 cents/kWh in the winter) and my electric bill never went over $500 in a given month even during the crazy cold spell we had at Christmas a couple of years ago. Granted, this house was built in the early 2000s so it's pretty tight compared to a 1900s farmhouse, but not enough of a difference to account for the cost you're seeing, I wouldn't think.

Have you done a heat loss calculation for the home and do you know what the point where your system switches to propane is? My hypothesis is that you have unaccounted for heat loss and something strange with your LP cut-over threshold.

leonz · November 10

I hope you have not purchased the forest eater yet.

A bituminous coal stoker will provide better heat with less work.

Wahoo · November 11

I apologize for the delay in getting back to ya'll…busy weekend.

I just measured (again to double check) the lf of baseboard in the house.

I have 64' on the downstairs loop and 56' on the upstairs loop. (So 120' total)

I also should have been explicit that the propane boiler is completely disconnected from any gas or electric lines and I have no desire to fiddle with the thing again to be honest. I would love to just utilize the lines and remove the boiler altogether. I did try to have a tech come out and pressure test the system but he just tapped the pressure gauge and said there's no need…

@GroundUp I bought 80' of thermopex ($15/ft 😬) but boiler will only sit about ~65' from house

@hot_rod I appreciate the diagrams I assume I can just get away with the same system minus the "aux boiler" as in option#1? Also, I have the heat pump as backup for weeks where we are away and traveling for extended time, but as you brought up, that doesn't solve my freezing OWB line issue…is there any reason I shouldn't use glycol on just the outdoor loop? The boiler I have on order has a 60gal capacity plus whats in the lines to the HX. I have heard glycol breaks down when heated, should I prepare to replace or boost it yearly if i go this route?

@leonz & @GroundUp I have landed on a Portage and Main "coal" shaker style boiler. It has a pretty unique firebox as the lower portion is firebrick (replaceable) and the boiler jacket is just at the top half of the fire box and around the double pass chimney. This video (https://www.youtube.com/watch?v=udibSDcUv2o&t=11s) is a pretty interesting comparison.

Here is my parts list so far:

4900 series Taco air separator

Caleffi DIRTMAG

5x12 70plate HX (https://altheatsupply.com/products/70-plate-water-to-water-heat-exchanger)

I'd think I'd like to use a deltaT pump like a Taco vt2218 but I am wondering what are the pros and cons of using a pump for each zone vs one pump and 2 zone valves (Taco Sentry etc). Does using a deltaT pump in the 2-zone valve configuration affect the performance or accuracy in any way?

@vtfarmer When I first moved to VA I was living in Deerfield…gotta be close to where you are :) I'm in Scottsville now. I do think there was some user error with the way we were controlling the heat in the house, which probably led to over-consumption of propane. We were given nothing from the previous owner regarding home systems or "this does that". so we have been figuring it out as we go…

hot_rod · November 11

no you don’t want to use glycol in an open system. It goes bad quickly when exposed to the air. Plus the overheat protection sometimes involves the fluid boiling over, you don’t want to put glycol through that either.

So either someone keeps a fire going when you are gone, you drain it, or have a method to keep the water moving. If you run the boiler pump to keep water moving when the fire is out, you don’t want to run the house pump🤔

To me a delta T pump operation is a limiting device, it allows the pump to operate at a constrained delta, even when the system prefers not to operate that way.

Hydronic heating systems are a dynamic system. They can, should change the heat delivery as the load changes. Big cold loads will drive a wide delta. As the space warms, the load lessens, the delta closes up. With 120 gallons or more fluid capacity, short cycling should not be an issue.

A delta p circ with zone valves is my preferred method.

A Caleffi DiscalDirtMag is another option, 3 functions in a single device.

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vtfarmer · November 11

Deerfield is indeed only about half an hour from me! I am outside of Churchville. User error may play a small factor, but given that I can keep this large house at 70 all winter using heat pumps with the cold winds up here in the hills and only spend an additional $100-300 per month on electricity makes me worry that something else is at play for you.

I will add that when I lived in southwestern Vermont before moving down here to VA I had a newer gassifying OWB and it ate 12-15 cords of split, dried wood per winter to heat a 2600 sq ft house plus 600 sq ft apartment built into the barn plus domestic HW. I felt pretty clever when I set it up, but I was happy to be rid of the burden of feeding it when I left!

GroundUp · November 11

I too would omit the delta T circ in favor of a delta P or even just a regular old 15-58 sized circ or two, pr just leave your existing equipment in place minus the boiler if you want it gone. Glycol is not a good idea for a system like this for the reasons HR mentioned above, and when it goes bad it becomes acidic very quickly which a P&M will NOT tolerate, being mild steel construction. If you plan to shut it down for an extended period of time during cold weather, draining it would probably be the best option but if you leave the OWB circ running, there will be some residual heat picked up from the house and sent back out to the OWB to prevent freezing. If you are buying factory direct, you will have NO support from Brian after the sale is made- this has been a very well documented problem with P&M. If you have a local dealer, please disregard the above. Being in VA, I might suggest giving Eldon Yoder a shout and taking a look at the Heatmaster C150 to compare to the P&M BL2534 you're looking at. They're much more refined than the Ultimizers, and built from 100% stainless. Plus Yoders have a great reputation for taking care of their customers unlike most Portage and Main dealers. If you're looking to get rid of the gas boiler, Bob's first drawing would be pretty close if you skipped the aux boiler portion and moved the circ & expansion tank to the supply side. Regardless of which OWB you choose, they need to have a lot of flow to stay happy so you're going to want something like a Grundfos 26-99 on the OWB circulating 24/7 through the HX, or a smaller 15-58 flowing through the HX and a second one just mixing the water jacket. The cabinets are a real pain in the butt for piping on the P&M as well, where the Heatmaster is wide open.

leonz · November 11

Avoid portage and main like the plague,

a Maertons coal stoker boiler is what you want for burning sub bit, bit coal and lignite, it will cost a little more for the freight but they have a good coal stoker based on the Iron Fireman design with a separate combustion air pipe system like the Iron Fireman coal stokers that were built in Spokane, Washington.

Wahoo · November 14

Thank you all for the help. I will post some pictures of the final install. I am going to go with @hot_rod recommendation of a DeltP circ with zone valves on my 2 zones.

Last questions (hopefully):

Do you have any recommendations on the brand of Delta P pump & size to replace the NRF22? Should I oversize a bit?

The two zone valves are shown in pic below (Honeywell v8043f1051)

Should I match brands with the circ pump? What would your recommended valve be here in my case?

Again, thank you—I'm a roofer so it has been very interesting to learn more about this trade.

Ironman · November 14

I’m near Staunton and I specialize in Hydronics including outdoor wood boilers.

P/M me if you want help.

leonz · November 14

What brand of forest eater did you buy?????????????

hot_rod · November 15

https://forum.heatinghelp.com/discussion/comment/1820180#Comment_1820180

I like the Grundfos Alpha circulators. All brands have similar styles, Taco, Wilo, B&G, Aquamotion.

OWB retrofit to abandoned hydronic baseboard system

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