Harmonizing wood stove and forced hot water heat

[illini81]

I have a 30 year old 2500 sqft colonial in Southeastern CT. The house is currently heated with a combination of electric baseboard (kids bedrooms) and a wood stove.

When we first bought the house, we were unsure if we would be here long-term. We knew the heating bills would be out of control (~5500/yr for electric and propane bill for prior owner, propane was used for hot water and a propane stove) We bought a wood stove as a bit of a hedge. In the event we left early, I figured it would pay for itself in about 2 years, so the project really wouldn’t be a loss.

However, in the event we stay long-term, which is now looking increasingly likely, the plan is to replace the electric baseboards with a better heating system. We will still burn wood, but not 4 cords/yr. My guess is that we’ll burn about half what we’re burning now.

So I’ve spent the past 2ish years off and on doing research on our options. It seems like there is no shortage of options, and each one has its pros and cons, as well as its supporters and detractors. Of the options we have considered, we have ruled out ductless minisplits and a ducted system. We are now leaning towards a forced hot water radiant baseboard system.

I like the idea of a hot water system because 1. Radiant heat is awesome, 2. The heat starts at the floor level, 3. I don’t have to worry about ducts in the attic, 4. It seems like it is easier to zone than with a ducted system (still possible but expensive). 5. Electricity is crazy expensive in CT, which eliminates ductless minisplits from contention

So after that long prelude, here is my question: Are there ways that I can optimize a hot water radiant baseboard system to work well with a wood stove? I have never had a system like this, but my understanding is that you don’t want the boiler to short cycle. Is it possible to mess with the temperature of the boiler? I’m thinking I could run it at a lower temperature when I have the wood stove going, which would keep the boiler running longer? Are there smartphone apps these days that can control boilers to this extent?

I’m assuming on this forum there are quite a few others who have forced hot water heat and a wood stove. Any tips you have on making the two work well together would be much appreciated!

 

[Brian26]

I am in CT as well. I invested in solar panels and mini splits. I pay just the electricty connection charge of $9.44 every month. CT has one of the best incentives for solar. I got $4k from the state plus the 30% federal rebate. So my 18k solar panels cost me about half that around 9k.

Mininsplits are insanely efficient. Mine spend most of their time running at around the equivalent of 600% efficiency. They absolutely crush every other form of heat most of the time in their efficiency with zero fossil fuels burned.

I dont even bother using my woodstove much anymore as the mini splits work so well and cost practically nothing to run.

 

[peakbagger]

First Question is have you had an energy audit done of the existing house.? It should include a blower door test. The audit generally will identify the best bang for the buck improvements. No sense in spending money on heating and cooling until you fix up the leaks.

Once you have the place tightened up then you need to get manual J heat loss calculation done for the house. This sizes the heating system you will need in the future. if you have a mortgage you need to system sized as though the wood stove does not exist.

The next big question is how much are you willing to spend?. Radiant baseboards cost a lot to buy and install. Far more than standard slant fin baseboard radiators. The standard recommendation these days is go with low temperature radiant emitters that can accept supply temps down to about 90 deg F (compared to standard baseboard that needs 160 to 180 deg F. . If you a have loose older home with older windows, you most likely will have to install near continuous strips of heat on the exterior walls. Radiant does not work well in a room without an open floor plan, This can be an issue with bedrooms where there is too much stuff pushed up against the exterior walls. Even if you have open floor plan rooms, the cost to retrofit a house with radiant will be quite expensive as fishing tubes through walls and between floors is not cheap. If you are a hard core DIY its not rocket science but it going to burn up a lot of time.

Where do you get your hot water from?. It likely that any solution for heating should include hot water. Its likely you will need a hot water maker type system with an insulated tank with internal coil that is heated by the new heating system. This ads 2K to the cost.

A wood stove is a space heater. It heats up some spaces well but the more remote spaces it does not work as well. Modern heating design is to multizone a house so that each space has its own thermostat, in the case of the wood stove zone, it will rarely run while the other zones will only run when there is demand for heat. There are a lot of variations but the two standard solutions are a central manifold with pair of pipes going from the basement to the room for each space. There will be thermostat for each room. This requires a place to run and hide the tubing and low voltage wiring which in most cases requires holes in the drywall or plaster to run the pipes. The other choice is larger zones with individual thermostatically controlled radiators that use Thermostatic Radiator Valves (TRVs). These have a thermostat on the wall but it controls the local radiator. There are pros and cons for each. Many newer high efficiency heating designs decouple the heating device from the heating system with an insulated buffer tank. Hot water for heating is pulled from the tank and then by use of temperature probes on the tank the heating source only fires when the tank temp drops outside of setpoint range. Realistically most new heating appliances are low mass units designed to cycle on and off so cycling it not an issue as long as the you have good controls. The nice thing with this option is you can hook up an outdoor air to water heat pump in the future and get rid of the fossil fuel in the future.

A swag for a reality check is if you need to buy a new boiler, and want low temp radiant budget 25K to 35K for a low temp system where you have good runs from the basement to the second floor. You can reduce the amount by as much as 10 K by going with regular high temp "Slant Fin" radiators. Many folks have lived with them for years and they work. Make them cold start with external hot water maker then add in an outdoor reset controller and the system is reasonably efficient.

For most folks this cost to retrofit means that its a lot cheaper to retrofit the home to allows the wood stove to circulate the heat to other rooms. Some appropriately sized ducts, fans and holes in ceilings can really make a lot of difference in moving heat around.

Now my editorial comment, unless you are climate change denier, the odds are highly likely that fossil fuels are going to be discouraged and the logical way to do that is tax them so that they are more expensive than no net carbon alternatives, wood is on shaky ground but electricity is potentially lower net carbon especially a coastal state like CT that is slated for gigawatts of offshore wind power. Public policy is pushing solar and minisplits and as Brian pointed out CT has some great subsidy programs for solar. You didn't mention if you have AC but expect most folks do in CT. A minisplit is far more efficient than a window unit and most large ducted heat pump systems. Youi can change the household heat pump to more efficient unit but rarely can you do much with the installed ductwork which usually is sized for low initial cost. Minisplits are around 3 times more efficient than baseboard for heat and as much as double compared to conventional AC. Put in solar and its hard to beat.

 

[velvetfoot]

We have a 2000' colonial with oil fired hot water baseboard. We also have a pellet boiler, but I haven't used it for a while because of the favorable oil price vs. pellets.

We have two zones, upstairs and downstairs. We run the wood insert constantly. (Maybe it's not as high output as your wood stove.) It heats the downstairs and some of the upstairs. There are two of us in the house. The (wifi) thermostats are set low-ish during the day, and 68 after five and before midnight. The oil heat typically comes on upstairs only between five and midnight. No downstairs, unless we've been away or something.

You'd think it'd be easier to retrofit hw baseboard nowadays with the advent of PEX tubing.

Are you in a neighborhood? You could see what your neighbors have done. Like, have they also retrofitted A/C. Maybe you could get natural gas-that would be awesome.

Being in SE CT, you could probably add some value to your house if you included A/C, like with a high efficiency heat pump or mini split.

Also, nowadays, air systems can be well controlled with motor operated dampers.

The quiet even heat of a hot water system is very nice though.

Look at the price of fuel. Propane around here was insane a little while ago-notsomuch now, I think.

PS: As far as the boiler running longer, for the pellet boiler I bought a highly insulated 120 gallon hot water storage tank for buffering purposes. It also has a stainless coil in it for domestic hot water. The tank is used when I'm on the oil boiler too. So, my oil boiler starts up once in a while and runs for a long time (not sure..an hour?) to heat up the tank to 180 or so.

 

[Brian26]

CT has tons of generous incentives and rebates available. Get the energy audit done as its basically free and inlcudes up $1500 in free work. They spent the whole day and sealed and insulated all my basement ductwork for free and a ton of other stuff. They did a blower door test and tested my ductwork CFM.

You can drive to any lowes or HD right now in CT and buy a heat pump water with an instant $750 rebate off the price right at the register. So you can get one for $350.

The energize CT program is flooded with cash. I probably have recived $10-12k in subsidies/incentives at my house. On everyones electric/gas bill their is a charge called combined public benefit charge to fund it.

Rebates and Incentives | EnergizeCT

Find information on Rebates and Incentives to help save money and improve your home.

www.energizect.com

 

[illini81]

Thanks everyone for the responses. I got an energy audit about a year and a half ago. The blower door test showed that we have a fairly tight house. The tech doing the test said that if we did any additional sealing, the air in the house wouldn't be replaced by outside air quickly enough.

Unfortunately our house is very shaded, so I don't think solar is a good bet for us, at least not at this point. Once I turn a few of our overgrown trees into firewood... solar might become a better bet

I looked into minisplits, but I am not confident they are a great option for us, due to our exorbitant electricity rates. I used the very handy heatcalc.xls spreadsheet here: (broken link removed) to compare the cost of minisplits with the cost of propane. I’ve attached an image with my inputs to the program.

When I plug in the appropriate variables for my situation (cost of electricity, HSPF estimate - note that per the spreadsheet, the HSPF # gets adjusted based on climate, cost of propane, efficiency of boiler), I find that baseboard electric costs me $64.48/Million BTU, propane would cost me $23.05/Million BTU, and ductless minisplits would cost me $34.92/Million BTU.

The idea that heat pumps aren’t exactly cheap when paired with the really high cost of electricity that we pay in this area jives with what I have heard from two people who have put them in recently – both were disappointed with their savings. To me, this doesn’t say anything bad about ductless minisplits – I think the technology is great. It just means that at some point, if electricity is expensive enough, the efficiency gains of the minisplits don’t cancel out the ridiculous electricity prices.

Anyways, so I look at the numbers in that chart and conclude that propane is the way to go.

 

[illini81]

First Question is have you had an energy audit done of the existing house.? It should include a blower door test. The audit generally will identify the best bang for the buck improvements. No sense in spending money on heating and cooling until you fix up the leaks.

Yes. Blower door test showed that we have a tight house.

Once you have the place tightened up then you need to get manual J heat loss calculation done for the house. This sizes the heating system you will need in the future. if you have a mortgage you need to system sized as though the wood stove does not exist.

A contractor I am working with is doing the manual J load calc, but I am taking no chances and will do the calc myself as well.

The next big question is how much are you willing to spend?. Radiant baseboards cost a lot to buy and install. Far more than standard slant fin baseboard radiators. The standard recommendation these days is go with low temperature radiant emitters that can accept supply temps down to about 90 deg F (compared to standard baseboard that needs 160 to 180 deg F. . If you a have loose older home with older windows, you most likely will have to install near continuous strips of heat on the exterior walls. Radiant does not work well in a room without an open floor plan, This can be an issue with bedrooms where there is too much stuff pushed up against the exterior walls. Even if you have open floor plan rooms, the cost to retrofit a house with radiant will be quite expensive as fishing tubes through walls and between floors is not cheap. If you are a hard core DIY its not rocket science but it going to burn up a lot of time.

Where do you get your hot water from?. It likely that any solution for heating should include hot water. Its likely you will need a hot water maker type system with an insulated tank with internal coil that is heated by the new heating system. This ads 2K to the cost.

Good question. I want to spend enough for a good system... without breaking the bank. What we are willing to pay depends on what we are getting for our money, so yeah. I don't really have a concrete answer yet.

As far as hot water - I am very interested in the heat pump hot water heaters. CT currently has a very generous $750 rebate for those right now.

 

[Brian26]

You have a HSPF number of 6.3 in your chart. Thats equivalent to like a 1970s heat pump. My Gree has a HSPF of 15.2. Put that in and see what you get.

Your gas and propane prices look off. The EIA has CT listed as a statewide average of 2.63 not 2. I think natural gas is like double of what the default 1.10 a therm thats listed. I have the same chart and thats a national average from a long time ago.

 

[illini81]

Now my editorial comment, unless you are climate change denier, the odds are highly likely that fossil fuels are going to be discouraged and the logical way to do that is tax them so that they are more expensive than no net carbon alternatives, wood is on shaky ground but electricity is potentially lower net carbon especially a coastal state like CT that is slated for gigawatts of offshore wind power. Public policy is pushing solar and minisplits and as Brian pointed out CT has some great subsidy programs for solar. You didn't mention if you have AC but expect most folks do in CT. A minisplit is far more efficient than a window unit and most large ducted heat pump systems. Youi can change the household heat pump to more efficient unit but rarely can you do much with the installed ductwork which usually is sized for low initial cost. Minisplits are around 3 times more efficient than baseboard for heat and as much as double compared to conventional AC. Put in solar and its hard to beat.

It is very possible that I could put in a propane boiler and associated hot water baseboard system, and the cost of propane could skyrocket due to additional taxes. I guess everything is a gamble to a certain extent.

Regarding cooling - we are fairly heat tolerant in the summer. We barely run AC. For example, my electric bill was $103 last June (no AC on), $102.5 last Sept (no AC or heat on), $121 last July (with AC), and $122 last September. In other words, I am paying about $20 extra during the 2 months of the year that I use my window units. So minisplits wouldn't really do a whole lot for me as far as cooling goes.

 

[illini81]

You have a HSPF number of 6.3 in your chart. Thats equivalent to like a 1970s heat pump. My Gree has a HSPF of 15.2. Put that in and see what you get.

Per the instructions in the Excel spreadsheet, the HSPF should be adjusted based on the region you are in. I am assuming the idea is that the efficiency of a heat pump depends on the outside temperature. A heat pump in Alaska is going to spend a lot of time calling for auxiliary heat than a heat pump in Alabama. I was assuming an HSPF of 9.0, which the spreadsheet adjusts to 6.3. If I plug in 15.2, the spreadsheet adjusts that to 8.0. That gives me a fuel cost of $27.50/Million BTU, which is still higher than the $23.05 for propane.

I am in CT as well and can assure you a good mini split will blow away both gas and oil. Also your natural gas price is close to double and propane is closer to 3 not 2 dollars.

I didn't adjust the natural gas price, because it is not an option for me. I currently have propane on my property for hot water, and pay just over $2.00. At higher volumes, I will actually be under $2.00.

 

[Brian26]

Per the instructions in the Excel spreadsheet, the HSPF should be adjusted based on the region you are in. I am assuming the idea is that the efficiency of a heat pump depends on the outside temperature. A heat pump in Alaska is going to spend a lot of time calling for auxiliary heat than a heat pump in Alabama. I was assuming an HSPF of 9.0, which the spreadsheet adjusts to 6.3. If I plug in 15.2, the spreadsheet adjusts that to 8.0. That gives me a fuel cost of $27.50/Million BTU, which is still higher than the $23.05 for propane.



I didn't adjust the natural gas price, because it is not an option for me. I currently have propane on my property for hot water, and pay just over $2.00. At higher volumes, I will actually be under $2.00.

One thing to keep in mind is electricity is very stable in price. The price is set every 6 months by the public utility comission. Its usually goes up or done a couple cents. Propane is volatile in price.

I have monitoring equipment on both my mini splits and achieve close to my HSPF number. Probably between 12-15.

 

[illini81]

One thing to keep in mind is electricity is very stable in price. The price is set every 6 months by the public utility comission. Its usually goes up or done a couple cents. Propane is volatile in price.

I have monitoring equipment on both my mini splits and achieve close to my HSPF number. Probably between 12-15.

That is certainly a factor as well. One thing I am considering is putting in both a hot water baseboard system with propane as the fuel, and a single minisplit in our combined dining room/kitchen/living room (same room as the stove). I would use the minisplit to heat the house above 45ish degrees. Even though the minisplit would of course be undersized for the house, there would be some temperature zone in which it could heat the whole house. And that would be the zone in which it is crazy efficient as well.

 

[peakbagger]

I sort of do that with my setup. I have baseboard fed by wood or oil as a backup with minisplit in the biggest room. We are in mild stretch up in NH the last two days so I am heating the house entirely with 12,000 (nominal) minisplit. Its not a big house but I am heating one entire floor plus half the second floor. A 12,000 BTU minisplit gets super efficient with higher outdoor temps and the output goes up. I think mine peaks out around 18,000 BTU. With some planning I can go down to about 35 F before I start loosing the temp but boy is it slow trying to bring the house up to temp.

 

[Brian26]

That is certainly a factor as well. One thing I am considering is putting in both a hot water baseboard system with propane as the fuel, and a single minisplit in our combined dining room/kitchen/living room (same room as the stove). I would use the minisplit to heat the house above 45ish degrees. Even though the minisplit would of course be undersized for the house, there would be some temperature zone in which it could heat the whole house. And that would be the zone in which it is crazy efficient as well.

Another huge plus with heat pumps are they are way safer compared to storing large amounts of flammable and explosive fuels in or outside your home. You also eliminate the fire and carbon monoxide risk. Propane can leak and literally level your house. Also there is essentially zero maintenance outside of cleaning your air filters and coil.

I would install a unit and see how it goes. It will no doubt save you a ton of money in mild weather. I orginally put a 12k unit it to supplement my oil furnace. I was so impressed I then installed a 2nd one and pretty much eliminated the oil furnace. In mild weather like today these things run at the equivalent of like 600%+ efficiency.