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Community and Q&A

Changing out a wood boiler to a natural gas boiler

Albert B. | Posted in Energy Efficiency and Durability on

Hello Group,

After stumbling upon this group while doing some internet searching, I came across an article posted by Dana Dorsett about condensing boilers that was very informational which led me to dig deeper into this GBA site and reading more articles. Now I’ve joined this group with the hope of seeing if I can garner some advise on a situation that I am trying to resolve.

But first a little background on the issue.

My father installed an indoor wood boiler about 15 years ago into his home to offset his heating requirements from a natural gas furnace in the house but also to mostly heat an addition he built on the east side of his home that was half of a four season sun room running half the length of his home and then a separating wall with a door into an attached greenhouse area where the wood boiler and an old slant fin gas hot water boiler as backup to the wood fired “dutch oven” style main boiler are located. The floors in both of these areas are concrete with hot water / glycol mix running through them for in floor heating with a forced air heat ex-changer as additional heating source if required for in the greenhouse area. There is also a heat ex-changer in the house installed in the ducting of the gas condensing furnace in the basement that heats the house with the furnace fan running continuously providing air circulation and heat from the wood boiler. The basement furnace in the house only comes on if the fire goes low or out in the wood boiler or if it can’t keep up at night which rarely occurs.

Now my father had a few huge covered greenhouses that he would pile his two foot length cut and split Tamarac firewood in. It got crazy hot in there in the summer time and dried the wood cork dry. At most times there was over 200 cord of dried wood in there that he would cycle through over about a five year period replacing every year the wood that was consumed with new wood and then moving into the next years supply the following year and so forth. Any wood that he burnt in the winter was dried for at least four or five years. This all worked fine for my parents for years until my father passed away suddenly at 80 years of age back in 2012. So my mother decided she would carry on using up the store of firewood until it was gone and then decide if she would sell the home and downsize or stay and figure something else out.

Well the time has now come that the firewood is nearly gone and she wants to stay as long as she can where she is because she is still in terrific health and loves working in her yard and garden in the summer time but the hauling of wood is getting a bit too hard for her now. She turned 80 this past January and has a very busy social life so she’d rather be out with her friends and not hauling wood. The whole home, sun room, and greenhouse wood consumption was around the 20 to 30 cords a season depending on how cold the winter was. So handling this amount of wood everyday was getting difficult for her and she’s asked me to see what I can do to help her out.

So what I’m planning on doing is making the area that is currently the attached greenhouse into sort of a heated work shop / storage area by removing the clear fiberglass roof and sheeting, shingling, and insulating it. This area currently houses all the boilers and I still need to keep some sort of boiler system here because this is the only heat source for the addition.

I can’t install an electric boiler as there isn’t enough available power in the home for one. There is only a 100 amp circuit coming in and the panel is already full with two sub panels as well. She use to have a gas hot water tank but that was changed out last year to an electric one when at the same time she had her old 1969 gas furnace removed and the new condensing gas furnace installed and they ran the venting PVC pipes up to the roof through the original chimney. So going electric boiler to heat the home isn’t an option without bringing in new power and replacing the panel and where that is located is way too much work and cost to consider.

So I’m thinking of removing both the Benjamin wood log boiler and possibly also the current Galaxy slant fin gas boiler that is used for backing up to the wood boiler, or just leaving it as is for a back up to what ever I replace the wood boiler with, and either installing a wood pellet boiler or a natural gas condensing boiler. Now gas costs going off her last gas bill are $3.98 per cubic meter. That is TOTAL cost after taking in the cost of the primary gas at $0.09 cents per cubic meter, supplementary gas at $0.15 per cubic meter, transportation cost for both the primary and secondary gas from Alberta to Manitoba and then the delivery costs through the pipes in the ground owned by Centra Gas to her. The gas itself is the cheap part where as the delivery and taxes are the costly part! Wood pellets around here go for around the $6.00 per bag mark. Now not having burned pellets before through a wood boiler, I have no idea of how many usable BTU’s can be obtained out of them compared to natural gas being used in say an approximately 90 to 95% efficient condensing boiler? I’m assuming less but truly don’t know.

So my question then is should I look at getting a condensing pellet boiler, a condensing gas boiler, or just forget it and stick with the backup gas boiler and make it into the primary and only boiler and to hell with it’s inefficiencies and just pay the higher gas bill for the next say 5 to 10 years that mom may stay at her home? I’m leaning more towards a gas boiler so it’s very hands off for her but she says she has no problems with a pellet stove as there is a large 30 x 30 foot area to erect a storage bin for pellets if need be if the price over the long term is significantly better than gas.

Then the next question I guess would be is how large of a gas or pellet boiler should be installed? The house is 1500 square foot bungalow with a basement and the addition is 1200 square feet. House is 1970 vintage with 2 x 4 construction so not much insulation in the walls. Ceiling has had upgraded insulation to R-60 so it’s good. Windows in the house and sun room are all triple pane argon filled so their good to. The green house has side windows that are two dual single pane sliders so not grea.t The walls are 2 x 6 construction and insulated in this area. The roof will be replaced with OSB and spray foamed and then drywalled for the ceiling so it’ll get to about an R-50 or so rating.Can’t use fiberglass bat insulation as there is no air movement up there as it’ll just be the 2 x 8 roof studs sistered together. and a center beam installed to help support the snow load.

I’ve been looking at the Viessmann and Froling lines and both look nice but definitely not stuck on them either way. Just that whatever I go with must be CSA approved for insurance purposes and have a decent presence in Canada and hopefully local as well. Just need to get it sized right the first time and not have it too large to prevent short cycling.

Another question I have is whether it’s any better to go with a gas boiler that modulates more than a 5::1 ration? Is it better to go with a unit that can do 10:1 or even higher? I realize that the efficiency will go down when it starts to really low fire but is the slight difference really going to be that significant when it starts to get warmer outside? Currently the wood boiler is setup to run at around the 120 to 130 degree Fahrenheit area which works for about 95 or better part of the time. Will going with a condensate boiler running at say a 90 degree rating make a huge difference? I’m thinking I’ll have to replace the coil in the plenum of the house furnace with a larger one to make this up seeing that most condensate boilers need to operate around that 90 degree mark to reach the point of some efficiency. I think the Viessmann 300 cu3a stated it is can go to 135 degrees but then I’m questioning how efficient it would be at that temperature as it probably won’t be doing too much condensing.

Anyways, this is starting to get to be real long and if anyone has continued reading up to this point they’re hopefully considering giving me their opinion! I’m sure that whatever responses I get will lead into other questions so I’ll stop at this point and see what happens.


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  1. GBA Editor
    Martin Holladay | | #1

    You've written a long novel, and most readers probably won't make it through to the end. Short questions are more likely to get answers.

    Here's my question for you: This homestead has been burning between 20 and 30 cords of firewood a year. That's a lot of BTUs. Does your mother plan to continue to heat all your greenhouses? Or will you be reducing the amount of heated area?

    If you need to burn enough gas to replace 20 or 30 cords of firewood each year, your gas bill will be quite high.

  2. Albert B. | | #2

    Hi Martin,

    Thanks for the advice.

    The greenhouse addition is not that large. About 25 x 20 feet. There was only the one. It will be converted from a greenhouse into a storage area and heated. Clear fiberglass roof will be removed and replaced to a conventional roof with insulation. The greenhouse area would have had about 95% heat loss during the winter nights. They grew plants in there and tulips so it had to stay around the 75 to 80 degree area. If the days were sunny then there was an abundance of heat generated through the fiberglass roof and the wood boiler only had to heat the sunroom and the house.

    Quantity of wood used was high because of the greenhouse addition. That would have changed to a lower amount when it is converted into just a workshop / storage area if she were to continue heating with wood which she wants to get away from because of the work involved.

    She typically likes her house at around 75 degrees all the time. That burns energy.........

    The other greenhouses where the wood was stored are not heated. My parents use to run a greenhouse operation until they retired and they kept a few of the greenhouses to store the firewood in. Now that the wood is gone I'll be knocking them down this summer and get them off her tax bill.


  3. GBA Editor
    Martin Holladay | | #3

    Do you have natural gas or propane? I'm assuming you are in Canada.

    Unless I'm having a problem with the math, your gas price seems about ten times higher than U.S. gas prices.

    If you are paying $3.98 per cubic meter, that means that you are paying $11.27 per 100 cubic feet (that is, per therm), or $112.70 per thousand cubic feet. That seems very high.

  4. Albert B. | | #4

    Natural gas. Yes in Manitoba, Canada. As I indicated in the original post, that price includes all the costs associated with getting the gas to the residence. The gas itself is the cheap part. The distribution is the expensive part. I’ll check her last months bill again to see if I read it wrong earlier and let you know. I remember seeing 9 cents for the primary gas and 15 cents for the supplemental gas per cubic meter. The rest was delivery and taxes.

  5. GBA Editor
    Martin Holladay | | #5

    According to this web page:

    Manitoba Hydro charges 37 cents per cubic meter for natural gas, plus a basic monthly charge of $14. So you are off by a factor of ten.

  6. Albert B. | | #6

    Hi Martin,

    Well I was over at my mothers place again to check up on things and looked at her gas bill again. Well I stand corrected as I had read her bill incorrectly and therefore calculated the numbers wrong. My apologize for misleading you and the group.

    Her correct rate from Jan. 11 to Feb. 14 is .2658 dollars per cubic meter of gas. So about 27 cents. There was a slight decrease in the rate during the billing period so there were two listed prices each for primary and supplemental gas charges.

    I should have double checked the numbers before typing them. 5.9322 and 593.22 cubic meters is a big difference when doing calculations!

    While I was at it I also looked at her electrical charges and they come all in at 0.0992 per kw/h and those are going up 9% very shortly.

    So her costs for last month was $137.86 for electricity, $158.51 for natural gas and approximately $700.00 on the wood cost that she burnt in her wood boiler. That wood price is based on what she paid for it about 4 years ago. Its currently going for $235.00 now.

    Just as a note, the gas she’s using is not for her living area but is used heating an out building and will still be there no matter which way she decides to change to from wood.

    Thanks for correcting me.

  7. GBA Editor
    Martin Holladay | | #7

    I'm assuming that your $6 bag of wood pellets holds 40 pounds of pellets. Since wood pellets have 8,250 BTU per pound, each bag has 330,000 BTU of fuel.

    So 100,000 BTU of wood pellets cost you $1.98.

    Your natural gas is costing you 27 cents per cubic meter, which means that you are paying 76 cents per therm. (A therm is 100,000 BTU.) So the pellets are 2.6 times more expensive than natural gas.

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