Click here to Find a Contractor in your area.
In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Need to contact us? Visit

Need advice on converting from oil to natural gas biolers...

EdgemanEdgeman Member Posts: 15
Oil prices are killing me and with all the incentives and rebates out there, it is time to switch to natural gas! I spent the last few week reading a ton of info on the internet. I live in a coastal CT town in a 1960 sq. ft wood shingled raised ranch with a timberline asphalt roof. This week I had an energy audit done. My oil boiler is a 25 year old Utica 122K BTUs which runs at 79% efficiency as per the energy audit with 3-zones but on eis slaved into another so I have 2 thermostats. With the blower door test the infiltration was reduced from 4470 to 3830 CFM. The SlantFin heat loss calculated at 41,200 BTUs with a 9 degree design temperature. There are 4 people living in the house and the coil in the oil boiler is inadequate and has been a pita.

What size gas boiler should I look for? Do i have to size up the boiler for hot water? A couple of contractors have suggested a Navien CH-210 Combi with the tankless HW. After reading comments I am not sure about the reliability and maintenance cost of the Navien. I am thinking of a high efficiency gas boiler AFUE 90%+ for the rebates and operating cost mated with an indirect-fired water heater. What size gas boiler and indirect tank should I get?

Does the 41,200 BTUs heat loss sound correct for my size house? Do I have to increase it for indirect hot water heating? One contractor suggested a 96K BTU ballpark whereas another proposed a 175K BTU Navien CH-210asme Combi. Am I underestimated my heat loss?

Any suggestions and comments are greatly appreciated and I will be speaking to contractors this week. Thanks.


  • SWEISWEI Member Posts: 7,356
    41k heat loss

    would lead me towards a Triangle Tube PTS60 (or a Lochinvar WHN055) paired with an appropriately-sized indirect.  Increasing the size of the indirect should cover the DHW demand unless you have extraordinary DHW loads like a giant soaker tub (and there are better answers for that than an oversized heating boiler in my book.)
  • Paul48Paul48 Member Posts: 4,256
    Thinning the Herd

    If a contractor doesn't do his own heat loss, don't use that contractor. Don't use a contractor that wants to over-size a mod/con for DHW.What type of emitters do you have....copper fin-tube, cast iron radiators? With a small load like yours, keep it simple. Run it as one zone with ODR. Splitting the home into small zones just makes the work of the mod/con harder.Keep in mind, the mod/con relies on cool return temps to run at the most efficiency.Bedrooms can use TRVs, if  you like sleeping in cooler temps.

    One of the most important things,is to have included in the contract that the boiler WILL be installed according to the manufacturers instructions.Prior to installation, get the boiler manual online and familiarize yourself with the proper installation.

    Beware the "Fast Shuffle"....If a contractor can't slow down to discuss your system and your concerns, use extreme caution.

    Beware the "Switch-a-roo"....Verify the contractor is installing the agreed upon boiler, and not just a larger boiler because it was in stock, and yours wasn't.
  • heatpro02920heatpro02920 Member Posts: 991
    Do the math... before going Mod/con..

    I have a few posts on here explaining on how to figure out if a mod con is worth the extra expense and most of the time in a low BTU situation it is not....

    If you were my customer I would recommend a Weil McLain CGi-3 {I have great luck woth these little boilers, this on specifically can get really good efficiency 85+ with out much work... and the heat loss is rite where you are 45K out...

    Then I would install an on demand tankless water heater, I like the Rinnai RU80 or ru98 depending on your needs, the prices are very close but if the 80 meets your needs at your temperature rise I would go with the 80, if you need more go with the 98....

    Your initial investment will be much less and you will have 85% c. eff. for heat and 95+ c eff. for DHW... and for a little more system efficiency you can install Delta t circulators and an aquastat with Outdoor reset capabilities... Plus programable thermostats won't hurt...

    The issue is making sure a mod con pays for itself at the minimum, because most likely it is going to last half as long and have twice as many service issues that a standard boiler... And because you wil probably only save 10% {maybe} over a properly installed cgi3 with ODR with an on demand tankless, so with your heatloss say you spend $1500 per year for heat and hot water, you will save $150 per year by installing a mod con, but its going to need replacing and service far before the standard unit will so you will eat that $150 up in no time... plus keep in mind most mod con installs cost more than double a standard boiler..,.,, All money you will never get back... Now if you were spending $5000 a year for heat and DHW, 10% is $500 and you can justify it a little better....

    So anyway if you are stuck on a mod con {Don't get me wrong they are pretty, and I have one in my house} go for the TT solo 60 with an on demand tankless...
  • EdgemanEdgeman Member Posts: 15
    mod-con is the way to go...

    All the incentives are geared to the mod-cons. $750 rebate for 90% AFUE from CT Gas, $350 rebate from CT L&P, $750 rebate for Indirect or Combi, plus 2.99% for 10 years! If will be cheaper than what I am paying for oil without any up front cost. Also if i go non-con, I have to perhaps re-line the chimney for $1500 as gas exhaust is much cooler than oil which drafts better. It's a no-brainer, the feds and the northeast states want houses to be off oil.

    One contractor is proposing a Navien 175BTU CH-210 Combi with tankless DHW or for $1000 more a Weil-McLain GV90+5 140BTU mated with an AquaPlus 55 Indirect. I'm think i can scale it back to a Weil-McLain GV90+4 105BTU with an AquaPlau 45 to cut the cost? He suggested the tankless and I suggested a pricing for an indiret instead.
  • Paul48Paul48 Member Posts: 4,256

    Don't over-size the mod/con. It will short cycle. Sizing is absolutely critical.
  • heatpro02920heatpro02920 Member Posts: 991

    Do you have any links to them rebates? I own a house in CT also and haven't seen all of them.

    As far as using the chimney the Cgi3 does not vent have to vent through the chimney and you can side wall vent it, and since you can equate plugging up the chimney to 5% fuel savings this is one of the factors helping with the mod-con vs standard units...

    The rebates I see people getting are around $750 but you are talking an average additional $6-10K for the installs...

    And you can not ignore the service and life span advantages...

    That being said my home has a mod con and propane at that lol {if you don't save in the long run with NG, than propane may cost you money in the end with NO rebates} But I am in the field and having the equipment I sell in my home helps with sales, the other factor is my unit is heating over 4000 square feet, but when you have such a low heatloss even with the rabates, its hard to recover your costs...

    You have lbviously made up your mind, and you wont be disappointed with a TT 60, that is for sure BUT, other people that research the topic may find this information useful, and if you get an installer that takes pride in his work, you can not beat the aesthetics of a well done Mod con, I paint my back boards flat black and paint the unistrut white, then polish the copper when everything is done, they can be quite impressive that is for sure...

    I am going to start offering aluminum back boards too and paint the strut black...
  • EdgemanEdgeman Member Posts: 15

    The link for the rebates are at CNG or your gas company under converting to natural gas. The rebates are geared to replacing old inefficient boilers with mod-cons with a AFUE of 90%.

    I counted that I have around 160 ft of baseboard in my house. A contractor said that if I multiply that 160 x 560 = 89,600 BTUs that would be the maximum BTUs that can be outputed. Is that true? Another contractor who seems very knowledgeable is suggesting the TT Prestige Excellence PE110 boiler with internal indirect hot water heater. He likes it better than the TT Challenger Combi for hot water generation and thinks it would be more reliable than the combi.
  • SWEISWEI Member Posts: 7,356

    Is a fine boiler if you have a heat loss of 80-100k and your DHW needs can be met by its 14 gallon indirect.  It is NOT a good choice if your heat loss is 41k.  Really.

    DO NOT OVERSIZE YOUR HEATING BOILER.  Any contractor who tells you this is a good idea should be shown the door.
  • heatpro02920heatpro02920 Member Posts: 991
    edited February 2013
    Just curious for my customers sake...

    I tried looking, but the clp mostly say they ended 2012, except the heatpump water heater says 2013... I haven't gotten any info for what they are doing this year, RI {national grid} sent me a list, but not CT...

    And if I were you I would take the advice of the guys on here, Swei is correct, DO NOT oversize a mod/con, you will be unhappy with the result...
  • EdgemanEdgeman Member Posts: 15
    The rebates have been extended through 2013...

    Look on the CT Natural gas site.

    How do I calculate heat lost base on oil consumption? My energy audit says in 2012 I used 775 gallons of #2 diesel at 79% efficiency. The gov data says that my region had 4753 heating degree days in 2012. I keep the house at 68 degrees. How do I estimate the hourly BTU heat loss from this data?
  • R ManninoR Mannino Member Posts: 422
    You Asked

    I had condensed Brad's formula for my own area (Long Island) with average DD so as to simplify the equation. On Long Island with older lower efficiency equipment and a winter with average DD and a "normal" delta T if you multiply the gallons used by 55 gives you a rough heat loss estimate.
  • Paul48Paul48 Member Posts: 4,256
    We Have A Winner!

    That's 42625.......That's almost a match for his 41+ change slant/fin heat loss.
  • heatpro02920heatpro02920 Member Posts: 991
    heat loss is heat loss, the math won't lie...

    I would shoot for a unit between 38K and 45K....

    With such low losses, I usually add a little BTU for DHW if you are going with a larger tank...,

    I think the most important thing is to get a contractor out there to recomend what he thinks you need... If he comes in and says to get a 100K BTU boiler and doesnt perform a heat loss than move on, free estimates don't cost anything but your time... You will find one...
  • EdgemanEdgeman Member Posts: 15
    Applying Brad's formula:

    BTHU = (Annual Fuel usage/0.6)*(house temp-design temp)*efficiency*fuel heat value)/HDDx24


    68 house temp that we set to

    9 design temp from gov data

    0.79 efficiency from energy audit

    138690 fuel heat value for #2 diesel

    775 fuel usage from energy audit/oil company logs

    4753 Heating Degree DaysHDD from gov

    yields = 73,197 BTU loss per hour
  • R ManninoR Mannino Member Posts: 422
    I Concur

    with Heatpro. The bigger problem is finding a boiler small enough.
  • EdgemanEdgeman Member Posts: 15

    Looks like I'm looking at the TT CC125s (aluminum heat exchanger) with the TT Smart 40 Indirect Hot Water Heater vs. Weil McLain GV90+4 with the Weil McLain AquaPlus 45 Indirect hot water tank which is 5% cheaper. The GV90+$ has a cast iron heat exchanger. Will this have a longer life? Which one would you choose. The contractors are suggesting the the TT Prestige 60 is too borderline with the indirect tanks. Thoughts?
  • Paul48Paul48 Member Posts: 4,256
    TT Prestige 60

    With priority domestic hot water. I'd either increase the size of the indirect if needed, or add storage.A cheap electric water heater(not wired) works just fine as a storage tank. I believe icesailor refers to it as a "Third World" indirect. I would not oversize the mod/con.
  • SWEISWEI Member Posts: 7,356

    Is massively oversized for your heat loss.  Its minimum firing rate is 33k, meaning it will be short-cycling the vast majority of the season.

    DO NOT OVERSIZE YOUR HEATING BOILER.  How many times do we have to repeat this?

    Paul48 gave you the correct answer.  If your contractor disagrees, find another that has real hydronics experience.  If you have a huge soaker tub, consider using a properly-sized tankless water heater as a booster.  No need for a condenser there as it should only fire when the tub is used.
  • Paul48Paul48 Member Posts: 4,256
    edited February 2013
    Read This

    and if need be, we could begin posting links to 1000 threads from folks that have over-sized their mod/cons.

    Beware the "Fast Shuffle"....."Let me handle it, I know exactly what I'm doing"."I've installed a thousand boilers".........One other mod/con. Check out some of their other mod/con installs.
  • EdgemanEdgeman Member Posts: 15
    Good article...

    I see said the blind man. I will have them configure the TT Prestige Solo with the TT Smart 40 Indirect Hot Water Heater.

    I currently have a propane stovetop which uses maybe 30 gals a year @ $4.33 currently.or $130 per year. I also have an electric clothes drier. Should i bother piping natural gas to change the stovetop and perhaps have a gas drier if ever my electric drier dies? It cost $500 to run the gas lines on the outside of the house to hook up the stovetop and have the ability for the gas drier later. Is it worth it? Not sure what the equivalent cost are but if natural gas is 1/6th of the price of propane then the payoff is 5 years. Should I bother or keep the propane? My Maytag electric drier never dies.
  • heatpro02920heatpro02920 Member Posts: 991
    I don't know how many times we can say

    Don't oversize mod cons. I a have a customer that I inherited that has 2 hydro air units 3 tons each, with a gb160 that is all of 3 times the heat loss, I put in tstats with adjustable diffs, buffer tank, indirect ( they needed a water heater anyway) and up sized the circs as well as turned their fans on high heat and that thing still only runs about 8 minutes at a time.. And in my experience hydro air units always return cold when properly ducted and sized....
  • Paul48Paul48 Member Posts: 4,256
    My Opinion

    I like gas stoves, and would not want to deal with propane. I wouldn't have a gas dryer in my home. Lint and flames don't mix. Too many fires are caused by them, for my liking.

    Download the I&O manual for the TT60, and start familiarizing yourself with how it is supposed to be installed. The contract must state that the boiler will be installed to manufacturers specification.
  • EdgemanEdgeman Member Posts: 15

    One contractor said that with the TTPrestige 60, "you don't have enough BTUs to meet minimum flow rates. You're going to need at least 110k." On the spec sheet of the Smart 40 indirect, it says "Boiler Output BTU/Hr = 112K BTU. Does that mean that I need 112K BTUs from the boiler to get the spec 1 hr recovery of 180 gals, continuous flow of 150 gals, and peak flow of 5 gal per min? Will the TT60 impair the recovery heating rate of the Smart 40?
  • Paul48Paul48 Member Posts: 4,256
    No Go

    The 60 is a no go with the Smart 40. Still can't throw the baby out with the bath water, and over-size. You have to pursue other options. Heatpro mentioned a tankless on-demand with the TT60.
  • heatpro02920heatpro02920 Member Posts: 991
    Paul is 100% correct

    tt60 with smart 40 is not a good idea...
  • SWEISWEI Member Posts: 7,356
    Indirect sizing

    The 112k number you see in that chart represents the maximum number of BTUs the SMART can transfer.  A boiler with a lower output reduces the continuous output rate of the system.  A boiler with a higher output either downfires to 112k or short-cycles on DHW calls.

    A PTS60 will heat 1.4 GPM @77F rise continuously.  It only produces 54k, which seems small when you look at tankless or combit outputs, but still nearly twice what a conventional tank heater puts out.  The secret is the tank sizing.  If the math tells you to buy a 50 or a 60, do it.
  • EdgemanEdgeman Member Posts: 15
    edited March 2013
    So to compensate?

    So you're saying, if I understand you correctly, I should increase the Smart to a 50 or 60 to have more on reserve to compensate because the PTS60 can only produce 1.4 gpm in the dead of winter? Then I won't suffer short cycling if I were to step up to the PTS110 instead?

    Or can I set the temp to 160 degrees in winter on the Smart 40 to compensate. The specs says it can be set to 180 degrees in their stainless tanks.
  • SWEISWEI Member Posts: 7,356
    compensate for what?

    Has someone done a DHW demand calculation? 
  • heatpro02920heatpro02920 Member Posts: 991

    you are not really on the correct track, here...

    #1- I would get the 110 rite out of your mind

    #2- THE TT60 and smart 40 most likely will not give you a satisfactory recovery of hot water.

    #3- get us an approximate dhw load {just add up all the fixtures that will demand at one time in gpm and we can figure out your indirect sizing, im guessing a 60 with the 60...

    You have other options like on demand tankless, or potable storage. Is there a specific reason you will not consider a tankless rinnai or other brand?
  • EdgemanEdgeman Member Posts: 15
    edited March 2013

    My hot water demands are not extravagant. We have 4 people in the house and 2 baths but one only has a shower. 3 people will shower in the morning but not at the same time. I shower at night. The shower heads are High Sierra 1.5 GPM High Efficiency Low Flow Shower Head (highly recommended by the way). Wifey said that the new shower heads were stronger and better than the 2.5 gal heads I replaced. The Gaggenau dishwasher will run at night. Then there's the standard Maytag washer, 4 loads per week. My view is colored by the crappy coil in the oil boiler we currently are living with. It can't feed one shower so I will catch all kinds of hell if we upgraded and run out of DHW.

    I am shying away from the tankless because of reliability, consistentcy, low flow HW. I like the indirect HW for simplicity and longevity.
  • heatpro02920heatpro02920 Member Posts: 991

    water heaters last a long time, I have seen many more indirects fail than tanklesses, and when a tankless fails it can be repaired most indirects that fail get replaced... Rinnai has a 12 yr warranty, I have installed a lot of them with great results...

    Not running your new boiler will also extend its life, not heating 60 gallons of hot water to 140 degrees will save your wallet some stress too. The initial costs are similar and in your case probably less...

    In my own home I have a rinnai ru98i installed my house has 4 full baths is well over 4000 sq feet with a diva wife and 2 sons that seem to be in the shower long enough to write a short mystery novel, and we never have any problems, we have had 3 showers running and the wash machine at the same time with no low flow heads.... I would seriously consider one, they are worth a look for sure...
  • EdgemanEdgeman Member Posts: 15
    edited March 2013
    And the winner is...

    TT60 with a Smart 40! Thanks everyone for helping me with this confusing decision.

    Now upon oil to gas conversion, getting rid of the 275 heating oil tank?

    The 5 year old 275 gal heating oil tank is above ground and in a shed next to the driveway. The gas contractors are quoting me anywhere from $500 to $750 to remove it from my property.

    Being that it is above ground, is it ok to put on on craigslist list to get rid of it? The previous owner had to remove the in ground tank when I bought the place 5 years ago. He had the new one installed. I figure perhaps i can sell it for $100 or at least give it away to avoid the onerous removal fees. The town only has restrictions and laws for removing in ground oil tanks. The tank looks new and i expect i to be near empty in mid April when I do the conversion. There is currently 140 gals to get me through 6 weeks in coastal CT. Thoughts?
  • EdgemanEdgeman Member Posts: 15

    Most of my contractors are insisting on the TT110 rather that the TT60.

    "The 110k will not Short Cycle it is designed to modulate, these boilers run on low fire 80% of the time. You will need 110k BTU with your hot water demand setting the tank high will causing scaling and other problems. We have been designing systems for years and are good at it, we also see a lot of poor designs."

    "We don't set up the boiler with priority, as you may now, when the hot water demand is calling the boiler will not produce heat for the home. I also seen in the past in the event the hot water heater malfunctions for example, if the pump fails the demand for hot water will never be satisfied therefore the boiler will not switch over to heat. The same goes true if the aqua stat fails on the water heater the boiler will never switch over to producing heat. Having siad that if you insist and you want the TT60 I will quote it for you. I feel very comfortable and confident with the 110, it will not short cycle due to the turn down ration, but I want to make sure you are happy. I will email you over the quote for the 60 on Monday."
  • SWEISWEI Member Posts: 7,356
    edited March 2013
    minimum firing rate

    on the PTS110 is 30k.  On the PTS60 it is 16k.  Using 95% efficiency, those translate into 69.5% and 37% of your worst case heating load, respectively.  Which one do you think will have longer burn times and less short-cycling?

    The second bit of advice sounds as though it came from someone who has not been through the TT factory training.  The PTS boilers come with a temperature sensor which replaces the aquastat in the SMART indirect.  This allows the boiler controls to make more intelligent decisions about when to send heat to the indirect. There are control settings which limit the amount of time a DHW call can have priority which also factor into this.

    You should ask directly if they are factory trained for two reasons.  First, you want someone who really knows the boiler and the controls, and second, they receive special (low) pricing on extended warranties for residential installs.

    Did any of your contractors suggest the PTS60 up front?  I'd lean towards one of them rather than having to argue with someone who knows less than you now do about boiler sizing.
  • RobGRobG Member Posts: 1,850

    No contractor would want to under-size your boiler. They would end up replacing it at their expense. Therefore most (not all) will try and oversize the unit (they don't pay your gas bills and you will still save money over your existing system). It's a win , win on their part. A proper heatloss will actually slightly oversize the system to take into account for human error. Trust in the heatloss!

    The worst case (if undersized, which I doubt) is that on design day you might only be able to keep your house at, say, 65 degrees instead of the 68 degree thermostat setting. In my area we haven't even hit desgn day temps in the last 5 years.  

  • SWEISWEI Member Posts: 7,356
    good point about undersizing

    which is why carefully written contracts are important.  An informed customer can make a better decision, which is why we clearly state what the design conditions are and go over the difference a continuously circulated ODR system will make in their lives.

    If the 41k heat loss is accurate, a PTS60 is still 39% oversized for the load.  110k is just flat out wrong for it.
  • EdgemanEdgeman Member Posts: 15
    edited March 2013

    No one initially suggested the PTS60. Thanks for holding my hand throughout this analysis. I'm going to insist on the PTS60.
  • Charlie from wmassCharlie from wmass Member Posts: 3,922
    or you could go with a contractor that would size

    the boiler for what you need. How much of a hurry are you in to convert? Email me I service CT and MA.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • ChrisChris Member Posts: 3,056
    I Don't Think The Smart 40

    Is the right tank. I'd make sure I had the dump for those back to back to back morning showers. I totally agree on the boiler size choice. If you dump that tank the recovery is only going to be

    60,000 / 35,000 = 1.7gpm your sitting on the edge of a cold shower.

    The 40 gallon storage will give you a 26 minute dump. The 60 gallon 40 minutes til dump at the 1.5gpm you are telling us the shower head is.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • EdgemanEdgeman Member Posts: 15
    It is not a static capacity, it is a dynamic process...

    The Smart 40 indirect doesn't wait until all the hot water is used. It will start to recover after about 10 gallons or so. With 1.5 gal shower heads, I will be using less then 1.33 gallons a minute.

    But lets say someone is using a 1.33 GPM of hot water, and takes a 20 minute shower. So after 7 minutes of water use the indirect calls for regeneration/recovery. It recovers 18.2 gallons while the person is in the shower uses 17.3 gals in the last 13 minutes of the shower. Leaving 8.4 gallons that needs to be recovered after that shower is done. Which will take an additional 6 minutes. So unless someone hops in that shower as soon as the first person gets out of the shower. The second person will have plenty of hot water(40 gallons plus recovery gallons), and so will the third person.

    Or let say 2 people are showering at the same time for 15 minutes each. They use 2.66 GPM for 5 minutes = 13.3 gals. As recovery takes place, in the last 10 minutes they use 2.66 GPM while recovering 1.4 GPM or a net loss of 1.26 GPM x 10 = 12.6 gals, leaving 10 gals left. After the two end their 20 minute showers, the 3rd person steps into the shower under recovery mode using 1.33 gals while recovering 1.4 GPM. The 3rd person can take a shower as long as she wants as it is recovering faster than she is using it. It will take 18.57 minutes to recover after she is finished...

    Smart 40 which is actually 36 works.
This discussion has been closed.


It looks like you're new here. If you want to get involved, click one of these buttons!