Oil to Gas conversion - doing the math!

balmyinboston

Hi all,



I'm currently looking into changing my heating system from oil to gas but need some help understanding how much I should expect to save.



The current heating system is a Weil Mclain 468 which I believe is from 1997 (see images attached). The house is a 1400sq ft single family home with 3 heating zones + storage tank. The heating zones are forced hot water baseboards which consist of a finished basement room (100sq ft), 1st floor (700sq ft) and 2nd floor (600sq ft) approx.

 

I'm located in the Boston area so I'm looking to get the switch to gas done before the 0 degree weather that is not too far away. However I'm not fully convinced on how much $$ I will save per year from the conversion....



What I currently spend on Oil: I bought the house in 2011 so just have one year to reference from. Last winter was not cold, however over the course of the year I spent about $2200 on oil. This was with no heating running from May to October, and in the colder months when it was running the thermostat was set to 60 during the day and 68 in the evening. The hot water use was 2 to 3 showers a day on average and a few diswasher and washing machine runs per week...



Cost of Conversion: I've been quoted around $9k (after rebates) for 2 types of conversion: A burnham ES2 (85% eff) with 40gal superstore and outdoor reset or a Burnham Alpine (96% eff) also with the same superstore. I received multiple quotes and they're all coming in around the same amount. One installer was keen to use the ES2 as he saw it as a good fit for the baseboard system I have.



I had a Mass Save Energy assessment carried out. My house has good windows and ceiling insulation, however it lacks insulation in the outside wall. The assessment concluded that my two main energy savings would be from adding pump-in insulation to the outside walls and the oil to gas conversion. By carrying out each improvement alone it was calculated to save me $800. They did not give an amount saved by carrying out both improvements.



Obviously the insulation is a no-brainer since there are rebates on the insulation and it would cost $2.5k after this, repaying itself in about 3 years. However at $9k the gas conversion would take years to recoup going by this calculation...



I have a number of questions that I was wondering if anyone could help me with:

1) Would the gas conversion provide more savings than $800 a year that the assessment stated, given the losses in my current setup?? There seems to be a lot of standby losses keeping the storage tank at temperature? Would there be a considerable improvement in efficiency even with the 85% efficient system?

2) If I chose to keep my current system and keep it maintained, will this cost me more in the long run, say over 10 years? (the length of time I plan to keep the house)...



Thanks in advance.

nicholas bonham-carter

Costs of going to gas

We don't talk about money on this site, as the costs of installation are not those of a commodity which could be the same from Oregon to Massachusetts.

The biggest benefit of making the switch to gas will be in having the needed fuel arrive without preordering a set minimum amount. The downside is being tied to one supplier.

If you are looking for economy then make sure your system is well maintained.--NBC

Aaron_in_Maine

Old

That boiler looks more like 87 rather than 97. I would change it out while I was getting a rebate. Rather than waiting and not getting a rebate when the time does come.

BobC

Superstor is a big chunk of that quote

How many people in the house? The superstore is great for heavy users of hot water but could be 25% or more of that quote - the tanks and pumps are not cheap. I'm changing over to gas in the next week or so and have elected to stay with my gas hot water heater because i just don't use a lot of hot water.



Blasphemous as it may sound, have you looked into the new heat pump hot water heaters? I've seen some great rebates offered on them and I know a couple of people who have them and have seen great cost reductions on their electric bills. You could always  go the superstor route if your hot water needs increase in the future.



Bob

Zman

Neither!!

First things first.Has anyone checked the boiler sizing? Do not assume the one you have is correct.

I really do not understand Burnham calling an atmospheric single stage boiler "high efficiency". Unless you have a single zone system that is matched perfectly to the load, you are going to have excessive cycling.It is kind off like like driving to work and  going a hundred miles an hour for a couple minutes then pulling over for a couple.



The alpine option will provide good turn down ratios and efficiency. It is built on an obsolete heat exchanger design. I would do a mod con with a "firetube" heat exchanger.





Here is a spreadsheet for calculating you savings www.eia.gov/neic/experts/heatcalc.xls



Your existing boiler is probably running in the low 70% range. A single stage burnam will never run at 84% in a zoned system, I would do high 70's. The modcon will run around 88% in your installation. Plug in you local rates and you will have your answer.



Opinions will vary on this one,

Carl

Jason_13

Opinions

Some info is opinions and some is fact. The fact is that a mod/con takes a much bigger hit on efficiency as water temperature climbs. The second fact is cast iron has a much higher thermal transfer than stainless steel. The third fact is most of your efficiency is set by the system not the boiler and proper sizing. The cast iron boiler will have a higher standby loss but kept at a minimum due to sidewall venting, ODR and proper sizing.

Opinions;

If it takes 20,000 btu's to heat a home in a given hour it is 20,000 btu's. If the boiler runs at a minimum input or three to four cycles to get to 20k we get to the same place. If both products are sidewall vented, properly sized and same layout how much different is the operation costs? With the cast iron which has more thermal mass the transfer of heat will be much different than the mod con. With the mod/con and reduced input but the same flow all the time you will be working with slower increase in water temp which is not a bad thing. The cast iron will increase the water temperature bit faster which means more heat from the baseboard. Both unit will satisfy the thermostat at different rates.

The link above is not accurate as it does not address modulation. I believe the true difference with all being equal is less than 5% on fuel use.

Zman

See what I mean.

Jason,



It is fairly common knowledge that boilers,any boilers do not achieve design efficient until they are running at "steady state". This is clearly explained in "Modern Hydronic Heating" by John Seigenthaler. The next time you have you analyzer in flue, check it out.



If you take 2 identical boilers and you set up one to run for 20 minute on and 20 minute off cycles and the other to run 2 minutes on and 2 minutes off. The first boiler will be much more energy efficient (and last longer).



Mass does help buffer the cycles.



The DOE  link is "dead nuts accurate". It is called science. garbage in, garbage out.



Mod/con boilers are 88% efficient when not condensing.



Here are some impartial tests.

 http://www.pugetsoundashrae.org/PDF_files/TEGALanders.pdf



Here is an explanation of the differences between mod/con and single stage boilers.

www.pugetsoundashrae.org/PDF.../AshraeCondensingtechnology.ppt





I have yet to do a Mod/con upgrade that did not yield at least a 20% reduction in fuel bills.



These are all facts.



Carl

balmyinboston

Some additional Info

Hi guys thanks for all your input so far its been giving me a better picture of things.



BobC: There are 2 sometimes 3 people in the house, so you can assume at least 2 or 3 showers per day. A few dishwasher runs per week and a few hot washes from the washing machine. With my current system of oil + 40 gal booster tank, I have never run out of water. Would consider heat pump hot water heater a better option than say a tankless modcon system? I had considered the Navien combi.



Zman and Jason: The boiler models recommended by two separate plumbers have had a size of 105k (actually two of them independently recommended the ES2). One of the plumbers went to great length recommending the ES2 over the Alpine (even though he installs both) for my setup, citing the return temperature as too high for the Alpine to work at max efficiency. The ES2 he stated on the other hand wouldn't have this problem and could work at close to the same efficiency with an ODR. The main benefit of the ES2 was a proven reliability with the combustion chamber and less maintenance costs overall. I guess your discussion raises a few questions to this theory:



Why would the ES2 be working only in high 70s efficiency for a zone system?



How can a modcon be setup to work efficiently with a high return temperature? I was simply told that it couldn't handle the return temperature at all and would work so hard to find a good operating point that it would no longer be efficient??



Thanks.

CMadatMe

Remember

Your looking for the payback on the added investment of a mod con vs another system not the total cost of the mod con installation. If it cost 100 bucks to install the conventional system and 300 bucks for the mod con system what is the payback on the 200 bucks not the full 300..

Zman

Cycle length

The alpine will achieve right around 88% when it it not condensing. You can likely set your ORD so that it will condense on warmer days.It is designed to run at higher temps as well, this is not a problem.

The ES2 is rated at 85%. I don't think anyone will ever see this efficiency. All these tests are in a lab using cold return temps. In an install were no short cycling occurs, I would expect low 80's. With extreme short cycling, I would expect low 70's. These are my opinions based on the facts presented in the ashrea document I previously posted.



If you know the number of feet of baseboard in each zone, the rough amount of piping you have and the widest on off boiler differential the boiler can be set for, I can give you an idea what you cycle length will be.



By the looks of it you will short cycle.

Why such a big boiler?



As I stated earlier, I would not install either in my own home (opinion)



Carl

BobC

Electric HWH tank instead of Superstor

The two instances i know of have couples using a 50 gallon model of the heat pump water heater and are happy with it.



There is also the option of using an electric hot water heater (electric elements NOT used) tank in place of a Superstor with the electric hot water heater thermostat being used to control the boiler and pump for the hot water function. One of the guys on the board posted details a couple of years back and it looked very workable, If I can find the post I'll post the link for it.



Bob

SWEI

Do this right

Begin at the beginning - what is your estimated heat loss now?  What is the estimated heat loss after the walls are insulated?  For a climate like Boston, insulation is almost certainly going to give you the highest ROI and should be done either before or along with the boiler replacement.  It's the "gift that keeps on giving" and will keep paying back year after year over the entire life of the structure.  It will also reduce your cooling load in the summer, so if it's at all affordable, just do it.



Carl has this spot on and you should heed his advice.  A properly installed mod/con will save significant amounts of fuel.  I also prefer (strongly) fire tube HX designs and would recommend you ask your contractor to install a properly sized "smart" circulator with the boiler.

Paul48

time

I ran the numbers about 6 months ago, and gas was 50% cheaper per therm than oil, here in So. CT. I'm having an ez-gas installed next week.

balmyinboston

so here's the numbers

thanks all for the feedback.



Zman: Re the boiler size - I don't know, this same size was recommended by two independent plumbers.



Ok so here's a rough measurement of my zones:

Zone 1 Basement (1 room): 12ft of baseboard

Zone 2 Floor1 (kitchen/mudroom/dining/living room): 72 ft of baseboard

Zone 3 Upstairs (bathroom, 3 bedrooms): 70ft of baseboard

Hot water zone: 40 Gal tank



Does it make more (or less !) sense why they picked those boiler sizes? Will short cycling occur?



SWEI: I had the mass save assessment carried out - they gave all energy use in $ amounts.

Conditioned Area: 1,446 sq ft

Conditioned Volume: 11,134 cu ft

Annual oil cost breakdown: Heating 85% Water Heating 15%



Current Annual  heating cost: $1950

Savings of pumping insulation into outside walls (its in ceiling already): $847

Savings of  converting to Gas Hyrdonic Boiler 90% AFUE: $781

They didn't give a savings figure for carrying out BOTH improvements together...



I'm currently working on getting the insulation done. I realize this will pay back much sooner than the oil to gas conversion. I'm still interested in whether converting to gas is feasible for my situation.

Mark N

Oil to Gas

How much does a therm of gas cost where you live? How much is a gallon of oil? Multiply the price of the gas by 1.4 and compare it to the price of oil. That will tell how much you save just in the difference in the price of the fuel. Where I live the price of oil is 2.5 times the price of gas. That makes the decision very easy.

CMadatMe

Heat Loss

If your heat loss is 40,000 btu/hr you'd be lucky. You have enough board existing that could deliver 86,000 btu/hr using 180 degree water. If the mod/con and system are designed, installed and set up properly you could see 50% savings.

balmyinboston

So in summary...

Thanks Chris and others. So after all the over and back this is the summary of my dilemma, my options are:



(a) continue with Oil heating (70% efficient):

Advantages: No upfront cost

Disadvantages: spend the extra $500-1000 per year on combination of expensive fuel and poor efficiency system.



(b) convert to Burnham ES2 Atmospheric boiler (80-85% efficient)

Advantages: Proven reliable boiler, simple to fix, low maintenance. Improved efficiency over oil.

Distadvantages: Upfront cost $9k; possibility it will short cycle. Not as efficient as Mod/Con system



(b) convert to Burnham Alpine or similar Mod/Con system (85-95% efficient)

Advantages: Highest efficiency

Disadvantages: Upfront cost $9k. Unproven long term reliability (will it last 10/15 years?), concerns it won't work well with baseboard heating

 







Is there anything I'm missing here? 

PMJ

Easy Decision

I just looked into the shocking bills on a Cape Cod home kept at 50 degrees over the winter wondering why they were so much higher than for a much larger home in Cleveland heated to 70. What I found was that currently the cost of natural gas heat and oil heat aren't close. Oil has a heating value of about 140,000btu/gallon and that gallon is currently costing at least $4.00. Natural gas(at least in Cleveland) currently costs about $4.50/1000 cuft delivered which is about 1,000,000 BTU. So, $1 of oil buys about 35,000btu while $1 of gas buys 222,000 btu. The same dollar buys 6.3 times more heat in natural gas.

This checks out because the 1926 Cleveland home had no insulation, was 3 times as big, and had 1/2 the heat bill of the Cape home.

Unless the gas cost in Boston is way higher than Cleveland there is no decision to be made here.

 

SWEI

you're overly pessimistic on the mod/con

A conventional atmospheric boiler WILL short cycle on this system unless you add a buffer tank.  For maximum comfort, you should also add a motorized mixing valve with an outdoor reset control.



Mod/con system will run at 88-98% efficiency depending on the operating temp.  Given that your baseboard is sized @86k, if your design load really is under 50k, you might end up at 92-94% for the season.  Standby losses plus short cycling will put the 82% boiler down in the 70-something range for the season.  I can't speak to the Alpine, but there are several mod/con boilers with track records that make me comfortable saying they should be good for at least 15 years with proper installation and maintenance.  There may also be rebates and/or tax credits you can take advantage of with the mod/con.  Have you looked at a Triangle Tube PT60 or a Lochinvar WHN-055?  Either of those would be a great fit with your load, and would not require primary/secondary piping (two pumps) for the heating system.

Zman

Not all Mod/cons are"similar"

The old generation of mod/con were high maintenance. The burnham alpine has the same Giovanni exchanger as the the munchkin and several other dated models. The firetube exchanger in the Lochinvar and Triangle tube models is very different. I have had one for 5 years and have spent no money on repairs. It is simply not fair to put them in the same category There are no disadvantages. Of course it will work with baseboard heat.

Carl