Massachusetts oil furnace replacement?
A coworker of my lives in a mid 1990’s built 2200SF colonial with attached garage and half finished basement in Groton, MA. A single furnace serves 2 floors and the basement, no zoning. They were just told the heat exchanger is cracked on their oil furnace. I don’t have all the details, but they have some sort of service contract and the tech noticed soot on the exterior of the power vent.
I’ve estimated the load at a design temp of 1F to be about 26.5kBTU/h prior to factoring in infiltration loads. A Mitsubishi 2.5 ton PVA with hyperheat would work or maybe a 3 ton Carrier Infinity Greenspeed. Ideal would be to split the ducting and do a Fujitsu 18RLFCD downstairs and a 12RLFCD upstairs.
Unfortunately they have no heat at the moment, two little kids, and short term budget constraints. It looks like a new oil furnace is what will happen. With that, improving comfort by choosing appropriate equipment seems the best option.
The current furnace is power vented. They have a proposal to do a 100Kbtu/h direct vent furnace and were told it could be nozzle down to 50Kbtu. I know nothing about oil equipment. What guidance do you all have on with regard to specifying and setting up an oil furnace?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Mitsubishi has ducted full size air handlers down to 12kBTU (SVZ-KP-NA).
We just installed 2 ducted air handlers on a MXZ-8C48NAHZ (along with 3rd zone as a ductless head) and they've been good thru the winter.
Get a second opinion on the cracked heat exchanger. I had a friend tell me her HVAC company said her furnace had a cracked heat exchanger and she should replace it, furnace was about 5 years old. I recommended my preferred HVAC (Marsh Heating) company do an inspection for her. They said her furnace was in fine condition. A lot of ripoff artists out there in HVAC, just like oil change companies.
Doug, I agree...cracked heat exchanger on a hot air system? The soot is probably from a mal adjusted burner or clogged nozzle or combustion chamber needs a good cleaning.
Residential hvac techs are being pushed to act like salesman now and tons of equipment is replaced unnecessarily. I know lots of people in the industry. Many techs are getting out of residential as they are somewhat being forced to be dishonest to hold their job. Companies make alot of money off installing new equipment and they push it hard. Its easy to convince a uneducated homeowner a fossil fuel fired unit is unsafe and they need a new one.
Oil furnaces usually have a 20 year warranty on them with some even offering lifetime warranties. How old was the furnace and what brand?
Most oil equipment is insanely oversized as well. I have been pretty much idling my 80k forced air furnace for 2 winters now. I self installed 3 12k cold climate mini splits and solar panels and the savings have been astronomical.
Classic dilemma, no gas, oil furnace to large, propane to expensive to run, heat pump price busts budget. What oil furnace can be down fired to 50kbtu? Is replacing the heat exchanger an option. It is possible with my furnace. Heat pump systems produce lower air temperature output so ducting my be to small.
I would stick with oil unless natural gas was an option. Then again, if budget is not an issue, heat pumps and solar panels.
It’s also worth noting that Groton is a municipal utility and likely has lower electric rates than the commercial utilities, so more reason to consider heat pumps.
http://www.grotonelectric.org/rates/tou-rates/
So I heard from the coworker that the furnace is getting replaced now. So this the focus is probably now on if there is anything that can be done to improve the situation in the short term like reducing output to get longer, more comfortable run times. I just know almost nothing about oil fired equipment.
Groton being on municipal power is a great location for heat pumps. There should really be more programs and equipment focused on direct furnace replace. Dropping the CFM to match the BTU output means that most existing ducting can work well.
Incentive programs should require fuel use history based sizing confirmation.
Fujistu should take their midstatic 1.5-2.5 ton ARU air handler and fold it in half to make an multposition 22"x23" air handler. The existing air handlers are almost 40" wide and no one is prepared to mate them to existing residential ducts. The modulation on those is much better on those than what I understand is offered by Mitsubishi air handlers with hyperheat.
Be careful thinking municipal electric utilities have lower rates, it's often, maybe even usually, the other way around. From the page you linked, Groton looks to have electric rates pretty close to the median pricing for the US (about 10-15 cents per kWh with everything included). Those aren't bad rates, but aren't great either. I'd call those pretty fair rates. The municipal electric companies don't have the same incentives to try to be efficient in their operations that the commercial companies do, which often means higher they charge higher rates for the same services.
For the OP, I'd get a second opinion on that heat exchanger. I work with commercial HVAC companies a lot at work, and I had one of my favorites do some work at my house. Since they don't do much residential work (only "family and friends" as they put it), the owner of the company asked his York rep what a normal residential price would be. Shortly after that I got a call saying how he was "in the wrong business, residential companies rip you off like you wouldn't @#%!@% believe", or something along those lines. I got the stuff at their cost (perks of awarding big contracts to them :-), but there is a lesson there... If you're looking at getting any major residential HVAC work done, BID IT OUT.
Bill
Massachusetts has like the 3rd highest electric rates around .22+kwh so thats cheap compared to the rest of the state.
The municipal electric utilities in Mass also have a really generous $1.20 watt incentive for solar. I believe its is good up to a 4kw system so you would get $4800 back. I would be all over that if I lived there. I did the math and a 4kw system would cost like $3200 after the tax credit and incentives there.
https://www.mass.gov/guides/municipal-light-plant-solar-rebate-program
Bill, a second opinion would have been good, but this isn't my house, and upset partners and concerns of kids in cold bedrooms work strongly in favor of the status quo until we do things to make the transition to modern heating systems easier.
Here in Mass we are in the land of high electric rates as BFW references and high gas ($1.40/therm). Break even for a ASHP with HSPF of 10 vs a 95% gas furnace (14.74 $/mmBTU) is around $0.15/kwh. Oil runs around $24-25/mmBTU, so break even is anything sub $0.24/kwh. I knew oil was expensive, but I didn't understand how much so until just running the numbers, bummer.
Solar makes a lot of sense at $.24/kwh. I am currently at sub $.12/kwh on another municipality with a time of use plan. This which pushes even incentive assisted solar closer around an 8 year break even last time I looked. That is not the worst, but I have other lower hanging fruit to tackle first. It might be less time if when factoring in time of use ($.108/kwh off peak, $.172 peak 12-7pm).
Bill:
Not sure if you're familiar with the marketplace in MA. It sounds like you may not. The northeast US has some of the highest electricity rates in the country (other than CA).
Last I checked the commercial utilities in Boston were getting above $0.20/kWh.
Groton's Peak TOU rate with prompt payment discount is $0.1356/kWh. Off peak is an amazing $0.0855/kWh.
We're in a different town with a muni utility. On our TOU rate with solar, we pay about $0.11/kWh in the winter.
I was thinking in terms of comparison to the national prices, not so much local. I work with VERY heavy electrical users in my industry, and a primary concern for siting new facilities is usually electric rates. And climate, since air conditioning is cheaper in cooler locations. I don't see many new datacenter projects going in in the Northeast, but there have been many in the pacific northwest (one of the cheapest areas for electric power).
Note that anyone using a "time of day" electric rate will find that solar is a nice fit for the peak times, which is usually the late morning through early evening. Much of that peak time will line up with your peak solar production, so you can save even more on that type of electric rate if you are also running solar!
Bill
Conrad B
As an oil burner technician, down sizing the direct vent 100kbtu/hr furnace to 50kbtu/hr is absolutely wrong, voids any warranties and is dangerous. At a minimum, you risk the creation of condensate forming in either the heat exchanger or the chimney for which the equipment is not designed (high corrosion risk). Every oil-fired appliance comes with minimum and maximum btu ratings/ nozzle sizes, and they need to be respected to ensure no condensate forms, and that proper venting, especially atmospheric venting with chimneys function correctly (i.e. flue gas temperatures to low will affect operation of the appliance). Hence, don't mess around with the safety factors built into an appliance and select the appropriate equipment for the job to be undertaken (e.g. perform heat loss calculation and select the appropriate equipment). People have died from carbon monoxide poisoning from damaged heat exchangers and failed chimneys.
So is reducing output of an oil furnace even thing?
For gas I know it is it is not unless you go rogue.
Hi Matt,
Whereas gas furnaces are built and sold with a specific output (aside from stages and modulation), oil furnaces fire at only one rate typically controlled by the oil pressure and nozzle size. So for gas furnaces you would select a model to meet your specified heating requirements (e.g. a model rated at 75Kbtu/hr). But if you were purchasing an oil-burning furnace, you would commonly find that one model might be rated from 60-85kbtu/hr, and the installer would select the pressure and nozzle size to match the 75kbtu design capacity. What you will notice is that the model's selected range of capacity is limited, and never anywhere near 50% of its maximum range.
Also, when an oil technician comes across an unfamiliar older piece of equipment without rating information, in an effort to reduce cycling and improve its efficiency, they may reduce the capacity or nozzle size by about 10% as long as they are still getting good combustion values (e.g. oxygen/carbon dioxide values, temperature) after any adjustments.
So we lost this battle, the new oil furnace is installed and running. Word is there was soot coming through the supplies. I don't know if you can tell the difference between soot and dust. Suspiciously, the old furnace was gone when he requested to see it. CO alarms powered and never went off.
They are interested in the idea of doing a ducted minisplit to take over heating and cooling the upstairs, which would be a significant comfort improvement. The layout seems workable with 80% of the ducting in conditioned space.
Generally soot when rubbed smears and does not come off readily with water whereas dust does not smear anywhere near as easily and tends to come off surfaces quite easily with just a damp rag. Soot will often also smell of heating oil, not a burnt/smokey smell from burnt dust. Unlike dust, soot can very easily be drawn to vertical and overhanging surfaces (walls and ceilings).
Keep in mind that soot can come from other furnace components besides the heat exchanger. Any place where combustion gases can leak out into the building (or even back in in some cases) are sources. Examples include flue/chimney connections, burner to appliance seal, barometric damper, viewing port and the test port(s).
>"They are interested in the idea of doing a ducted minisplit to take over heating and cooling the upstairs, which would be a significant comfort improvement. The layout seems workable with 80% of the ducting in conditioned space."
I'm confused. They are interested in mothballing/retiring the BRAND NEW oil burner?
Or, are they thinking about breaking it up into zones, with a ducted mini-split on the upstairs, the fossil burner doing the rest of the house?
If breaking it up into zones...
With the oversized air handler of a 100K oil burner the ducts might be already big enough for a right-sized low-static SUZ/SEZ ... NAHZ (cold climate version) solution. Even the 3/4 tonner puts out 12,500 BTU/hr @ +5F, and they come as big as 1.5 tons, good for 21,600 BTU/hr @ +5F:
http://meus1.mylinkdrive.com/files/M_SUBMITTAL_SEZ-KD09NA4_SUZ-KA09NAHZ-en.pdf
http://meus1.mylinkdrive.com/files/M_SUBMITTAL_SEZ-KD18NA4_SUZ-KA18NAHZ-en.pdf
At -13F they'll still put out more than 75% of the AHRI rating. I suspect even the lossiest single floor would have heating & cooling loads within range of the 1.25 or 1.5 tonners that series.
A right sized mid-static Fujitsu would require less duct analysis and can be had in up to 4 tons if need be.
You can probably find the relevant local contractors near Groton (and compare average syste pricing among them) on this Mass CEC page:
https://www.masscec.com/cost-residential-air-source-heat-pumps
Zoned was the thought. It would be a couple years out for them. The master bedroom has a cathedral ceiling so dropping the height a bit to create a soffit within the conditioned space would work well Everything could run off a few short duct runs and central return.
The impact on shutting off a bunch of ducts from the the oil furnace would need to be tested prior to going forward with splitting things.
A 1 ton upstairs and 1.5 ton downstairs is likely the ideal solution from a comfort standpoint, but is full on retrofit project.
A single 2.5 ton serving the whole house would have still been a significant comfort upgrade. It is going to take awhile before installers are quick to drop in ASHPs in emergency replacement scenarios.