My house is almost45 years old - only 2X4 framed, brick veneer and aluminum siding with double glazed Low E argon filled vinyl windows and about 2 feet of loose fill fiberglass in the attic. The basement is insulated to about R12 - almost as good as the outside walls. We spend about $700 a year on natural gas which operates the furnace and the water heater. Changing from the original 35 year old furnace to an 85%+ 2 stage
35/50 TempStar with variable speed DC fan didn't reduce our gas bill at all.
If your new unit is only 85% eficient im not suprised, most old units are 80-82% efficient, going to 95% plus would help, but your gas bill is still minimal for yearly cost. Ive done about the same as you in insulating.
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40000 input and its likely 38000 output, 3 burners on my stove put out more than 38000 btu, my whole stove-oven might put out 60,000 btus, He cant have any recovery with 38000 btu. I say its undersized and not up to modern insulating standards or what you have. But if no load calculation was done everyone here is just guessing, and maybe his installer guessed also, from the old boiler size, which is different than forced air.
If your new unit is only 85% eficient im not suprised, most old units are 80-82% efficient, going to 95% plus would help, but your gas bill is still minimal for yearly cost. Ive done about the same as you in insulating.
You guys are all missing the point (I think) He is complaining about vent output temperature. Even with 100,000 BTU, if the fan runs too fast the outlet air temp will be too low.
He has to start with making sure the temperature rize across the heat exchanger is correct. If it is not, the blower speed needs to be adjusted and/or the ducting corrected to provide proper flow and heat gain. IF with the correct heat rize the air flow is not enough to heat the house, the furnace is not putting out enough heat (btus) either because there is something else wrong, or the furnace is too small.
If he is getting high enough temperature at one duct, but not at another, he has a duct ballancing issue and the installing contractor needs to correct that.
According to a study I saw when looking to replace my furnace, the vast majority of furnaces in North America are oversized for the application, and suffer in efficiency because of that. I'm looking for the numbers, but CMHC (Canada Mortgage and Housing Commission) states "the majority" of homes in canada have oversized furnaces. The "consumerresearch.com" states "A recent New Jersey study shows that most furnaces are significantly oversized"
From
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A recent study has shown that the average furnace installed in a new home in Anchorage, Alaska is oversized by 121%. The study was conducted by Phil Kaluza, a researcher with Arctic Energy Systems, and was sponsored by the Cold Climate Housing Research Center through a grant from Alaska Housing Finance Corporation....
The ALASKAN report indicates a "rule of thumb" 19 BTU per sq foot is on the high side. Boston would surely be significantly lower.
It is considered a high efficiency non condensing furnace. The furnace that came out was "rated" at 75%, and the last time I had it tuned the tech checked it and said he thought he had made a mistake, so checked it again, and it was over 80%.
The ECM fan is so much more efficient than the old belt drive induction motor fan that the furnace needs to be more efficient just to maintain the same consumption.
The ECM fan draws 400 watts less on low speed, on average - producing a BTU deficit of about 1300 btu/hour just for the constant run consumption.
When running at high speed (heating) the ECM blower saves roughly
400KwH of electricity - requireing between 11 and 29 cu meters per year more gas to make up for the BTU deficit (approx 1,365,200 BTU) according to a Natural Resources Canada study (Google canmetenergy ecm effects)
Of course you are not saving any cash, you might have taken out a good 82-85% furnace An 85% furnace is not High Efficency, your manufacturer called it so as a sales gimmic. H.E. is a condensing unit
93-98% efficient, thats no marketing gimmic. 82-83% efficient heat has been available for maybe 70 years and more than 100 on boilers. 82% units are just not sold by law anymore. I have a 1955 1,300,000 btu Kewanee thats 83% efficiect steady state, continous running.
A contractor Can Not rate a systems efficency to the standard AFUE test in your home, it requires a test facility with near $50,000 in test equipment that is Gov certified and maintained, he can only test Combustion Efficency. And there he lied to you to sell you a new unit because to get 85 % combustion efficency you would hardly be burning the gas, or an oil burner would be all smoke. Its impossible for him to do the tests to Rate a systems overall efficency. He lied to you again.
Even if OPs blower is set to high he still would get the same Btus, but he still has no recovery in his temp rise number, realise he might be getting 37-39000 btus, just 3 burners on my stove-oven are 38000 and I could not heat my house with 3 burners on my stove stove or with the oven running giving more Btus, its just not enough Btus. 38000 might work on a super insulated house, one built to high Canadian standards, standards we dont have inplace in the US yet, some houses are built to them, not many not enough.
I'm sure some/many people will correct me, but here's what I'd do.
Spend some quality time with the gas meter and a stopwatch. Verify that the gas going in is correct for the BTU rating of the furnace.
Log the percentage of time the gas is on in the steady state. In my case, it's 1.5 minutes less than the fan runs each cycle. Measure the difference between inside and outside temperatures.
Calculate the inside-outside temperature difference on the coldest day of the year.
Ratio this calculated future difference to the current measured difference and multiply by the percentage on time. If that is > 100%, you've got a problem. Yes, there are issues with wind, snow, SHG, etc, but you gotta start somewhere.
On a day with no wind, open one window a crack. Open all the interior doors. Turn on the furnace fan. Take a burning incense stick smoke generator to the window. A lot of air moving in or out suggests that you have a leak in the system somewhere.
You can do a similar test by turning on all the exhaust fans in the kitchen/bathrooms and use the smoke stick to look for air coming in the registers.
This assumes you don't have a fireplace...or you need to account for that major hole in the system.
I just replaced a 120,000 btu 70% furnace with a 60,000 btu 95.5% furnace. Air coming out of the registers went from 140F to 105F. And that's higher than it should be. Doesn't help that I have the registers closed in half the house, so the effective duct size is too small.
You have at least two issues.
1)heat loss thru insulation/infiltration.
2)thermal mass.
With excellent insulation, it takes little heat input to maintain the temperature. But if you CHANGE the temperature, it can take a lot more heat because of the thermal mass of the system.
After a major insulation upgrade, I started to notice a phase shift in the cooling load. The air conditioner worked harder around sundown than it did during the hottest part of the day. Fortunately, I can open the windows at night, so it's a good thing. Near as I can determine it's because of the increased thermal resistance coupled with the increased thermal mass of the insulation and the air trapped within.
But the total BTUs of heat the furnace is putting out is going into the living space, whether the heat rise is 20 deg with a fast blower, or 40 deg with a slow one. So, it should not make a difference in whether it can raise the house temp a reasonable amount in a given time. The only exception I see would be if the fan speed were so slow that the temp got too high and it caused the furnace to stop firing.
I took out a 35 - or I guess 38 year old furnace so I'd be replacing it on my terms, instead of it's terms. It was a relatively cheap contractor grade furnace, and mine was one of the last 2 on the street still in operation. I was involved with the addition being installed on the neighbour's house, which required replacement of theirs - the other one still in service - so I negotiated replacing both at the same time. I think I got a good deal.
You have your definition. I have mine. It is a high efficiency non-condensing furnace. What makes it high efficiency? It has forced draft burner, not atmospheric burner, and it is a two stage furnace - with a variable speed electronically commutated DC blower motor.
7 years ago, or whenever it was we replaced the furnace, this was allowed to be sold as a "high efficiency non condensing furnace" and is every bit as efficient, over-all, as a single stage condensing furnace with an AC multi-speed blower. (counting combination of electrical efficiency and gas efficiency together)
He didn't lie to me to sell me a furnace. It was 5 years later that I had it replaced, and not by him or his company. He was surprised at how high the efficiency of the furnace was - and he measured inlet temp, outlet temp, stack temp and something else I can't remember to come up with his "efficiency" number. He said he had not seen one of that type of furnace running as efficiently as mine was - and he didn't make a single adjustment to it.
I didn't see the OP complaining about recovery - only the fact that the air from the heat outlets was much coller than what he had before
- and then at the same time he said it was replacing a boiler - so I really don't know WHAT he was complaining about.
The fact that one was 85 degrees and the other only 70 something, from what I remember, is what makes me believe it is not JUST a furnace size issue, if it is a furnace size issue at all.
OK, since you agreed with the first part - are you dissagreeing with the final analasys, or just adding an observation?
Is there ANY other option, given the first conditions are met, than the furnace being defective (something else wrong) or too small??
The main complaint the guy had was not that the furnace could not heat the house. He FEARED it might not be able to heat the house because the outlet air temperature was lower than he expected (rightly or wrongly)
Except the OP clearly stated that his home USED to be heated by hot water baseboard heat rather than the *NEW* forced hot air system... Therefore he has NO basis for comparison since he never had heat duct registers before...
Now, your point of duct size, duct balancing and duct insulation would make the problem of having an undersized burner EVEN worse than the suggestion that the houses insulation and windows were not properly accounted for in the heat loss calculations made prior to selecting the SIZE of the unit that was installed...
The fan speed setting at which the air in the ducts is circulated can not compensate in any way for an undersized burner...
This is an example of why field conditions in a home MUST be examined prior to doing ANY sort of work on the building...
The OP pointed out that the heating system was replaced because persons unknown stole the copper piping from the baseboard system... Well, I highly doubt that any analysis of the overall status of the building envelope was done by the heating contractor he called in to replace the scavenged heating system -- he would have better spent his money replacing the cut out copper piping than he seems to be with his idea of replacing the whole system with something new because he selected an unqualified professional who lacked the proper assessment skills to properly determine what size heating plant to install in the home...
While you have brought up some interesting issues which could explain SOME of the problem, you are not adding up everything that has been stated by the OP to see that while the concerns you address may bear some fruit, they can not add up to the entire heating gap the OP is experiencing from his clearly undersized heating plant based on his total lack of knowledge of the status of the insulation rating sealed up in his walls, or the energy rating of his window and door openings...
The shell of the building and the insulation values involved are of primary concern when doing heat loss calculations to figure out the maximum heating load that the heating plant must be able to accommodate on the "coldest day of the heating season"... Honestly it is better to have a system that is rated at 1/3 more btu's than you need than to have one that is just barely enough to heat a home which complies with the most ideal insulation conditions and would otherwise be clearly undersized because someone assumed an insulation value was inside your walls that doesn't exist...
The OP at this point in time needs to have a more qualified and experienced heating contractor come out and evaluate the overall condition of his home... He might be looking at either replacing the new heating plant with a larger one which can support the ACTUAL heating load present, or spending SERIOUS money replacing all the windows and doors and upgrading the R-value of the insulation...
Poor installation techniques on the duct work would only make the issue of an undersized heating plant worse...
There is no excuse for newly installed duct work to not be 100% covered in foil faced R-9 insulation batting which is sealed at every seam with foil tape... And that insulation is applied ONLY after the ducts have been either foil taped or gotten a coating of mastic at every joint or seam...
Since this duct work is BRAND NEW, it SHOULD NOT be a factor in the "my house is too cold and the furnace can't keep up" complaint since the duct work was supposedly installed by a competent HVAC professional... Agree ?
The OP's problem seems to stem around insufficient thermal mass and a system without enough heating capacity to properly heat the space given the overall condition of the house...
All true, but it could be as simple as insuficent gas supply, and im sure a test with a manometer was never done yet. He does need a real Pro to come in and re evaluate everything.
One fact, you dont even know what you have, and you need to start there. I just looked a Grandaire furnaces site and they dont make a
40k Btu input or output rated unit in 80 or 90%. They have in 80%
43/36 and 54/45. In 90% 55/35, and 60/38. So f you have the smallest
90% you get 35000 Btu, if its the 80% you get 36000 btu. Not very much at all, Two burners on my stove do 35000 BTUs !!!
You can check temp rise to see if its firing 100% or getting 100% needed supply, [ still a manometer test is needed ] Place a probe thermometer at the furnace intake and one just at the top of the unit [ you have to drill a hole so if you have AC dont do this unless you are sure of where the AC coil and lines are ] the difference of the two is a rise of only 30-60f for the 90% unit.
Bottom line, pay an experianced top line pro to figure it all out, your buddy is a hack. Did this guy get a permit or is he even lisenced, I bet not and that might help you to get him to fix it free after you figure out the truth. If he is at fault you could pull a permit now saying you thought he did it, the inspector will make him fix it. Ive done it.
One thing not mentioned is the calculations. The size is on the bottom end, but in a well insulated house, it is very adequate. OTOH, in a poorly or non-insulated house, it is very undersized. We just don't know enough.
Poor reasoning for your conclusion, though you may be correct. He is in the Boston area and hot water heat is still installed in brand new houses that are well insulated. Many are oil fired as natural gas can be difficult to get to your house in New England. The fact that the heating system had to be replace leads me to believe the house is likely 25 years or older. That was the time period that insulation was being used better because of the
70's oil crisis when everyone wore a Jimmy Carter sweater.
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