I used HVAC_Calc.

[tobra]

I did a heat loss calculation using the HVAC-Calc from this site. I came up with Total heat loss 50,983 BTU. Would a 60,000 btu furnace be to small.I am looking at a Carrier 58mvc. 96% efficency.
60,000BTU at 96% = 57,000 btu
57,000BTU - 50,983 BTU = 6017 BTU 11%
Would putting in a 70,000 BTU 96% efficency be better?
House size is 1050sqft with basement. In Princeton B.C.


Thank you

[beenthere]

60,000 will work better.

[BaldLoonie]

Hope you have a big duct system!

I have a 60K 95% for a 1000 sq ft home. Well built so it only needs about 40K in the coldest weather. So really I can heat on low which is nice & quiet. But since my ducts were sized for a 65% furnace that moved so much less air, when it goes to high it sounds like I'm in a wind tunnel. Fortunately I can do without high, it's switched off most of the time. But I did buy an expensive single stage furnace.

[tobra]

That is also one of of my concerns, the larger the furnace the more cfm.
I know that the furnace is a Modulating and it has a variable speed motor, But I still should not go to much oversize, Right?

I had a installer come out, he walked into the house and said 80,000BTU. I told him I did a Heatloss Calc and came up with 50,000BTU. So I ask for a price on a 60,000BTU. He said that their is no way he would ever put 60,000BTU in.
The smallest he would go is 70,000BTU and I had to twist his arm.

The house is 37 years old, Main truck splits of furnace 8x16 both ways. The cold air return is 8X16.

[DanW13]

Since you have done the load calc on your home, now you should have someone run a manual D to size your duct work to match the furnace which by the way is a nice piece of equipment, make sure you get the Infinity controller along with the furnace.

[amd]

That's a lot of heat for 1000 sq ft. - draft proof and invest in more insulation if practical and economical.

[tobra]

I do have new low e windows and r38 in the attic basement is r12 walls.
The Hvac-Calc was pretty easy to use except for the part about outside design temp.
Temp in winter get to -13F -22F
Dipping to -31F
the coldest recorded is -45
so I used a design temp of -30F
Even if I enter the coldest day -45 I come up with 56800Btu

[amd]

Disregard my post - the design temp in most places is rarely lower than 0F. (I made an assumption)

[tobra]

I do have new low e windows and r38 in the attic basement is r12 walls.
The Hvac-Calc was pretty easy to use except for the part about outside design temp.
Temp in winter get to -13F -22F
Dipping to -31F
the coldest recorded is -45
so I used a design temp of -30F
Even if I enter the coldest day -45 I come up with 56800Btu

[beenthere]

If you had to twist his arm to get a price on a 70,000 BTU.
He's not a contractor you want to use.

[Junkers]

Using a design temp of -30 lets you know how much heat is required to maintain whatever indoor design temp you have entered. The question you can then think about is how many days a year would the temp go below -30 (and by how many degrees). You can then weigh the pros and cons of how much is it worth or cost during the rest of the year to have a furnace sized for the rare extreme worst conditions. If you want to include the extreme lows then you might think about a variable speed modulating or 2 stage furnace which might work more quietly with your existing ducts for most of the year.

Checking your duct airflow requirements is the next part as suggested, but r38 in the ceiling is not very much considering how cold it gets. See what happens to the heat requirements if you plug in r50 before purchasing a new system.

[tobra]

Using a design condition for Dawson Creek B.C. (Canada) which is in the far north. I come up with 52,484BTU. I am in Princeton B.C. south interior mountain. the winters are not as bad as Dawson Creek.
So design condition, -30F outside 72F inside=50983BTU
As far as how often it get below -30F ,may 4-5 time a year and this would be only at night.
Increasing R value in ceiling to R57 would give me 49,981BTU.
Will do this in 2-3 years.

[john_ertw]

The Canadian equivalant to Manual J is CSA F280. F280 allows for a furnace upto 40% larger than what you calculate using design conditions. F280 says the outdoor design temperature for Dawson Creek is -36*C (-32.8*F). Use -33F in hvac-calc to comeup with your heat loss. Then pick a furnace between what you calculate and 40% bigger (1.4 x calculated value). Keep in mind, your calc is only as accurate as the values you estimated for insulation, windows, etc.

PS. the summer design temp for Dawson Creek is 27*C.

[CardinalJoe]

......will tend to want to do their own load calc. Instead of using your own load calc, make sure you ask your contractor to do his own, and provide it to you before you sign on the dotted line. If he hesitates to do one, gives you the ;i've been doing this for ccc years and i know the size you need; line, you know to keep looking.

The other thing is that many companies will have you pegged as a high maintenance customer if you have already done your own load calc. Sadly, many just want to grab the money put in a unit that is too big, and get out of your house. You'll know when you have the right installer - he will tell you he is doing a load calc without you having to ask.

[tobra]

I used Dawson Creek only as a extreme. Because the HVAC-Calc Does not have Princeton B.C.. I live in Princeton B.C. and can not find anywhere what the outdoor design temp is.
Does anyone know what the outdoor design temp for Princeton B.C. is or how to figure it out.

[git-r-dun]

Check the average, high, low winter temps for that area on some online weather site. Maybe that'll give you what you need, or enough to safely assume a reasonable design temperature.

[john_ertw]

I used Dawson Creek only as a extreme. Because the HVAC-Calc Does not have Princeton B.C.. I live in Princeton B.C. and can not find anywhere what the outdoor design temp is.
Does anyone know what the outdoor design temp for Princeton B.C. is or how to figure it out.

According to CSA F280:

Outdoor design temperatures:
Heating: -27*C
Cooling: 32*C

Summer mean daily temperature range: 18*C
Outdoor humidity: 9.7 g/kg
Mean soil design temperature: 10*C

The advantage to using the Canadian standard for Canadian cities is it has the info needed and is focused on ensuring comfort in a Canadian climate, i.e., F280 is probably focused on heating more than cooling (ie, only sensible cooling loads are calculated and latent are estimated to be 30% of sensible loads). Manual J I imagine is more sophisticated for cooling although I have never read what the calcs encompass.

[Junkers]

HVAC-calc uses an oversize factor of 25% for heating to take care of those times when the temperature goes beyond the desgn extremes. It makes sense that CSA F280 uses 40% because of the colder winters. But in both cases that does not mean that you HAVE to use these factors to their fullest. For me I asked myself what winter temperature was the coldest that I remember AND whether or not I would want to size my system for that temperature or whether I could deal with that situation where the house was sized for a few degrees warmer. Then I put that temp (in my case -10F) into HVAC-calc and used that as my worst case design heat requirement and sized my furnace based on that. On the truly rare occasions that might go beyond that I can live with the house being a bit colder for what may amount to maybe two days every two years.

[tobra]

First I what to Thank You for helping me. I hope I am not being a pain. If I am I do apologize. The problem is that i live in a small town. The closes city is 75miles away and I am having a hard time finding someone to come out. I know time is money and I am willing to pay for time, but still no luck. I may have to use one of the local guys ( their are 2 but one I have hear horror stories about). The one guy I talked to was very nice with a good rep. and seemed like he knows what he is doing. But he is old school when it comes to sizing furnace.
I have redone my HVAC -CALC and added the right outside design temp for Princeton ( Thank You john_ertw). Also took a closer look at my windows and found I have Low-E (sticker inside window).
House is 37 years old, full basement, no overhangs, very little wind in winter.
I was hoping someone would look at it (files attached) and see if I missed something. I know the final decision is mine, and I will not hold anyone accountable. any advise would help.
I also listen to my old furnace last winter and I had no problem heating the house at-37F. It would run for 10-11 min then shut off for 4-5 mins. It is a 125000Btu 37years old.
Thank You

P.S. As far as getting a manual D done on the house I don't think it will happen. I am having a hard enough time with just the manual J (Csa-f280 in canada)

[beenthere]

Looks like you got everything.

[Junkers]

On the one hand. . . looking at your reports I believe you have used the simplified floorplan method for computing your house which is not as representative of your house. Using the simplified 4 walls and single window square footage number per wall there might some inaccuracy. . . but not a lot. The report you included used a winter design temp of -17 with a heat requirement of 39,726, but you earlier cited a heat load of 50,983 based on a design temp of -30°. The Carrier 58mvc output of 57,000 matches pretty well with that and leaves a bit of spare room for temps a few degrees lower than that.

On the other hand. . . The price difference between a 60 and an 80k BTU is not very significant considering in your location most contractors would typically inventory larger units, and with the variable speed modulation features that will help either one adjust to the temp extremes.

What I think about is the spread between the theoretical versus the actual. You had a 125k BTU unit of unknown efficiency and CFM operating at 66% duty cycle at -37°. Give the facts of the variable speed and modulating furnace and a BIG presumption that your existing ducts might handle the 80k unit's cfm you could go with the 80k unit and not pay a big price or performance penalty. Of course if the cfm assumption is wrong any your ducts for some reason are not sized right. . .that would be the risk of not having a manual D or review of the ductwork.

[tobra]

my first Calc was wrong. The proper design temp for Princeton is -17F not -30F that made a difference of 6500Btu. The Low-E windows made a difference of 3300Btu. And I changed from outside measurements to inside conditioned space, difference of 1400Btu.
The old furnace (125000Btu) is a little noisy, I can hear the air flowing. does anyone know what Cfm it would be, I'm guessing somewhere around 1200Cfm.
A 60,000 96% should be about 900Cfm 70,000Btu ( if I what to be real safe) about 1050Cfm. I know it all depends on my heat rise. But it should be less Cfm than what I have. I am not looking for the whisper quiet. My goal is to get a more efficient furnace that is a little quieter. Also this is a modulating furnace with variable speed , that should help. The only time it would run full Cfm is in the real cold and in the morning if I turn my stat down at night, this would be when the furnace may run full BTU output. . The rest of the time just maintaining temp if the burner is modulating at lower Btu output the fan will adjust the Cfm to what the furnace needs. IE: modulating at 50% 28,800BTU output ( not to cold outside) the furnace may only run 700CFM. Is this correct?
The duct that is in the house splits off the plenum 8 x16 one way and 8 x16 the other both are 11ft long. Cold air intake is 8 x16 with 3 /24 x 6 openings.
Again I am not looking for absolute perfection. Just something more efficient and a little quieter.
Thank You again for you help.

[DanW13]

The CFM on low fire or fan speed is roughly 424 CFM, on med Fire or med fan speed is should be roughly 800 CFM and high fire it is just about 1,040 CFM's

I have the 60K BTU 58mvc and from what I read on my stat is ran in low fire about 70% of the time thru out last winter maybe lower at about 60-65% at the lowest and I run the fan on low speed 24/7 Mid you the numbers for the CFM's are a rough estimate based on what I have read off my controller so as to give you a rough idea so do not take them as anything other.

[tobra]

I have managed to find a company that is willing to come out, will have to pay a small travelling fee but thats O.K. When I talked to them on the phone I asked about heat loss calc and they said that they alway do them and they also said they look at the ducts to make sure they are the right size. They also set the BTU output, heat rise. so things are looking up. I will see how they are when they come out and look. And how much they want.
I what to Thank everyone for their Help, I really appreciate it.

[AHH-COOL]

I have only one question. What's a furnace?

[jonpcar]

Tobra and others, thanks for the thread and posting the hvac calculations.

I have been considering puchasing HVAC Calc to do some what-if scenarios (insulation type things, etc) but have a couple questions.

When I had a quote for replacing one (of 3) of my systems, the contractor did calculations that included the orientation of the walls/windows and whether they were shaded or not, etc. My house is at a weird angle and actually faces SW, does HVAC calc take a wierd orientation into account?

Finally, does the low-cost homeowner version of the software allow me to run multiple scenarios (because I have 3 systems) with multiple options/changes? In other words, can I play with it as much as I want ? Or is it "crippled" somehow to limit the amount of scenarios that can be run?

Thanks.

[tobra]

I found the Hvac-Calc very easy. the only problem I had was getting the right Outside Design Temp, a member was able to give it to me. Having the right outside design temp is very important.
Yes it will do SW,NW,etc. also shading. As far as changes, I have had no problem changing numbers to run different scenarios. This I liked because I could see where to put my money to get the best return. For example if add more attic insulation or to put the money into sealing air leakage. I have been playing with it for the last couple days and have had no problems with it locking me out.
I do like the program and I feel it is well worth it, but as someone pointed out, the contractor my still what to do their own Heat-Loss calc. And they should.
If you do get it, spend a little time and watch the instruction video located in the table of contents.

[tobra]

O.K. Now I am really confused. I had someone give me price on a York 9C. He did a heat loss calc and came up with 91000BTU. so he want to put in a 100,000BTU furnace 98%.He says he uses a program from Wright . Can there be that much difference?
My old furnace is (37 years old) 125,000Btu at 60% effiency =75,000Btu. Am I wrong thinking that the old furnace is only putting out 75,000BTU.
This one is 100,000BTU 98%=98,0000BTU. That 23,000Btu bigger. I had no problem heating the house when the temp was -30F.

[sktn77a]

I'd ask what assumptions he made in coming up with 100,000BTU and compare these with the assumptions you made with HVAC Calc. Sounds like overkill, though.

[tobra]

He is 1 1/2 hours away so I gave him my measurement (I have recheck them 3 times now) over the phone. He said he used a design temp of-17F. So the 2 report should have been close. I ask how much of a safety factor he used and he said the program does that and that he did not know.

[beenthere]

Your old furnace is probably more then 75% efficient at steady state.

What did your load calc from HVAC Calc come up with.

[tobra]

The old furnace says 125,000BTU input and 100,000BTU output. So does that mean if this furnace running 24/7 would have a efficiency of 80%. 125,000 x 80%=100,000. Even if it is 37 years old? So when people say that the old furnaces are 50 -60% efficient they are only referring to the efficiency of the furnace for the full year (AFUE)?
I used -17F design temp, average air infiltration, average fireplace, ceiling R-38 ,Low-E =40,000BTU
I changed some things to the extreme. -17 temp, air infiltration farm house, fireplace bad, no low-E , ceiling R26 =57,000BTU
Even with these extremes at -50F (coldest in got 1968 -43F) =78,000BTU

[beenthere]

Correct. Steady state, it will still be 80%, or close to it.

But AFUE wise(the whole year), it may only be 60% give or take.