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Do my own heat loss calculation?

vilord Member Posts: 48
edited January 2019 in THE MAIN WALL
I've been (for the last two years) trying to get a full system overhaul for a 3000 sq ft 1970's cathedral ceiling home with oodles of windows and not very much roof insulation. We have hydro-air for the half the house with a basement, about 50 feet of baseboards in the quarter of the house that has a sealed crawlspace, and the newest addition (mid 90's) has radiant in the slab.

The only part of the house that has sufficient radiation to actually stay properly heated is the part with baseboards.
The hydro-air was self-installed by the previous owner, and has more bends and twists and curlicues than I have fingers, and I'd be surprised if half of the energy dumped into the fan moves even half of the heat into the conditioned space.

I've had 3 different companies come out to give estimates. The heat loss numbers they've come up with are *vastly* different from each other, and they all seem to be just throwing overkill at the problem.
One came up with a high estimate including rerouting all of the ducting and adding another hydro-air unit. They told me that in tall cathedral ceiling spaces, baseboards are not very effective.
Another estimate that was 3/4 the price that removed all the air systems and added baseboards to the area currently heated by air. They told me the opposite of the first, that baseboards are better for cathedral spaces.

The third gave a verbal description that they would go with baseboards, but then never sent the final estimate.

Is there a sheet that some of y'all use that I could do my own calculation so I could compare to one of these, or to another company, to get an idea if they are totally off base?


  • Jamie Hall
    Jamie Hall Member Posts: 23,668
    Well, first these first -- please edit your post to remove the prices. We never post prices for work; that's one of the rules.

    Now -- as to heat loss calculations. It is perfectly possible to do your own. Slant/Fin has a very good calculator for that purpose https://www.slantfin.com/slantfin-heat-loss-calculator/ which isn't hard to use and is plenty accurate. Not a bad idea to roll your own just to check.

    Heating a space with a cathedral ceiling can be done perfectly well with any type of heat. What does need to happen, though, is you need ceiling fans to get the heat down to where you are.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Erin Holohan Haskell
  • vilord
    vilord Member Posts: 48
    Prices removed, thanks for the reminder!
    The lady of the house really hates ceiling fans... perhaps we will need to discuss some modern-look fans that fit her aesthetic, but are there any options that move the air without ceiling fans?

    Years ago I watched a this-old-house about high speed forced air, but I imagine installing ducting up through the walls so it blows down will be cost prohibitive...

    I'll give the slant/fin calc a try. Thanks!
  • pecmsg
    pecmsg Member Posts: 4,967
    She can be comfortable, learn to like ceiling fans or major renovation!
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    I (not a heating professional) did a heat loss three different ways for my house when converting from a 1950 GE oil-fired boiler to a May 2009 natural gas fired mod-con.

    Method 1: My old boiler always supplied enough heat and it had a 1/2 gallon per hour nozzle, so somewhere around 75,000 BTU/hour was surely enough.

    Method 2: A (formerly good) heating contractor said my house was like a lot of others and they always installed 100,000 or 120,000 BTU/hour "just to be sure." He paced the width and depth of my house (estimating downstairs floor area, I suppose).

    I then read John Siegenthaler's big book and decided Method 1 was better than method 2, but not enough. I forget if I got that big worksheet method, or found the Slant/Fin calculator. I know Siegenthaler's book came with a CD that had a program good enough for residential work. He also sold a complete program for money, but I did not need that. I then calculated I needed something like 50 or 60 thousand BTU/hour at design temperature if both zones were calling for heat and the indirect wanted to recover. I also read W-M's installation and operating manual. So call this Method 3.

    The heating contractor sold only Weil-McLain mod-cons (and lots of non-mod-cons), and recommended the 105 thousand BTU/hour one. I insisted on the smallest one available at the time (80 thousand BTU/hour). Design temperature around here is 14F.

    Problems with my method is that it was not accurate enough, so when I calculated the required resets, they were not good enough, and I diddled them for a couple of years to get them really right. It is tough to figure out the heat losses of a house when you do not know the details of construction (insides of walls). Also, even though I got the smallest mod-con I could from the contractor, it is too big, so I had to set the resets for upstairs (baseboard) to higher temperatures than I would like to prevent rapid cycling; the heat loss there is not high enough to consume what is available even when the boiler is modulated all the way down to 20%. But although design temperature is 14F around here, it went down to 4F two days ago, and to 9F last night, and the system had no trouble keeping up.