How often do you get the heating curve right?

Alan (California Radiant) Forbes

It's your last day on the job where you've installed a new system or replaced the boiler with a condensing boiler that has outdoor reset controls and it's time to program the high and low water temperatures. You've done this hundreds of times before with all different kinds of heat emitters in all different kinds of houses; you're a professional. Are you confident enough to know that you will nail it or are you more cautious and brave enough to start with lower water temperatures with the goal of better efficiency? Or are you the kind of responsible contractor that doesn't want any call-backs and wants to keep the owners happy, choosing higher water temperatures than what you think is necessary; to hell with efficiency?

STEVEusaPA

How often?....Every time...eventually...lol
It would be nice if we had the ability to fully monitor the system remotely and tweak as the season unfolds.
I did a full, over the top, detailed heat loss on my own install. I had all the temps, loop lengths, flow rates, etc. Still ended up too big, and curve too high.
I farted around with settings, curves and manifold flow rates for probably 2 full winters and I still can't get 24/7 operation on or below design day (oil system).

I think it's best to start with what your math told you. Maybe tell the customer you biggest concern is their comfort and maximum system efficiency, so you'd like them to make a simple journal and you'll come back to see if any adjustments are warranted. Of course you have to be careful that you don't end up married to their system.
Depending on weather, I usually set it based on my math, and check with my gauges and my Flir. Stop back a short time later when it's very cold (hopefully on design day) and see how it's performing, recovering (and to check my work and look for any leaks/potential issues).

Alan (California Radiant) Forbes

I have the same experience. It tells me that my math is nowhere near the empirical data although my heatloss calc's. certainly get me in the ballpark and highlight areas that might have problems.

And from the customer's point of view, it is very disconcerting to have spent a large pile of cash on a system that is not keeping them warm. No matter how often you tell them and prepare them for a little bit of experimentation, many will get upset that they're not warm.

Leon82

I was on another forum and one of the guys used the fuel use to calculate the water temp on design day. It was fairly close.

For the low I found with my fin tube anything under 115 to 120 was not stable enough for comfort

Big Ed_4

I would go with the recommended , What would that be 167* at 13* , I think ? Then maybe tweak after they close their AC defusers and block up the return on the coldest day of the year.

Turbo Dave

I use Tekmar controls with communicating thermostats that provide indoor feedback, in addition to outdoor reset. This allows the lowest possible supply temperature to heat the coldest zone. Even baseboard heat convectors will operate with condensing supply temperatures most of the season. You are also guaranteed to provide a high enough supply temp to heat the house on the coldest day of the year, -55 in my location. All guesswork eliminated, the most fuel savings, and a warm customer. I can't recommend this enough.

motoguy128

I err a little on the high side and lean on the “boost” function to handle the rest.  

my boss used to never install the outdoor sensor as it could result in a call back.  Nobody calls back if they get 2% less efficiency because honestly they have no idea.  

But the last 2 Combi installs I used it.  I figure it reduces short cycling and overheating spaces in mild weather.  

STEVEusaPA

Leon82 said:

I was on another forum and one of the guys used the fuel use to calculate the water temp on design day. It was fairly close.

For the low I found with my fin tube anything under 115 to 120 was not stable enough for comfort

We do it on this forum too, Fuel use to btu sizing of equipment.
https://forum.heatinghelp.com/discussion/181448/trying-to-identify-best-sizing-and-models-for-a-new-boiler#latest

Skyline

By no means I am a professional, at least not in this area...

Based on my very limited experience, about three month with my new condensing boiler, I have to agree with @STEVEusaPA :

How often?....Every time...eventually...lol

It is actually sad, that for even the professionals in this area will take about two winters to set the heating curve correctly.

Provided that they'll take some time and effort to help out the homeowner to recover some of the cost of the condensing boiler. Instead of just leaving the heating curve at its default and advising the homeowner to run it like this at least for a year. Like my contractor did...

Instead, I did that some of you have done, do the calculations and set the heating curve to a value, that provides a warm and comfortable house...

tim smith

I'm with erring on the side of efficiency and using boost feature after say 60 mins. Use a indoor stat with intelligent recovery. The intelligent recovery will start it earlier to help compensate for the slow warm up time. The boost finishes it off if not coming up. Usually when we are doing old 1920s bldgs, some updated windows some not, we can set design water temps around 150 at 24 od (seattle design) and a minimum of say 90 or so. We are definitely not batting 1000 but maybe 500?

ratio

Batting .500 would get you millions. Good job!

flat_twin

Design for my area is 5 degrees and I initially set the low end of the ODR at -5 which was fine for the first heating season. The following winter we had a "polar vortex" that sent our temps down to -20 for a few days and the boiler did not keep up with heat loss so I made adjustments to cover those rare temp swings. 88 SWT @ 55 outdoors to 138 SWT @ -20 gives long heating cycles and covers windy days too.
I think your best calculations will get you so far with setting up ODR but a couple heating seasons are needed to fine tune it.

Suzook

Took me 3 years