Drop header benefit other than height?

ChrisJ

Gary Smith said:

I agree with @JamieHall's comments. Also remember, the radiators were sized, approximately, based on the location's design winter temperature and the structure's heat loss. The whole sizing of both radiators and boilers is at best an educated guess guided by experience. I suspect too the pickup factor was arrived at, not by some exact engineering calculation, but by experience of suppliers/installers who hit on the 25% factor as a compromise point at which they didn't get too many complaints of too small or too large boilers. Because of all the factors involved, I don't think it pays, in either dollars or time, to get too precise, because on all days when the outside temperature is higher than the design day (most of the time) the boiler is oversized, on the few days the outdoor temp is colder, the boiler is undersized, so most of the heating season the system will operate outside it's perfectly and precisely selected design point.

The 33% which is the standard was calculated I believe sometime in the 1940s.
@gerry gill had shared an article on it a few years back.

I highly doubt an actual heat loss was done on my house in the mid 1920s. I'm sure thought was put into the sizing, but I don't think anything near what we expect today.

However, one was done on it in the 2010's by me just as all of us can do them and compare the installed radiation to the loss. We can then make a decision on what size boiler to install based on that information as well as piping losses.

In my case I have 94,000 btu/h worth of radiation in a house that needs around 65,000 btu/h. 72,000 at most. I used a 150K input 125K output boiler for a few years and then dropped to 125K input 104K output and it was much better. A lot quieter... easier on vents, easier to control temperature and overshoot.

This is why I push for others to use a 10-20% number rather than 33% for residential applications.

AdmiralYoda

I have a couple rooms that have radiators that were waaaaaaay to large. They put big ones in there because once upon a time it was a room addition with no insulation on the walls and barely anything in the ceiling. It got cold fast and then when the heat came on it got too hot fast!

After insulating it properly it is barely bearable when the heat is on, even with a TRV and a small vent. I've been thinking of removing sections of the radiator to match the calculated heat loss.

This will save me enough EDR that I can go to the next lower sized boiler with about a 15-20% pickup factor. Probably a good idea. Even though it is a tiny boiler and only requires one 2" riser (Peerless 63-03L) I still plan to put two risers with a drop header on it. Just because I can. It might not make it work any better but it will make me feel better about it.

ChrisJ

AdmiralYoda said:

I have a couple rooms that have radiators that were waaaaaaay to large. They put big ones in there because once upon a time it was a room addition with no insulation on the walls and barely anything in the ceiling. It got cold fast and then when the heat came on it got too hot fast!

After insulating it properly it is barely bearable when the heat is on, even with a TRV and a small vent. I've been thinking of removing sections of the radiator to match the calculated heat loss.

This will save me enough EDR that I can go to the next lower sized boiler with about a 15-20% pickup factor. Probably a good idea. Even though it is a tiny boiler and only requires one 2" riser (Peerless 63-03L) I still plan to put two risers with a drop header on it. Just because I can. It might not make it work any better but it will make me feel better about it.

If you can get the system to run more, shorter cycles it'll greatly help those TRV's do their jobs with the oversized radiators.

Are you using a Honeywell thermostat, and if so do you know what CPH you're using?
I'd try 2 or 3 CPH and give it a few days to settle down after changing the setting.