Monoflow Radiators to Home run manifolds

Matigi

Hi there,

I purchased a 1800 sqft home with a Monoflow setup, and 12 year old cast iron boiler. While renovating we removed all walls from the main floor, and had to change the original paths to the upstairs radiators. In doing so we've encountered lots of issues with trapped air and poor flow to the upstairs radiators.

I'm planning on scrapping the Monoflow setup for a 12 run manifold, home run setup, having each radiator in the home directly piped to the manifold, and the manifold directly plumbed to the boiler with a single variable circ pump.

Heatloss calcs are 69K BTUs, and the boiler is rated at 80K. I was planning on going to a variable speed Alpha2 circ, and eventually installing some zone control actuators. I am concerned that without all the heat mass that the monoflow piping contained, that i'll run into issues with cycling. Does all of this sound OK? Is it a good time to upgrade the boiler to a modulating efficient model.

Do I need a primary/secondary circuit, or can I get away with just a primary circuit with the variable speed pump?
I'm envisioning a simplified system plumbed similar to this:




Apologies for some of my ignorance. We're out of money, and I'm trying to learn as much as I can to get my family into this house.

Appreciate any advice.
Matt

Pulse

Your real heat loss is probably somewhere around 30k BTUs for 1800 sqft, unless you have zero insulation. If you upgrade to a new condensing boiler, lets say ~80k BTUs, make sure it has a 10:1 turndown. That way you can go down to 8-8.5k BTUs and prevent short cycles.

Matigi

It is a double brick home with no insulation and 1 inch strapping behind plaster walls. the radiators are also mounted flush with the walls, and inside the 1st layer of brick...

mattmia2

You will need to ensure minimum flow is maintained through the boiler, probably with primary/secondary pumping or a bypass unless you can ensure the smallest zone will have the minimum flow, but the higher flow in the zones could give you more short cycling issues when only a zone or 2 is calling. Most mod con boilers also have configurable controls to reduce short cycling.

Jamie Hall

Heat loss with that construction may not be far off. You really should do primary/secondary...

Otherwise, carry on. You really aren't losing much thermal mass, so I wouldn't worry about that.

Matigi

Appreciate the advice. For now, all zones/runs will be open, and adjusted at the manifold for flow. Zoning may be more of a long term project.