Does clogged radiators increase the heating bills in a tankless combi boiler setup?

Question

We moved to a "new" apartment and I was told by a family member that all the radiators are clogged like hell and we should get them cleaned ASAP which we never did.

What makes me paranoid is that, if uncleaned radiators and pipes mean higher heating bill or less heating bill. When I think about it, minerals in unfiltered hard water isn't really good for transferring heat and that should mean less heating bills. It also means the pipes are clogged and thus less water circulating the radiators also meaning less heating bill. I tried making the gas heater to work at 90 and there was only a minor difference in heat of the radiators. The interior of the house was so cold I once woke up at night and my nose was dripping so bad I couldn't sleep under two layers of blankets.

The natural gas combi heater seems to be a really old design. Ferroli Domiproject F24.It starts to give gray water if I open the hot water tap over the faucet too much. I honestly don't know much about plumbing but I guess it tries to give me dusty water from the radiator loop?

In the end I am unsure if never cleaned natural gas/hot water radiator systems burn less gas when uncleaned especially old devices.

Answer 1

I think you're looking at it a bit wrong. It doesn't matter if it burns more or less gas, or stays hotter longer or circulates less. That's not how you reduce your heating costs.

You want it to transfer heat as efficiently as possible from the burner to the room you're trying to heat. That means heating the water, having the water hold onto as much heat as it can getting to the room, and releasing as much heat as possible into the room.

A clogged up radiator that has minerals clinging to the tubes and insulating the water prevents heat transfer. And bad clogs reduce the amount of water that can be pumped through it, further reducing the heat you're getting.

That causes the system to call for heat continuously, keep trying to heat the room and not make much progress. It'll keep calling for heat until either the system gets too hot and shuts down, or the thermostat in the room eventually reads the temperature you set. Even if an uncleaned, poorly working system burns less gas per minute, it'll run far longer more than canceling out those savings.

If you want to reduce heating costs, turn the temperature on the thermostat down. But you still want the system working as efficiently as possible. An inefficient system is just putting all the heat into where the boiler is instead of the room where you want it.

Answer 2

I'm not sure I'd be "paranoid" about the situation, but a little bit of logical thinking would lead one to believe that a clogged system won't heat as well as a clean one and that would, therefore, lead to higher heating bills.

If the pipes are, in fact, clogged with mineral build up, then that means they have, effectively, a smaller inside diameter than when they were installed. Since pipe has a non-zero cost, and the larger the pipe, the higher the cost, it stands to reason that the piping and radiators were likely installed with about the smallest sizes that were reasonable to adequately heat the house - anything larger would have cost more for no added benefit.

Since the clogged pipes are now smaller than they were at installation, the flow through them is going to be lower. Since the low flow isn't getting as much hot water to each radiator, each radiator isn't putting out as much heat as it used to. Therefore, you have to flow hot water over a longer period of time to get the same amount of heat out of the radiator. Increased flow time means the pump(s) has to run longer, using more electricity, and that the boiler has to remain fired up burning more fuel (gas, oil, electricity, whatever) for longer to produce the hot water to pump.

Both of these situations will lead to higher heating costs in the long run.

Simply replacing an old boiler with a newer, more efficient one will get you a more efficient production of hot water, but if that hot water can't get to the radiators, you're simply producing and wasting that heat more efficiently.

Sounds like it's time to clean if possible, and replace if necessary, all those hot water pipes. It's likely that giving the boiler a good clean would also be quite useful. I'm not familiar with domestic hot water heating, so that may not be a reasonable option and going straight to replacement may be the way to go.

Of course, these are capital expenditures, and since you're renting (the US use of the word "apartment" indicates that), this will be on the landlord. The landlord may not be highly motivated to spend the money to do so, since you're paying the heating bill and he would pay for the cleaning/replacing. At a minimum, expect your rent to go up once he gets this taken care of.

Answer 3

Take the word from manufacture:

"Combi boilers are designed to accomplish both space and water heating with a single appliance. Like a tankless water heater, a combi boiler provides hot water on demand. It can also seamlessly switch between water heating and space heating to provide the best possible experience."

While the single appliance (water heater/boiler) supplies the hat water, the piping is responsible for delivering the hot water to the faucets, and to the radiators to emit heat to warm up the surrounding spaces. Unlike the faucets, the piping and radiators form a loop to allow constant hot water circulation to meet the heating demand (temperature setting), so an inefficient piping system and clogged radiator will restrict the flow of water, thus the spaces will need longer time to heat up. Note, the total water for heating is the same for both (efficient and inefficient) cases, but you will feel less comfortable when the space warms up too slowly, and the latter case will need more gas to heat the water, which tends to cool off much faster due to the reduced water stream, and longer exposure in cold spaces.

BTW, I think you shall bleed the air out of the radiators periodically, and upkeep the heating device if you are responsible for it.