New boiler questions

RavingMad

Looking to replace our Ideal HE 18 in the next month or two and our engineer has quoted £1.6k for a Baxi and £1.8k for a WB. Both 18kw regular boilers.  I was thinking of getting him to replace the radiator in our living room as it's never warm enough in winter. Would it be the ideal time to do this? Does replacing the boiler involve draining? I imagine that's the case as he's doing a cleanse and system filter?

Thanks 

Veteransaver

The system is generally drained and flushed with a new boiler yes.
Are you sure the radiator needs replacing and it isn't just a sticky or clogged valve? Unless it's undersized for the room, but if it doesn't get hot like others in the house then it is likely an issue with the valve. But a good idea to consider changing the valves whilst the system is drained. Then if the radiator does need replacing for whatever reason it can be done without draining down again.

FreeBear

The system will need draining down - Not normally a major task. So an ideal time to replace radiators.

I'd suggest running the numbers through a heat loss calculator for every room using a Delta T of 40°C or even 30°C. this will allow you to run at a lower flow temperature which gives greater efficiency and therefor lower running costs. Coupled with a programmable thermostat that allows you to set different temperatures during the day/week, you could potentially save 10-15% each year. In reality, more likely 5-8%, but still worth doing.

Having looked at some of the Baxi boilers, I'm not that impressed with the modulation range - The WB Greenstars will modulate down to around 3.3kW which means the boiler won't be short cycling too often (bad for fuel consumption & long term reliability if it does).

While you are getting quotes, do get a price from someone like Octopus for a heat pump - They gave me a quote earlier in the year that wasn't much more than i paid for a gas boiler.

RavingMad

The radiator gets hot enough but not the room.  Running the calculator with my rough estimates and it quotes 9k btu? Modern house, corner living room with patio doors and windows to either side. We have a stove fire in there, so it's fine in the evenings.

I have had an initial quote from Octopus, 2.6k. Pretty good price for a heat pump but not sure I want to be monitoring it all the while to ensure I'm getting the best out of it.  Plus reading about how people aren't getting the heat that they previously had would annoy the family 

Some time in the future I was toying with the idea of converting the garage so extra radiator.  Would 18kw cope with 14 radiators? I don't think our boiler gets stressed at winter, I don't think it goes above 10kwh but I need to double check that

Thanks 

FreeBear

9000BTU or ~2.6kW - That equates to a 600x1600mm Type 22 radiator, which is pretty darned big.

It might make more sense to fit two smaller radiators, say a pair of 600x1000 type 21 (4500BTU each) or 600x1200 type 21 (5470BTU each).

The £2600 quote is pretty darned good, and once tuned, you don't need to be monitoring it constantly. But if you did go the HP route, I'd suggest pushing for bigger radiators all round. Bigger radiators means lower flow temperatures which in turn gives higher efficiency & lower running costs (also applies to condensing gas boilers).

I suspect an 18kW boiler is well overrated for the number of radiators you currently have. So it should have plenty of spare capacity to run an extra radiator or two. Got 9 radiators here (total output around 10kW) coupled to a combi boiler rated at 24kW for heating. Most of the time, it is ticking over at 4-5kW and only hits 10kW for a minute or two at start up.

Albermarle

RavingMad said:

The radiator gets hot enough but not the room.  Running the calculator with my rough estimates and it quotes 9k btu? Modern house, corner living room with patio doors and windows to either side. We have a stove fire in there, so it's fine in the evenings.

I have had an initial quote from Octopus, 2.6k. Pretty good price for a heat pump but not sure I want to be monitoring it all the while to ensure I'm getting the best out of it.  Plus reading about how people aren't getting the heat that they previously had would annoy the family 

Some time in the future I was toying with the idea of converting the garage so extra radiator.  Would 18kw cope with 14 radiators? I don't think our boiler gets stressed at winter, I don't think it goes above 10kwh but I need to double check that

Thanks 

I have a 18KW WB and 13 radiators of various sizes and it copes well.

The issue with a heat pump is that it normally needs to be on for more hours to get the house warm, as it does not heat the central heating water to the same temperature. So you need to plan ahead more. For example it comes on at 03.00 rather than 06.00 on a cold morning. 

FreeBear

Albermarle said:

RavingMad said:

The radiator gets hot enough but not the room.  Running the calculator with my rough estimates and it quotes 9k btu? Modern house, corner living room with patio doors and windows to either side. We have a stove fire in there, so it's fine in the evenings.

I have had an initial quote from Octopus, 2.6k. Pretty good price for a heat pump but not sure I want to be monitoring it all the while to ensure I'm getting the best out of it.  Plus reading about how people aren't getting the heat that they previously had would annoy the family 

Some time in the future I was toying with the idea of converting the garage so extra radiator.  Would 18kw cope with 14 radiators? I don't think our boiler gets stressed at winter, I don't think it goes above 10kwh but I need to double check that

Thanks 

I have a 18KW WB and 13 radiators of various sizes and it copes well.

The issue with a heat pump is that it normally needs to be on for more hours to get the house warm, as it does not heat the central heating water to the same temperature. So you need to plan ahead more. For example it comes on at 03.00 rather than 06.00 on a cold morning. 

Many people will run a heat pump 24/7 leaving the thermostat to control the temperature and just dial back a couple of degrees at night. When the HP does kick in, it chugs along low and slow.

With a gas boiler, they are often set to fire up and heat the property up as fast as possible with high flow temperatures. For some users switching to heat pumps, they try and replicate this behavour. In both cases, it leads to poor efficiency, higher running costs, and impacts on long term reliability.

You have the choice of running hard & fast generating (for example) 10kWh in short bursts, or going low & slow using 5kWh for longer. The house will still lose heat at the same rate regardless of which strategy or fuel you use. I'm still burning gas and use the low & slow method. Boiler efficiency is up around 96% with a flow temperature of 40-50°C. I could run with a 70°C flow, but this reduces efficiency to about 86%. With a heat pump, the difference in efficiency when increasing the flow temperature is even worse - Potentially going from 400% down to 200% or even 100%.

Low & slow will use less energy over the course of a day compared to hard & fast.