MHRV and back boiler questions

soldsold

I'm finally getting my head around heating systems basics. I would value any of your "True or false" answers to the following assumptions/ observations/ statements:


1) A backboiler takes out a lot of the heat from the room where the stove is, preventing the room from overheating if the room is superinsulated.

2) A backboiler has some issues when power cuts out - where to dump the hot water from the bolier?.

3) Powercuts are less of an issue with vented systems.

4) An MHRV system does not spread heat around the house fast enough to prevent the room where a stove is from overheating (if the stove is oversized for the room).

5) An MHRV cannot have different temperature settings in different rooms/ zones, although you can balance the flow of air to have some crude control.

6) You should not have showers/ cooker steam entering the MHRV heat exchanger pipework as bugs can grow in there more easily.

7) Once general maintenance is done, and filters are changed, MHRV systems should be safe to use.

8) The ideal humidity levels are between 40 degrees and 60 degrees. MHRV systems dry out clothes quickly but the air can get too dry (not sure of this one!)

9) Solar panels provide hot water during the summer but still have a long payback time.

10) Solar panels can provide low temp hot water for space heating in winter but the lack of solar energy and inefficiencies at low external temperatures mean there is very limited heating actually done.

13) In my project the current bungalow has radiators and an old boiler and an old uninsulated water tank. The new 250m2 extension will have MHRV, a solid fuel stove with backboiler, and backup radiators piped in just in case they are needed. I should install pipework for a future solar hot water system as the roof faces due south

14) I should now also install a bigger (eg 300 litre) hot water tank with a coil for hot water.

15) To get all of these heating systems working together I need a very competent and experienced system designer, not the local plumber.(Suggestions by PM of really good and experienced heating engineers/ designers would be very welcome!).

13b!) I will find it impossible to use radiators/ MHRV's/ stove/ backboiler and have individual room temperature control, programmable for different times of the day.

Thanks!

Steve

CJhaughey

1.f
2.t, But you should fit a Rad anyway and also try and use convective pipework if possible.
3.?
4.T
5.T
6.F
7.T
8.F
9. Hard to answer depends on a lot of things.
10.T
11.
12
13 Yes make arrangements for future solar DHW, cost is little for pipework
14. Yes or bigger if you have a family or are planning one.
15 yes
13T

soldsold

Thanks for the reply.

My understanding was:

A stove (eg 6kw) with a back boiler puts out less heat into the room where it is positioned than a (eg 6kw) stove with no back boiler as a lot of the heat (eg 60%) goes to the radiators, allowing you to run the stove without turning the room into a furnace.(No. 1)

Is the use of a radiator with copper pipework sufficient to prevent overheating in the event of a power cut? (No. 3)

Its good to hear that you can recover heat from shower rooms and cooking area, I had just read that some recommend not to as mould/ mildew are coaxed to grow in the mild humid climate in the pipework (No. 6)

Is there a way to regulate humidity? I know cellulose/ hemp/ quinnlite blocks all help but if not using these? (No. 8)

You are right to ignore 11 and 12 the questions were a bit juvenile...

Carlow52

With a SFS c/w BB: the issue for me is that if you want the rads heated u also have to heat the room that the SFS is located.
The reverse is also true so if u just want a quick fire for an hour or so in the room and u need, from your example 2 kW, then another 4 kWs must be used else where: no choice.

Re HW tanks if considering solar u need 2 coils with the solar one at the bottom. 3 coils if including SFS

A bigger tank now, like the poor, will always be with you so perhaps consider a combi boiler as opposed to a big tank now and u can vary the amount of HW required.

If considering solar with a combi then put the tank is now and u can use the solar to preheat the water for the combi: the input temp is limited but can be done.

Re 13b!) if u want <<individual room temperature control, programmable for different times of the day.>> forget about the BB and individual room control is a doddle

En passant, if u were not going to use the MHRV in the 'moist' areas then what heat were u going to recover?

Am not being smart here, just want to make sure you have the right process in mind.

ps: for BB go inch copper from the boiler and go straight up with expansion pipe to the header tank, which should be covered

soldsold

Carlow52 wrote: »

With a SFS c/w BB: the issue for me is that if you want the rads heated u also have to heat the room that the SFS is located.
The reverse is also true so if u just want a quick fire for an hour or so in the room and u need, from your example 2 kW, then another 4 kWs must be used else where: no choice.

To avoid heating other rooms unnecessarily what about putting a radiator in the same room as the stove and a programmable control system that would just run that one radiator until the room heated up (or another one or two if one could not take all the heat)?

When needing to heat other radiators in other rooms - and to avoid heating the room where the stove is - I could just use the current oil boiler?

Carlow52 wrote: »

Re HW tanks if considering solar u need 2 coils with the solar one at the bottom. 3 coils if including SFS

Good advice, thanks.

Carlow52 wrote: »

A bigger tank now, like the poor, will always be with you so perhaps consider a combi boiler as opposed to a big tank now and u can vary the amount of HW required.

If considering solar with a combi then put the tank is now and u can use the solar to preheat the water for the combi: the input temp is limited but can be done.

Is there a good reason most people selfbuilding dont use combi boilers? Are they a realistic option for houses with families, pumped showers, etc? Anyone I have known that have been building have not considered them, and I had the impression there were must be good reasons why - eg limited volumes of hot water?.

Also is there much of a loss in heating-hot-water efficiency to have a big hot water tank if only using the top coil most of the time?

Carlow52 wrote: »

Re 13b!) if u want <<individual room temperature control, programmable for different times of the day.>> forget about the BB and individual room control is a doddle

Can you explain this point further if you dont mind, I would have thought that TRV's on radiators would be able to throttle back the flow of hot water even if the heat was coming from a back boiler? Of course if the BB is producing too much heat it has to go somewhere, and in most cases if the stove and BB are on I cant imagine being upset if the hall/ spare bedrooms got a bit too warm. Is there another reason individual room controls and BB's cant work together?

I cant imagine I'll be able to use a stove without BB as the living room will be very well insulated and will overheat very quickly unless some of the heat is taken away through the BB/ rad's.

Carlow52 wrote: »

En passant, if u were not going to use the MHRV in the 'moist' areas then what heat were u going to recover?
Am not being smart here, just want to make sure you have the right process in mind.

I understood that while a burst of heat comes from showers/ cookers for a short time during the day, the main heat recovery was from the rest of the house - basically heat from the radiators/ stove in the room was recovered as the air was being extracted and refreshed? Of course, I would prefer to recover all heat, had just read some (a lot) of reports about MHRV health risks from mildew etc growing in the ductwork and filters and had read it would be best to sarcrafice the wetroom heat for this reason.

Carlow52 wrote: »

ps: for BB go inch copper from the boiler and go straight up with expansion pipe to the header tank, which should be covered

Thanks for the advice, I've noted it for when the job comes up.

Cheers,

Steve

Carlow52

soldsold wrote:

To avoid heating other rooms unnecessarily what about putting a radiator in the same room as the stove and a programmable control system that would just run that one radiator until the room heated up (or another one or two if one could not take all the heat)?

When needing to heat other radiators in other rooms - and to avoid heating the room where the stove is - I could just use the current oil boiler?

The critical issue here in my view is that the boiler has its own limit stat on it so if rads are shut down, the circulating water reaches the limit stat temp sooner and the boiler kicks out. The SFS just keeps increasing the water temp. IMO, based on 30 plus years of back boilers is that they work best with no TRV's or other controls. I would say that TRV's on BB boiler rads are dangerous
I would just put in a nice stove and spend the money on controls for the oil. While I am told it can be done I will never put a SFS with BB on a closed rad system.

soldsold wrote:

Is there a good reason most people selfbuilding dont use combi boilers? Are they a realistic option for houses with families, pumped showers, etc? Anyone I have known that have been building have not considered them, and I had the impression there were must be good reasons why - eg limited volumes of hot water?.

I think cost was the issue due to small production runs coupled with a reluctance by joe basic plumber to think beyond the basic meat and 2 veg boiler:) Just look at the slow take up with condensing and the issues with maintenance. I have not fixed on a final set up yet but the idea of feeding a combi boiler with solar preheated water must help with the volume of hot water issue. In addition while there may be multiple pressurized showers in a house, the need to have them all going at the same time should never in my mind be the design requirement. One at at time SJ:)

soldsold wrote:

Also is there much of a loss in heating-hot-water efficiency to have a big hot water tank if only using the top coil most of the time?

The top coil will still heat more than half the tank in most cases

soldsold wrote:

Can you explain this point further if you dont mind

see above

soldsold wrote:

I would have thought that TRV's on radiators would be able to throttle back the flow of hot water even if the heat was coming from a back boiler? Of course if the BB is producing too much heat it has to go somewhere, and in most cases if the stove and BB are on I cant imagine being upset if the hall/ spare bedrooms got a bit too warm. Is there another reason individual room controls and BB's cant work together?

I cant imagine I'll be able to use a stove without BB as the living room will be very well insulated and will overheat very quickly unless some of the heat is taken away through the BB/ rad's.

spec the stove for the well insulated room. Also remember u don't need to stoke it to the gills with very high calorific fuels. In addition, depending on the stove u can reduce the size of the firebox with firebricks to reduce the fire's output

soldsold wrote:

En passant, if u were not going to use the MHRV in the 'moist' areas then what heat were u going to recover?
Am not being smart here, just want to make sure you have the right process in mind.
I understood that while a burst of heat comes from showers/ cookers for a short time during the day, the main heat recovery was from the rest of the house - basically heat from the radiators/ stove in the room was recovered as the air was being extracted and refreshed? Of course, I would prefer to recover all heat, had just read some (a lot) of reports about MHRV health risks from mildew etc growing in the ductwork and filters and had read it would be best to sarcrafice the wetroom heat for this reason.

Not my area to be honest, I just posed the ? to see what you were thinking:(

soldsold wrote:

Thanks for the advice, I've noted it for when the job comes up.

based on the above maybe u will drop the BB:D

Cheers,

Steve

muffler

Carlow52 please read the forum charter in relation to posting text within a quoted post. That post above is a complete mess and clearly illustrates why we have this matter covered in the charter.

Cheers.

Carlow52

I agree it is a mess/tried to delete it but couldn't so please do the needful

muffler

Rather than delete it I tidied up part of it and will do the remainder after lunch