UFH in the bathroom - wet system or electric?

[Great_scot_selfbuild]

Our design is for a very well-insulated timber frame house (walls & roof both U=0.11, triple glazed windows, 0.6ACH etc.). We’ve always been working on the principal that the UFH downstairs will provide enough heat for the house and upstairs we’ll just need towel rails and MVHR. I’ve read/been told that MVHR isn’t to be assumed as a system for redistributing heat around the house, but I’m just going by what we’ve seen on a passive haus locally and it certainly works.

 

When it comes to the bathroom we realised that we probably do want some UFH of some kind, but perhaps this could just be an electric system and used on requirement.

 

For those who have taken a similar approach, what are your experiences? I’m worried about the cost of an electric system as I’ve no idea on its efficiency/power consumption and as a result I’m wondering if we should just look at factoring in a wet UFH system for the bathrooms before we finalise the floor levels of the other rooms (don’t want a step between the bathroom and adjoining rooms).

 

One of the responses I’ve had back when going out for quotes for ASHP simply stated that “MCS requires rooms to be under 10watts per m² for no emitters to be allowed upstairs”. I’m going through the SAP heat loss calcs at the moment, has anyone encountered this being an issue if it’s slightly over 10w/m²? Does building control care?

 

Copy of the upstairs floor plans and section for context / interest - the ceilings are very high, so when it comes to heating and sizing the MVHR I’m trying to work out how much the volume affects the sized of ASHP and MVHR.

[WannabeBob]

We are doing exactly this, with wet UFH downstairs and only electric resistive (towel rail and bathroom) upstairs. It should be very quick to heat up so I don’t think will take too much power to run especially if it only comes on at specific times of the day and on a sensor when we detect presence. 

 

However… that’s still the theory and we are still building so I suppose I can’t say yet that all of that will work!

 

We are at <10W/m2 though so can’t comment about that yet

[JohnMo]

3 hours ago, Great_scot_selfbuild said:

MCS requires rooms to be under 10watts per m² for no emitters to be allowed upstairs

Never seen that requirement in any MCS documents!

 

But are you not just paying MCS (suppliers tax, more profit) to go that route. If you are insulated as we as you say, you should only be needing a circa 6kW heat pump?

 

3 hours ago, Great_scot_selfbuild said:

the ceilings are very high, so when it comes to heating and sizing the MVHR

High ceilings affect form factor, so you have a bigger surface area exposed to the outside. You just do the room by room heat loss calculation as normal, you will just have more wall and more roof exposed (if vaulted). Small impacts on a well insulated house.

 

Depends on where you are in the country for ventilation, just follow building regs guidance to size, England is different from Scotland. You will be turning the system down after completion anyway, because you end up over ventilating at BR rates.

 

Bathroom heating, you normally want bathrooms warmer than bedrooms, so you need heating in them. Bedrooms can be ok at 18-19, bathrooms will feel very cold at that. With a cooler bedroom they suck the heat from ensuites, so you need bigger than calculated towel rails.